World Journal of Nano Science and Engineering, 2012, 2, 58-87 Published Online June 2012 (
Interface Recombination & Emission Applied to Explain
Photosynthetic Mechanisms for (e–, h+)
Charges’ Separation
Marco Sacilotti1,2, Denis Chaumont2, Claudia Brainer Mota1, Thiago Vasconcelos3,
Frederico Dias Nunes3, Marcelo Francisco Pompelli4, Sergio Luiz Morelhao5, Anderson S. L. Gomes1
1Department of Physics, Federal University of Pernambuco, Recife, Brazil
2Nanoform Group ICB & UFR Science and Technology, University of Burgundy, Dijon, France
3Departament of Eletronics and Systems, Federal University of Pernambuco, Recife, Brazil
4Plant Physiology Laboratory, Department of Botany, Federal University of Pernambuco, Recife, Brazil
5Institute of Physics, University of Sao Paulo, Sao Paulo, Brazil
Received January 31, 2012; revised March 3, 2012; accepted March 17, 2012
To copy natural photosynthesis process we need to understand and explain the physics underneath its first step mecha-
nism, which is “how to separate electrical charges under attraction”. But this Nature’s nanotechnological creation is not
yet available to the scientific community. We present a new interpretation for the artificial and natural photosynthetic
mechanism, concerning the electrical charges separation and the spent energy to promote the process. Interface (e–, h+)
recombination and emission is applied to explain the photosynthetic mechanisms. This interpretation is based on energy
bands relative position, the staggered one, which under illumination promotes (e–, h+) charges separation through the
action of an interface electric field and energy consumption at the interface of both A/B generic materials. Energy band
bending is responsible by the interface electric field (and the driving force) for the charges separation. This electric field
can be as high or above that for p-n semiconductor junctions (104 - 105 V/cm). This physical effect is not considered by
most of the researches. Without an electric field and without spending energy to separate electrical charges, any other
existing model violates physical laws. The staggered energy band type is the only energetic configuration that permits
charges separation under illumination and energy loss to perform the process. Application to natural photosynthesis and
artificial photovoltaic material and their energetic configurations are discussed. Examples for A/B being III-V/III-V,
TiO2/materials and II-VI/II-VI staggered energy band gap pairs are presented. In the proposed quantum mechanism,
plants are able to eliminate most of the 79% of the absorbed visible light, according to the published reflection and
transmission data. Moreover, the proposed mechanism can be applied to explain green fluorescent protein—GFP,
charge transfer states—CTS and Fluorescent Resonance Energy Transfer—FRET. As recent literature experimental
results propose photosynthesis as a quantum controlled mechanism, our proposition goes forward this direction.
Keywords: Solar Energy; Renewable Energy; Photovoltaic; Photosynthesis; Type II Interfaces; Staggered Interface;
Interface Emission; Interface Recombination; Quantum Photosynthesis; Solar Cell; FRET; GFP
1. Introduction
Synthesis using light is the literal meaning of photosyn-
thesis. It is the process by which plants are able to collect
electromagnetic energy, mostly solar energy, that is used
by organisms to synthesize complex carbon compounds.
More specifically, light energy drives the synthesis of
carbohydrates, which are essential for life. Thus, life on
Earth ultimately depends on energy derived from the sun.
Moreover, renewable energy is one of the most important
scientific and technological topics on the current days,
and a large fraction of the planet’s energy resources results
from photosynthetic activities in either present or ancient
times (fossil fuels).
Photosynthesis first step, which is light absorption and
separation of charges undergoing attractive electrical
forces, is the most important physical/biological mecha-
nism and should be copied in artificial systems such as
solar cells. Therefore, photosynthesis must be understood
at level of first principles, and based on physical para-
meters since photosynthesis is nothing more than a com-
plex physical process [1-3].
Life started on Earth 2 - 4 billions of years ago, when
the first two or more molecules got together, probably in a
puddle of water, absorbing light from the sun and sepa-
opyright © 2012 SciRes. WJNSE
rating both charges (e–, h+), perhaps catalysed by other
factor as discharge and/or with the mineral environment
participation. Since its first occurrence, this mechanism
and the evolution of species on Earth gave us only one
catalytic mechanism to separate oxygen from water [1].
The oxygen separation is one of the subsequent steps
after the charges separation on photosynthesis’ processes.
In the early days of Earth’s exuberant vegetation, most
of the available atmosphere gases were CO2 and N2. O2
had appeared with the evolution of the charges separation
process. Nowadays we have increased the CO2 level
from 200 (~1850) to 370 ppm (~2010) [1-3]. It has been
an important point for scientists looking for renewable
energy sources, and one of the issues is to copy the natural
photosynthesis approach, related to the (e–, h+) electrical
charges separation mechanism. The absorption of light
by organic molecules or inorganic nanomaterials doesn’t
provide the electrical charges separation directly. This is
just the first part of the process. If the material absorbs
light, the following step is its recombination within the
same material, releasing energy related the material’s
band gap energy (the forbidden band). To have (e–, h+)
charges separation requires a suitable energetic configu-
ration of the band gaps to allow the generation of the
necessary electric field to separate the (e–, h+) pair. This
electric field should arise from a potential variation. The
mechanism that separates electrical charges of different
polarities will be interpreted and described here. The
expression “separation of charges of different polarities”
means the separation of negatives, e–, from positives, h+,
electrical charges, which undergo an electrical attraction
called excitonic attraction. An appropriate electric field is
necessary to break the excitonic attraction, i.e. to split
both (e–, h+) charges, and hence energy must be spent.
Any model that do not account for the electric field and
the spent energy are violating physical laws. Our pro-
posed model accounts for both: the necessary electric
field and the spent energy. Furthermore, it seems to be
the only energetic configuration capable of providing
charges separation under excitation of light, and it is
based on staggered energy band gaps between two dif-
ferent materials of nanometric dimensions.
At the interface, A/B, between generic materials A and
B, there are naturally three possible energetic configura-
tions of the band gaps: type I, type II and type III [4-12].
Type I interface are largely applied to construct solid
state LEDs, laser, and most of the optoelectronics devices
[10]. Type I energetic interface can be represented when-
ever the energy band gap of one material is inserted
within the band gap of the adjacent material. Type III
energetic interface occurs when the band gaps do not over-
lap [4-8,10]. Only the type II interface, the staggered one,
shown in Figure 1 will be discussed here, concerning its
excitation by light and the bending of its valence and
Figure 1. Flat band configuration for A and B materials
staggered generic interface, representing the conduction
band (CB or LUMO) and valence band (VB or HOMO).
Note electrical charges (e–, h+) have always energetic steps
(electric potential barriers up or down) when travelling
from A to B or from B to A. This energy flat band configu-
ration is a non-excited system; otherwise it should be band
conduction energy bands. The band bending effect is caused
by charges falling down to lower levels of energy states,
creating a dynamic electric field that allows both (e–, h+)
charges separation [4,10,12].
This paper is organized as follows. An introduction to
type II interface and examples of applications on AlInAs/
InP semiconductor system and other systems such as
TiO2/II-VI and II-VI/II-VI, emphasizing their very effi-
cient mechanism for photon emission due to recombine-
tion of e– and h+ charges seated on different materials.
Intriguing results on reflection and transmission, avail-
able on specialized literature for plants, will be discussed,
for the first time, under the scope of physical principles.
These discussions concern transmission and reflection
experiments that give about 79% of absorption for natural
leaves at the visible spectral region. Such very high pho-
ton absorption should “fries” leaves in few minutes in the
absence of a fast optical emission mechanism to throw
away much of the absorbed energy. We propose here that
natural photosynthesis and artificial photovoltaics (nano-
metric systems) should be regarded as a quantum-con-
trolled mechanism, differently of the currently accepted
model, based on classical physics [1-10,13]. The present
proposal provides both: the necessary electric field and
the spent energy to separate negative from positive
charges. It will be applied and discussed for both inor-
ganic and organic systems. As explained below, the ener-
getic relative position between two different materials is
not a controversial question because modern organics
LEDs and organic solar cells devices uses this concept.
Moreover, many experimental results on energetic rela-
tive position and energy band bending on organics do exist,
excluding the frequent “controversial” argument to avoid
new ideas and explanation of the physical phenomena.
Copyright © 2012 SciRes. WJNSE
2. Current Representation of Energy Band
Offsets between Natural Organic Materials
Photosynthetic’ natural light reactions are represented by
energy bands of different molecules that absorb light and
transfer its energy to others molecules. This energetic
representation is called “ground state energy” (GSE)
[13-15]. According to Bjorn et al., the energetic relative
position for molecules on leaves is unknown [15]. If it is
unknown, experimental data should be performed to
know their offset to get to actual scientific systems. The
distribution of charges on excited organic molecules is
somewhat different from the distribution represented on
the GSE model. Unfortunately the GSE model, or repre-
sentation, does not apply to any actual physical configu-
ration; it leaves no room for feasible charge separation
mechanisms in natural photosynthetic process. Existing
electrical charges travelling from one to another different
material have always energetic steps (up or down). The
GSE energetic representation can not promote charges
separation since there is no driving force to break the
excitonic attraction [4,7,12]. Without the driving force,
the GSE model and energy transfer mechanism model
fails (see the discussion below, about fluorescence reso-
nance energy transfer—FRET and green fluorescent pro-
tein—GFP). According to current believes, leaves are
green to human eye due to chlorophyll molecules that
absorb light mainly in the red and blue ranges of the
visible spectrum; hence only light enriched in green
wavelengths (about 535 - 550 nm) is reflected from
leaves to our eyes [2]. However, there is no direct proof
that the green colour of leaves is mostly due to reflection.
In addition, there is no physical reason to explain why
the leaves’ colours are not related to emission. Note that
leaves are de-pigmented (i.e., absence of green colour)
when light is turned off. Equally, as presented below,
excitation of leaves with green or higher energy photons
gives many other colours’ emissions. As it will be com-
mented bellow, organic solar cells and organic LEDs,
composed of nanometer thin layers, uses the concept and
experimental results of staggered energy band gap con-
figuration, in contrast to the GSE configuration. As GSE
is not feasible in physical systems, the staggered band en-
ergy configuration (Figure 1) provides the major benefit
for the light reaction of photosynthesis: the electric field
(driving force) for (e–, h+) electrical charges separation.
At the interface, the electric field comes from the nearby
A/B materials interface energy band bending (Figure 2),
and the interface light emission can be related to the
spent energy, associated to the charges separation.
In conclusion for this section, organic molecules pre-
sent on leaves should experiment energetic (or potential)
steps for electrical charges movements between them.
Without these energetic steps it is impossible to propose
a mechanism for charges separation for the natural and
Figure 2. Type II interface representation under light exci-
tation of both A and B materials and the interface energy
band bending on both sides. These energy band bending are
created by the e– and h+ charges falling down to the lower
energetic steps at the interface (including possible tunnel-
ling of charges). The interface energy band bending creates
electric fields on both sides, responsible for the charge sepa-
ration to the opposite interface’s directions (the driving
force F & F+). h
i represents the interface photons energy
emission, related to the spent energy to separate (e–, h+)
charges under excitonic attraction. The interface energy
band bending (or the electric potential) gives rise to the
electric field EiA & EiB. Note that the h
i interface emission
is also issued from a tunnelling mechanism. Eext is the ex-
ternal electric field applied to the AlInAs/InP structure, as
explained in the text, to decrease the h
i emission intensity.
artificial photosynthetic processes. By using non-existing
physical energetic configuration (e.g., the GSE configu-
ration) we fail in explaining the physical mechanisms.
Any model based on non-existing energetic configuration
bring us to violate physical laws whenever trying to ex-
plain the physical mechanisms. The light absorption by
molecules within leaves is only the first step of the proc-
ess and it does not separate e– from h+. The next step, to
separate e– from h+, depends on the energetic configure-
tion between the existing molecules within the leaves.
Type II (staggered) energetic interface is proposed to
overcome the problem.
Copyright © 2012 SciRes. WJNSE
3. Current Energy Band Offsets
Representation between Inorganic
The artificial photosynthetic mechanism (applied to
modern solar cells) is currently and conveniently repre-
sented by type II interfaces (the staggered one, repre-
sented in Figure 1) [16-21]. But the model frequently
fails because the semiconductors interface band bending
phenomena is not considered, whenever charges fall
down to lower energy levels at the interface between two
A/B generic materials [4-7,10,16-21]. Only the flat band
configuration is considered for most of the artificial pho-
tosynthetic process. With no energy band bending con-
siderations, there is no electric field (driving force) to
separate both charges of different signals, as represented in
Figure 2. The staggered energetic representation for artifi-
cial photosynthesis does not consider that the falling down
of electrical charges at the interface is a sink for them
[16-29]. Once these charges cross the interface, they re-
combine there and they are lost because the recombine-
tion gives rise to interface emission [7,9,23-29]. This in-
terface recombination is erroneously and frequently called
charge transfer state (CTS) [27-29]. The authors do not
understand why the expression “charge transfer state” is
applied, since it is simply interface recombination and
emission. These CTS are applied to organic and inorganic
systems and it will be discussed below in more details.
Note that both natural and artificial photovoltaic mech-
anisms described above are dynamic systems, as repre-
sented in Figure 2. It is the near interface electric field;
created by the electrical charges falling down, that sepa-
rates e– from h+ [4-7]. This interface electric field arises
from a varying potential (or energy band bending).
Without illumination the flat band condition takes place,
as presented on Figure 1. As soon as (e–, h+) pairs are
no longer created (no excitation), there are no longer
electrical charges falling down to lower energy steps at
the interface. Without light, the equilibrium condition is
achieved and there is no more interface energy band
bending (no electric field, able to separate e– from h+, as
presented in Figure 2). At this moment, the interface
light emission stops. Note that the consumption of (e–,
h+) pairs at the interface (by interface emission) brings
the A/B system to equilibrium, without external excita-
tion. As the present proposal represents a different regard
on photosynthetic systems, it will be described below
step by step, bringing the necessary physical tools and
experimental proofs of its existence.
In conclusion for this section, inorganic photovoltaic
nanomaterials present the actual band offset (the stag-
gered one), but suffers from the mains physical tools to
separate electrons from holes: the necessary electric field
and the spent energy to separate electrical charges under
attraction. The physical laws’ violation is twofold in this
case, even though the experimental results are very im-
portant for solar energy developments. The physical me-
chanism to separate (e–, h+) is not present.
4. Physical Principle of the Charge
Separation Mechanism
According to the Nobel Prize Laureates L. Esaki (1973)
and H. Kroemer (2000), the staggered energetic configu-
ration between two different A/B materials, the flat band
configuration (no excitation), is presented in Figure 1.
This representation is only for the conduction band (CB
or LUMO) minima and valence band (VB or HOMO)
maxima at the momentum configuration (K space) [4-7,
10]. These minima and maxima are related to parabolic
energetic representation of energy on K space [10]. Under A
and B light excitation, it takes the configuration showed
in Figure 2 where we can observe: (e–, h+) pairs genera-
tion; e– and h+ jumping to lower energetic steps at the
interface and, consequently, the energy band bending of
both bands CB and VB in both A and B materials. Such
jumping of charges leaves both materials into a non-equi-
librium electronic state. Note that the jumping of charges
to the nearby material put both A and B materials under
non-equilibrium electronic condition [4,8,10]. This non-
equilibrium electronic condition should move both quasi-
Fermi energy levels on both sides of the interface. Mov-
ing both quasi-Fermi energy levels, should move (bend)
both CB and VB on both sides of the interface [4,7,10].
The interface energy band bending creates barriers for
few remaining electrons and holes (at the CB and VB of
both materials). These few remaining charges are no
longer allowed to go across the bended barriers. Their
thermal energy is not enough to promote tunneling across
these barriers. The electrical charges are therefore sent
away from the interface by the gradient of the electric
potential (the electric field being E = –grad V). They
represent the separated charges by the energy band bend-
ing action (and by the interface created electric field on
both sides of the interface) [4,10]. The (e–, h+) that fall
down to the lower interface energy steps recombine at
the interface, giving rise to the interface recombination
and photons emission (h
i). These emitted photons are
lost, representing a faster and easier way to efficiently
waste photon energy for A/B generic systems. Interface
energy band bending is frequently used as a result of
charges falling down to lower available energy levels [4,
7,10]. As the interface electric field (EiA, EiB, Figure 2)
comes from the potential variation at both sides of the
interface, we have the necessary electric field and the
driving force to separate electrons from holes. Note that
potential variation and energy band bending are related,
since energy = potential × electrical charge. Shortly,
most of the excited charges jump, creating the band bending,
and few excited charges do not achieve to cross the barriers
Copyright © 2012 SciRes. WJNSE
created by those crossing the interface. A support infor-
mation file represents the proposed mechanism, for a
generic A/B interface, excited with only four photons, in
a slow motion representation way [SI-1].
The interface energy band bending is not frequently
considered on photovoltaic artificial experiments and
conclusions [16-21,27-29]. Without the energy band
bending there is no interface electric field. Without an
interface electric field (both, EiA and EiB, in Figure 2),
(e–, h+) charges do not get separated. Note that energy
band bending and Fermi level movement follow each
other [10]. On nanostructured materials their size is too
small to consider diffusion controlled mechanism [10,
16-22]. Carriers’ diffusion length on bulk materials is
many orders of magnitude of that of the size encountered
on nanosized materials [10,22]. In this way the charges
separation explanation and the charges displacement di-
rection are not physically correct in many published pa-
pers [16-21,27-29]. On the other hand, the dynamical
bending of the energy bands (and Fermi level), as pro-
posed here, is perfectly in agreement with all physical
concepts, providing the fundamental theoretical explana-
tion on how charges get separated on such systems, as
detailed below for TiO2/II-VI and II-VI/II-VI semicon-
ductors systems [4,10].
To each (e–, h+) recombination at the interface, a
photon of energy h
hSQQ x
    (1)
is emitted (Figures 2 and 3). S is the overlap of the
energy bands of the A and B materials without excitation,
i.e. in the flat band configuration (Figure 3); Qe is the
electron energy quantization within the interface quasi-
triangular shape quantum well; Qh is the hole energy
quantization within the interface quasi-triangular shape
quantum well and Ex is the electron-hole excitonic in-
teraction energy. Note that h
i, the interface energy
emission, is always lower than both A and B band gap
materials. So, material B band gap energy > h
i < mate-
rial A band gap energy. This can explain many lower
energy peaks on composed type II interfaces presented in
the literature, but not understood up to now [16-29]. As
already mentioned, this interface photons emission is
erroneously called charge transfer state [27-29]. But it is
just an interface (e–, h+) recombination and emission.
This energy is lost but it is at the origin of the band
bending and interface electric field.
Figure 3 represents the energy balance at the A/B sys-
tem when excited by photons with enough energy to
promote electrons from the VB to the CB on both A and
B materials. By exciting the A and B materials, the fal-
ling down of electrons from B to A increases the inter-
face electron density, represented by Qe (negative elec-
trical charges on A). In the same way, the falling down of
Figure 3. Energy balance at the A/B interface. The observed
interface photon emission is represented by h
i, which de-
pends on S, the non excited A/B energy band gap overlap,
the Qe, electron quantized well energy, the Qh, holes
quantized well energy and the Eex, electron-hole excitonic
energy. Note the interface energy band bending depends
equally on the h
, the photon external excitation energy.
Equally, Qe & Qh depend on h
holes from A to B increases the interface holes density,
represented by Qh (positives electrical charges on B).
As a consequence of a high density of opposite sign elec-
trical charges at the interface, a high Qe and Qh inter-
action appears. Note that both quasi-Fermi level should
follows these charges movements [10]. This high (e–, h+)
interaction at the interface, represented by Ex, the exci-
tonic interaction between e– and h+, Ex, is of the order
of few to tens of meV for bulk semiconductor materials.
Ex is of the order of hundreds of meV for organic mole-
cules [10,22]. This Ex physical energy parameter for (e–,
h+) interaction (but seated on different materials) gener-
ates a strong interface emission (electrical charges wave
function barrier penetration or tunneling). It is important
to register that the Ex value have never been presented
in the literature for (e–, h+) pairs seated on different ma-
terials, for type II (staggered) interfaces recombination
and emission, represented by h
i [10,22].
Note that the falling down of e– and h+ to the nearby
material should move quasi-Fermi level meanwhile band
bending takes place. Electrons leaving material B (Figures
2 and 3), the quasi-Fermi level should go down on ma-
terial B. Holes leaving material A, the quasi-Fermi level
should go up on material A [10]. Both Qe and Qh cre-
ate an interface electric field from the material B to the
material A. It has the same direction of both EiA and EiB
on Figure 2. Note also that the Fermi level (no excitation,
Figure 1) depends on the materials doping conditions
Copyright © 2012 SciRes. WJNSE
and the quasi-Fermi levels depends on doping and exter-
nal excitation (Figures 2 and 3) [10]. This question will
be discussed below for the AlInAs/InP system and pre-
sented at the support information 1 [SI-1].
Figure 4 represents an A/B interface composed by a
staggered excited system, with both exponential (quasi-
triangular) shape quantum wells for electrons (material A)
and holes (material B). The wave functions probabilities
for the (e–, h+) pairs are equally represented. Calculus
(Support Information 2 [SI-2]) were performed for the
InP/AlInAs system and based on physical parameters
available in the literature [23]. Details of the calculus for
the (e–, h+) wave functions overlap, energy band bend-
ing and existing electric field at the InP/AlInAs interface
is presented elsewhere [23, 30 and in SI-2]. In this work
(Figure 4) the energy bands are modelled as exponential
bended bands, leading to Bessel wave function for carri-
ers. Energy levels of carriers at valence and conduction
bands, as well as the penetration depth, for each kind of
carrier are obtained by solving the transcendental equa-
tion obtained for wave function continuity at the inter-
face. Note in Figure 4: electrons have one and holes have
two wave functions probabilities representation. The
wave function probabilities with about 2 nm and 1 nm of
barrier penetration, respectively for e– & h+, are repre-
sented in this Figure 4. Both barriers wave function
penetration are enough to explain the strong interface
photons emission discussed below and presented on
Figure 5. The barriers wave function penetration and the
strong interface emission observed by the authors and
many others research groups corroborate our comments
on type II interface physical parameters [12,19,23-25,
27-29]. Note that this interface quantum controlled me-
chanism (wave function penetration, tunnelling) is valid
for II-VI and for III-V A/B generic materials’ interfaces
Interface recombination is a dynamical quantum proc-
ess and a very efficient emission mechanism. As the light
excitation intensity upon the system increases, the elec-
tron cascade from upper to lower CBs energy levels, en-
hancing the band bending effect. So, the interface emis-
sion is liked and responsible for the CB and VB energy
band bending and it is also associated to the spent energy
for the charges separation, represented in Figure 2. The
falling down of electrical charges at the staggered inter-
face creates the band bending on both sides of the A/B
system (Support Information 1 [SI-1]). The charges fal-
ling down increase Qe and Qh values and the interface
emission. As a consequence there is also an increase at
the quasi-triangular shape well deepness (represented by
the energy band bending in Figures 2 and 4) at the same
time. By increasing the well deepness, it increases the
interface PL intensity and broadens the interface peak
emission, h
i. It also increases the (e–, h+) wave function
barrier’s penetration and tunneling. The intensity and
broadness of the interface emission, as discussed below,
occurs due to the lack of QM selection rules. The inter-
face light emission is a very efficient (e–, h+) recombine-
tion mechanism [23-25,27-29]. Note that the effect is
double on each side in both sides (leaving e– and receiv-
ing h+), increasing band bending (or increasing the in-
terface electric field EiA & EiB). The low efficiency of the
presented model for charges separation mechanism cor-
roborates and can explains the low efficiency of natural and
artificial systems (1% - 6%). This is the reason for most of
the photons energy loss at the interface and the movement
Figure 4. A/B material excited interface, presenting the CB
band energy bending for electrons and its quantum well
energy levels, and the VB band energy bending for holes
and its quantum well energy levels. X represents the dis-
tance from the interface in nanometer (nm); h
i, the photon
interface emission following the (e–, h+) interface recombi-
nation; and P(x), the (e–, h+) wave function probability to
be found on A or B. Note there are two holes wave function
probability for the conditions we use for the simplified cal-
culations [30 and SI-3]. As the energy band bending de-
pends on the photon energy excitation, many energy levels
are expected on these wells, owing to the spectral FWHM
width presented in Figure 5 (34 to 36 meV at 77K). The P(x)
value penetration for holes on A is about 1 nm; for electrons
on B it is about 2 nm. These values are enough to account
for the interface intense emission PL peaks observed in
Figure 5 (1.303 and 1.193 eV). Similar results are presented
on references [23-25,27-29].
Copyright © 2012 SciRes. WJNSE
Figure 5. 77 k photoluminescence (PL) intensity (I) versus
wavelength experimental results of an InP/AlInAs/InP (A/B/A)
energy staggered interface. Both interface emissions (1.303
and 1.193 eV) are very intense and broad, compared to the
bulk InP (1.395 eV) and bulk AlInAs (1.499 eV) emissions.
These InP and AlInAs PL emissions are observed due to the
ternary layer thickness (1.6 µm), above the carriers mean free
path diffusion length (allowing AlInAs CB-VB transitions and
observation) and the binary layer thickness top layer (0.1
µm, allowing InP CB-VB transitions and observation)
[9,23,24]. Both materials are intrinsically n-type doped
(AlInAs ~1016 at/cm3, InP ~1015 at/cm3).
of few e– and h+ away from the interface (in opposite
directions). Moreover, it is a quantum-controlled system
as it will be exemplified below, for inorganic/inorganic
A/B systems, and as proposed for the photosynthesis
modern experiments.
In conclusion for this section, the necessary physical
tools to separate e– from h+ and recombination at a type II
interface energetic configuration is presented. It is based
on an existing energetic configuration, already described
for inorganic materials. Whenever electrons jump from
material B to material A (Figures 1-3), they leave mate-
rial B under excess of holes and under electronic non-
equilibrium condition. This non-equilibrium condition
moves the quasi-Fermi level down and conduction band
moves up on material B. Whenever holes jump from a
material A to a material B, they leave material A under
excess of electrons and under electronic non-equilibrium
condition. This non-equilibrium condition moves the quasi-
Fermi level up and the valence band down on material A.
Most of the excited A/B interface charges recombine when
jumping, but this event has created a gradient in the elec-
tric potential and an interface electric field. As the jumped
charges are lost and emitted as h
i, their act promotes the
necessary condition to separate few non-jumped electrical
charges. In this case we have both physical tools to sepa-
rate e– from h+: the electric field and the spent energy,
without violating physical laws.
5. Application to the InP/AlInAs/InP Staggered
The III-V semiconductors can be easily grown through
the metal-organic chemical vapour phase (MOCVD)
technique [9,23-25]. The InP/AlInAs system has a stag-
gered energy band gap relative position [7,9,23-25]. As a
staggered A/B system, it presents an interface h
i strong
emission. The A and/or B band gap emission observation
(bulk material) depends on the layers thicknesses, when-
ever A/B interface is grown. For an InP/AlInAs thin film
thicknesses (below carriers diffusion length << 1 µm),
the optical response presents only the interface emission,
which energy is about 1.193 eV [9,23,24]. For thicker
films (above carriers diffusion length, 1 µm), the inter-
face emission is still the predominant optical phenomena.
Figure 5 presents the photoluminescence of an InP/
AlInAs/InP system, where two staggered interfaces are
present. The one called direct: AlInAs grown on InP
(with a 1.193 eV emission peak) and the one called inverse
interface (InP grown on AlInAs, 1.6 µm thick, with a
1.303 eV emission peak) [9,24]. Both interface peaks’
emission are broad (34 - 36 meV at 77 k and 70 - 80
meV at 300 K) and intense, characteristics of type II in-
terface emission. These broad energy peaks are related to
the Qe and Qh available energetic states presented in
Figures 3 and 4 and Equation (1). As (e–, h+) are located
in different materials, the recombination occurring at the
interface takes place free of any quantum mechanical k
selection rule (k = momentum), following the lack of
lattice periodicity (e– and h+ are seated on different ma-
terials). This fact improves the probability of recombine-
tion, making it a more efficient mechanism, as observed
in Figure 5.
As the MOCVD growth conditions does not allow
ease change from As to P chemical elements, the InP
growth on AlInAs possess a much wider transition inter-
face and, consequently, the bands offsets are not the
same as for AlInAs grown on InP. The inverse interface
has an InAsP (about 6 nm) transition layer, as stated by
Auger spectroscopy [9]. These results proof, even with
non-optimised (non-abrupt) staggered interface, the in-
terface recombination mechanism is still predominant for
0.1 to 1.6 µm tick AlInAs layers [9,23-25]. For nano-
sized materials these effects should be much more pro-
nounced, as it occurs with TiO2/II-VI semiconductors
materials applied to solar cells research [26-29]. The laser
excited AlInAs/InP direct interface fluorescence, with 1.193
eV energy peak emission, shown in Figure 5, creates the
Copyright © 2012 SciRes. WJNSE
energy band bending on both sides of the interface.
These energy band bending (or varying electric potential)
can be evaluated by solving Poisson’s equation on both
sides of the interface (see support information 3 [SI-3]).
A simple estimation (not shown) for the (e–, h+) dyna-
mic electric field is from 0.4 × 105 V/cm (EiB, material B
= AlInAs) and 1.24 × 105 V/cm (EiA, material A = InP)
To decrease the interface PL (measured at 12 to 77 K)
1.193 eV intensity to zero, an external electric field of
about 105 V/cm should be necessary, represented in Fig-
ure 6 [25,31]. This is the physical condition to cut off
(stop interface emission) the charge falling down to lower
energy steps of the present AlInAs/InP structure. Sur-
prisingly this is approximately the electric field necessary
to decrease to zero the interface emission intensity of a
similar AlInAs/InP structure published by Sakamoto et al.
([25], its Figure 1, PL intensity extrapolated to zero,
plotted as a function of the external applied electric field,
which value is 0.55 × 105 V/cm) [31]. Our PL experi-
ments shown in Figures 5 and 6 are in accordance with
the results of Sakamoto and co-workers and reveal how
important is the existing high value electric field at the
excited type II interface [9,23-25,31]. Note that this elec-
tric field is comparable to the p-n Silicon semiconductor
junction electric field (104 to 105 V/cm) [10]. Attention
should be taken because it is compared to the extrapo-
lated 12 K and 77 K electric field values [25,31]. The error
percentage is low between 12 K and 77 K [10]. Compar-
ing the estimated electric field (caused by band bending
at the AlInAs/InP interface, 77 K) with that of a Silicon
p-n junction ( about 104 - 105 V/cm, at 300 K) it gives an
idea about the dimension of the excited type-II interface
electric field, as exposed in Figure 6 [10,30,31]. This
comparison is proposed only to give the order of magni-
tude of the AlInAs/InP excited interface electric field.
Moreover, the order of magnitude of a light excited
AlInAs/InP type II interface electric field is known for
the first time [10,25,31]. Note that Figure 6 presents
results of the clear proof of the interface electric field at a
type II, staggered excited interface. These EiA and EiB
(Figure 2) interface electric fields, added because they
are in the same direction, issued from CB and VB band
bending (due to the jumping of e– and h+ at the interface)
are responsible by the few others e–, h+ running to the
opposite side of the interface. They are the separated
charges by type II interface (the driving force, F & F+
represented in Figure 2).
As it will be mentioned below, to the staggered model,
applied to organic molecules (chlorophyll in leaves, for
the photosynthesis mechanism), the interface dynamic
electric field should be much more pronounced because
of the nanometer size dimension and distances within the
Natural system in plants. Note that electric field depends
~0.55 × 105
0.2 0.4 0.6
(× 105 V/cm)
Figure 6. Top: explored structure. Botton: PL intensity (I)
versus external applied field. Experimental results on type
II interface emission (1.2 eV, at 12 K) for an AlInAs thin
layer (100 nm) grown on InP. The PL peaks were withdraw
from [23-25]. Applying an external electric field to the
structure (Eex), the interface emission (h
i) reaches zero
intensity. For this structure, as the AlInAs thickness is be-
low the charges diffusion length, we observe only the inter-
face emission peak; InP and AlInAs peaks are very low
intensity. This experiment shows that energy band bending
gives rise to the interface electric field (Ein), able to separate
e from h+. Application of an external electric field (Eex) to
the AlInAs/InP structure, the 1.2 eV interface emission goes
to zero with Eex ~0.55 × 105 V/cm (Eex cancel Ein) [25]. This
is the clear proof of the interface electric field (Ein) related
to the potential variation (band bending) and interface
emission. Note that the 1.2 eV interface emission peak
moves to lower energy as Eex increases, as Qe and Qh
decreases (Equation (1) and [25]).
inversely on the square of the distance between two elec-
trical charges. These results are applied to organic systems,
as already published, to produce type II energetic inter-
faces for LEDs and organic solar cells, discussed below.
Fortunately, recent publication on organic LEDs and
organic solar cells use experimental results of type II
interface. Unfortunately energy band bending is not fre-
quently applied to organic devices. In contrast, natural
photosynthesis models fail on scientific physical basis
Copyright © 2012 SciRes. WJNSE
without the use of staggered configuration. It fails too for
energy band bending for the charges separation mecha-
nism, by using the flat band condition. The broadness of
interface emission will be discussed below.
In conclusion for this section, we show an AlInAs/InP
staggered inorganic system that, under optical excitation,
creates an interface electric field that can be cancelled by
an external electric field of about 105 V/cm. The interface
emission presents a very intense and broad peak. The
high intensity coming from the lack of quantum mecha-
nical selection rules, as yet discussed above. The opti-
cally created interface electric fields (EiA + EiB) are re-
sponsible for the very inefficient charges separation mech-
anism on type II systems.
6. The Interface TiO2/Material and
II-VI/II-VI Staggered Systems
In this item we present some comments on published
results on TiO2/(B materials) and on (A:II-VI)/(B:II-VI)
interfaces. We show why the published articles do not
represent the real physical situation for charges separa-
tion, although the experimental results are very important.
The lack of correct physical situation, mainly represented
by the absence of an electric field to separate e– from h+,
corroborates to the presentation of the electrical current
across the system without a true scientific support.
TiO2 is a semiconductor material which energy band
gap ranges from 3.1 to 3.4 eV, depending on the physical
phase and crystal quality. The TiO2 anatase phase is one
of the most applied to photovoltaic experiments [11,
16-21,32-34]. Recently a huge amount of experimental
work has been performed on the TiO2/II-VI system com-
pounds [16-21,26,32,33]. Between these systems it can
be found nanomaterials such as TiO2/(CdTe, CdS, CdSe),
TiO2/metals, TiO2/oxides, TiO2/organics, CdSe/CdTe, etc
[8,11,16-21,26-29,32-34]. Most of these recently pub-
lished work on the nanosized systems of TiO2/material
and CdTe/CdSe use the flat band gap energy configure-
tion, presented on Figure 1, for nanomaterials photo-
voltaic experiments (under light excitation) [16-21,26-29,
32,33]. According to their represented flat band configu-
ration, the photon excited electrons move from the mate-
rial B to the material A (TiO2) (Figure 1). In the same
configuration of Figure 1, holes fall down from material
A to B. Unfortunately, these electrical charges (e–, h+)
movements do not describe the actual net charges move-
ment to achieve the generated photocurrent [4-7,10,12,
16-21,26-29,32-34]. In addition, (e–, h+) fall down at the
interface, energy band bending should be considered to
give the real electrical charges movement direction: or-
dinary semiconductor physics theory and experiments are
not considered by these authors [4,10]. The interface (e–,
h+) falling down of carriers and their recombination at
the interface are not considered [4,7,9,10,12,23-25].
These interface (e–, h+) recombination decreases photo-
voltaic efficiency and, mostly, it is not reported because
it is not understood. In summary, are absent: the electric
field, able to separate electrical charges and the spent
energy to perform this process.
The II-VI/II-VI systems, presenting type II interface,
have been applied to photovoltaics, as it occurs with
CdTe/CdSe nanocrystals, in which an interface energy
emission of 1.5 - 1.6 eV has been observed and errone-
ously attributed to “charges transfer states” on photovo-
ltaic experiments [27,29]. These interface energy emis-
sions are similar to the presented in Figures 5 and 6 (1.2
- 1.3 eV). Unfortunately basic semiconductor physics has
not been considered by these authors, as well as the energy
band bending and the necessary electric field to separate
electrical charges having different polarities [4-7,10,
23-25,27-29,32-34]. Moreover the interface energy emis-
sion is considered a “charge transfer PL peak” without
explaining what does it means [27,28]. Indeed they con-
sider that CdTe/CdSe experiences an energetic driving
force for charge transfer, holes finding lower states in the
CdTe and electrons occupying lying CdSe states [29].
And more, it is considered that carrier extraction is driven
not by means of a built-in electric field from a depletion
region due to substitutional dopants; rather extraction is
primarily caused by direct diffusion as dictated by type II
heterojunction [29]. These conclusions show clearly the
misunderstanding of type II interfaces. Note that the 1.5 -
1.6 eV CdTe/CdSe interface peak is broad and symmetric
[27,29]. The same characteristics are present on the
AlInAs/InP, as presented in Figures 5 and 6.
Strictly speaking, photovoltaic TiO2/materials and II-
VI/II-VI electrical charges movement directions’ inter-
pretation is not correct for the recent nanomaterials expe-
riments [16-21,27-29]. The same problem occurs with
photovoltaic artificial nanostructured materials and should
be interpreted as well as for leaves from plants [2,15,
16-21]. For plants, the staggered energy configuration is
not considered. For the artificial TiO2/materials or II-
VI/II-VI systems the energy staggered configuration is
considered, but not the energy band bending configura-
tion for the excited system. Indeed, the molecules’ en-
ergy interface band bending is neither considered for
plants, representing a non-physically and a non-scien-
tifically sustained condition. Moreover the dynamic elec-
tric field at the materials’ interface (TiO2/materials and
natural systems) should jump from 104 - 105 V/cm for 1
µm length ordinary silicon p-n junctions to much higher
values for the nanometer scale of inorganic (TiO2/ma-
terials or II-VI/II-VI) and/or organic molecules inside a
leaf [10,27-29,32-34].
This electric field value represents a huge change
within the photosynthetic artificial and natural world, not
considered up to now. As mentioned above, to cancel the
Copyright © 2012 SciRes. WJNSE
interface electric field of a light excited AlInAs/InP stag-
gered system we need an external electric field about
0.55 × 105 V/cm [25,31]. These physical principles rep-
resent a just known simple semiconductor interface phy-
sics, not considered up to now [4-10,12,23-25,31].
In conclusion to this section, type II interface, applied
for TiO2/(B material) and A:II-VI/B:II-VI systems, uses
the right energetic configuration but do not propose the
necessary physical tools to separate electrical charges
under attraction: the electric field (issued from the energy
band bending) and the spent energy (issued from inter-
face recombination). The flat band representation for
excited systems does not hold on physical basis. Under
photons excitation, the jumping of charges to the nearby
material brings the near interface to a non-equilibrium
condition on both A and B material’s electronic structure
and, consequently, it brings the energy band bending (or
potential variation) and the Fermi level movement (dyna-
mic process). The interface recombination is erroneously
attributed to “charge transfer states” that is not under-
stood by the authors of the present work. Charge transfer
states are confused with interface recombination and
emission, related to the spent energy (loss) to separate e–
from h+.
7. Why Is the Interface Emission So Broad
In our model, the interface emission comes from two
quasi-triangular quantum wells, representing energy states
within Qe and Qh (Equation (1) and Figure 7). As the
deepness of these quantum wells depends on the number
of charges jumping to the nearby material and these
numbers depends on the number of arriving photons, the
emission peak (h
i) will depend on both terms Qe &
Qh. Moreover, without QM selection rules, charges on
each energy level on Qe is supposed to recombine with
charges on each energy level of Qh. It gives rise to the
broad interface emission. Note that Ex (excitonic attrac-
tion, Equation (1)) should also be dependent on the opti-
cal excitation intensity and on Qe and Qh.
As guidelines for type II interface properties, the main
characteristics of type II interface can be summarized as
1) It is a very efficient (e–, h+) recombination quan-
tum mechanical mechanism (but with no QM selection
rules). Note: e– mobility >> h+ mobility, able to allow an
interface permanent e– population inversion;
2) It is a very intense and efficient photons interface’s
3) It has a very broad interface emission peak: h
i =
S + Qe + QhEx (these quantities are explained on
Figure 7). Note that the peak broadness, FWHM
f (ex-
citation intensity and excitation wave length);
emission = hv
S + Q
+ Q
- E
Material A Material B
is possible
Figure 7. Representation of the main characteristics of type
II interface emission: two quasi-triangular shape quantum
wells (QW) are present on opposite side of the interface and
the energy levels in these QW. The luminescent interface
peak is large and intense due to: (a) (e– & h+) are localized
on two different materials on quasi-triangular shape quan-
tum wells, on both sides of the interface; (b) The deepness
of both A/B materials’ interface quantum wells, Qe + Qh,
depends on the excitation density (number of arriving pho-
tons); (c) Absorption and emission by the interface are pos-
sible; (d) The excitonic interaction (Ex) and the e– & h+
wave function overlap should also depend on the excitation
density. Note that the lack of quantum mechanics selection
rules for (e–, h+) recombination at the interface is a conse-
quence for both (e–, h+) seated on different materials (no
4) It is a symmetric emission peak (related to the den-
sity of states in two quasi-triangular quantum well). Note
that pure CB to VB transitions show a non-symmetric PL
peak due to the non-symmetric density of states on their
respective bands [10,22];
5) It has an energy emission with a below both A & B
materials band gap emissions (red shift);
6) It is related to the spent energy (waste) to create en-
ergy band bending at the A/B materials’ interface;
7) It can be associated to FRET or GFP (proposed as
an energy interface emission, instead) [SI-3];
Copyright © 2012 SciRes. WJNSE
8) It can be associated to the charges separation mech-
anism (electric field and spent energy to separate e– from
9) Note that absorption/emission by a type II interface
cannot be discarded. In this case, a VB excited electron
can jumps directly from a material to the nearby material.
In this case, excitation/emission can be at or near the
same wavelength. A question mark comes about: could it
be possible that specific molecules do not present absor-
ption peaks caused by this effect (absorption and emis-
sion at the same wave length)?
10) It can be related to the low efficiency (1% to 6%),
obtained for photovoltaics using type II interface systems.
It is a very efficient way to waste photon energy at the
interface (maybe ~70% of the absorbed photons on leaves
for the visible spectral region).
In conclusion to this section, type II interface recom-
bination/emission has not yet been correctly used to ex-
plain many physical aspect related to photovoltaic sys-
tems. The main properties: intensity, broadness and sym-
metry of its emission peak have not been considered by
the majority of the artificial photovoltaic community. The
broadness of the interface emission is due to the many
energy levels (quantum confinement) on the CB, avail-
able to the many energy levels available at the VB, with-
out rules for their recombination. The interface recombi-
nation remains a quantum mechanics mechanism even if
the transition/recombination from e– and h+ located on
different materials do not need to follow QM selection
8. Energy Staggered Band Gap Configuration
Proposed to the Photosynthesis First Step
Mechanism (Charges Separation and Spent
As already described, the “ground state energy” configu-
ration for two A/B materials does not represent any actual
physical energetic configuration [13,15]. Nature has cre-
ated energetic steps for charges travelling from one to
another different material [4-11]. It represents general
rules for A and B organic and/or inorganic materials. For
molecules from plants (e.g., carotene, chlorophylls), A/B
represent an organic/organic energetic interface. May be
the staggered configuration on organics/organics materi-
als interface is unknown for many researchers. Experi-
mental results on energy band bending are now available
[35,36 and references therein]. Organic molecules band
bending has been mentioned in published articles and
charge transfer modify the energy level alignment [35-
38]. It cannot be considered as a controversial subject
because it is based on experimental results. Moreover,
when electrical charges jumps from a material to its
neighbour, both electronic structures change, otherwise
there is violation of physical laws. So when electrical
charges move from a molecule to another, the energy
band bending is unavoidable. This band bending repre-
sents the necessary electric field to separate electrical
charges of different polarities. The interface jumped e–
and h+ are under excitonic attraction and they can re-
combine emitting h
The amount of published articles on photosynthesis,
considering the physically non-existing “ground state
energy” (GSE) configuration is huge up to now [13,15].
Even for initially considered type II inorganic interface
(CdTe/CdSe), the authors turn to the ground state energy
to try to explain their results, which is an erroneous action,
to explain the charges separation in their system, using
GSE model [27-29]. This GSE energetic configuration
suffers with two main drawbacks, bringing to an uncom-
fortable scientific situation about the non-existence of the
energy band bending between two light excited A/B or-
ganic materials. If the energy band bending is not con-
sidered, the near interface electric field does not appear
[4,10]. Indeed the driving force to separate (e–, h+) elec-
trical charges is absent within the currently accepted
photosynthesis mechanism model [13,15]. But experi-
mental and theoretical work has shown the opposite and
band bending should be considered [11,35-38].
The electronic states of Donor/Acceptor interfaces and
the simplified HOMO/LUMO diagrams presented in the
literature have generally been described, considering the
electron donor and electron acceptor components in their
isolated form [13,15]. However it neglects the specific
electronic interaction at the Donor/Acceptor interface
related to electronic polarization effects (expected to be
different at the interface from the donor or acceptor bulk
material) and possible charge transfer from donor to ac-
ceptor molecules [35]. However if charges transfer is
universally accepted (this the origin of photovoltaics),
why the interface (e–, h+) recombination of these charges
is not frequently considered? Moreover, if charges transfer
is universally accepted, why it is not recognized/accepted
the electronic non-equilibrium on both sides of the inter-
face? Otherwise violation of physical laws is present and
accepted, behind a supposed “controversial” argument.
The A/B interface recombination/emission can be related
to the spent energy to separate electrical charges from the
interface within organic molecules in plants.
Figures 2-4 represent a proposed scientific physical
energetic configuration to explain the natural photosyn-
thetic first step mechanism. A/B being an organic com-
posed interface. This is the only energetic interface con-
figuration (if excited) able to separate electrical charges
of different polarities (and under attraction) [4,12,23-25,
31]. According to the physical need of electric field to
separate e– from h+, the interface electrical fields EiA and
EiB (Figure 2) support this proposition. Moreover it pre-
sents the driving force and the spent energy for (e–, h+)
Copyright © 2012 SciRes. WJNSE
charges separation. Even in Nature it is necessary to
spend some energy to perform an activity. Most of the
plants on Earth are green colour, but less of them extend
to yellow, brown and red colour intensities, depending of
the internal leaves architecture (physical and chemical
properties) [2]. This molecular architecture is about 1 nm
and, according to this, the presented interface energy
levels should be more pronounced numerically, allowing
much broader interface emission (increasing Qe and Qh
on Figure 3). These A/B interface emissions can be related
to the colours emission seen on leaves. Thus the colour
of leaves should be considered mostly an emission, when
considered the spent energy to separate electrical charges
of different polarities. It means that these emission col-
ours’ should be mostly related to the spent energy per-
forming the first physical step to separate (e–, h+) elec-
trical charges. On plants we have scattering (transmission
and reflection) and emission components [15,39,40]. The
spent energy emission we mention is for the charge sepa-
ration mechanism and not for the total colour of plants.
Indeed blue, green, red colours emissions have been ex-
perimentally observed in plants by many authors [39-42].
Why plants are green is still an open question [41]. There
are many evidences that the green leaves absorb more
efficiently light of green (550 nm) than blue (480 nm)
spectra [42]. The absorbance for the 550 nm range is
50% for lettuce, to 90% in evergreen broad-leaved trees.
Green light is more penetrative (i.e., reach all leaf thick-
ness) than blue or red light, absorbed mostly on the upper
part of the leaf. This is the reason why the green light is
more efficient for the photosynthesis process in plants
[42]. Moreover, if the green colour is more efficient than
blue and red colours, to perform the photosynthesis pro-
cess, why to consider the green colour of plants as a re-
flection [42]? Note that reflection is not considered as an
interaction with the leaves’ molecules. If the green colour
of plants is also presently related to the charges separa-
tion mechanism, few changes in the gene expression
should be operated when leaves molecules have they
environment changed [43,44].
If current natural conditions for plants are to spend en-
ergy mostly on the green colour spectral region, in the
past this colour could be on another spectral region (maybe
red shifted), to account for the huge amount of petroleum
we have today, originating from exuberant forests from
600 - 700 millions of years ago. If sugarcane plantation
in its natural colour (green) can be genetically yellow col-
oured (red shifted), we should have (h
green – h
19%, which represents the energy economy for the sug-
arcane machinery to work out its internal processes and
to produce more biomass and/or sugar. But it is only
possible if the colour can be related to an emission for
the natural photosynthetic mechanism and related mostly
to the spent energy to separate electrical charges.
Breeding plants have other lower intensities for col-
ours emissions [2]. Changing Earth atmospheric condi-
tions (e.g., concentration of CO2, O2, H2O, CH4, NH4,
acids) will determine the plants adaptation for their size,
colour, nutritive power and exchange with the environ-
ment. Indeed, by changing the CO2 (2 × 390 ppm) con-
centration available to the sugarcane environment, it can
be increased by 60% the biomass and 25% - 30% the sugar
content [44]. Moreover gene expression is accordingly
changed [44]. These authors does not mention sugarcane
colour change but they mention the possibility of gene
expression alteration to be related to charges transport
and CO2 assimilation by sugarcane [43,44]. If gene ex-
pression is associated to charge transport, it is surely linked
to the charges separation mechanism, discussed above.
Recently Yen Hsun Su and co-workers, doping plants
(in vivo experiment with Bacopa carolinianais) with gold
nanoparticles, showed that it is possible to change the
colour of leaves to red, yellow or blue, depending on the
excitation light and the gold nanoparticle size/shape [45].
Exciting the Bacopa carolinianais/gold system with
white light they have obtained yellow leaves. Exciting
the same system with UV (285 nm) they have obtained
blue and red coloured leaves. If in Bacopa carolinianais
leaves the green colour is a reflection, due to Chl-a, the
leaves should keep green. It means we cannot extract
Chl-a from leaves and conclude that “plants are green
because Chl-a does not absorbs green light”. Gold
nanoparticles change the Chl-a environment, changing
the emission colour, and the Chl-a is still there. If Chl-a
is still there and we cannot consider the colour as reflec-
tion anymore, what should be the Gold/Chl-a red or blue
colour mechanism: an emission or a reflection?
Other experiment developed by Blitz and co-workers,
by changing lettuces environment, exposing it to more
UV (A + B) energetic light, it was observed the colour
change [46]. Moreover two times more nutritive power
for these UV (A + B) extra-exposed lettuces was observed.
Gene expression change should follows in these experi-
ments, as it is the case of the sugarcane [43,44]. Further-
more on an old article on green fluorescent proteins (GFP),
it is proposed that the two visible absorption bands cor-
respond to “two ground-state conformation” [47]. The
staggered band gap relative position has “two ground-
state like” energetic conformation, as proposed on Fig-
ures 1 to 3. On support information 4, [SI 4], we present
few experiments on plants, showing that leaves have
their internal machinery that transform high energy pho-
tons into lower energy photons (red shift). The absorp-
tion of light and emission at lower energy is proposed to
perform the charges separation process.
Studies with organic LEDs and organic solar cells ap-
ply the concept of staggered energetic configuration to
produce or to absorb light [48-57]. These organic devices
Copyright © 2012 SciRes. WJNSE
are emitting/absorbing light and replacing solid state
LED/solar cell, respectively. The organic light emitting/
absorbing are composed of tens of nanosized layers of
few tens nanometer thickness. Organic molecules are
diluted in a medium and these molecules touch each
other at the layers’ interface. A. Heeger (2000 Chemistry
Nobel Prize Laureate) used staggered energetic organic/
organic interfaces to produce about 10% efficiency solar
cells [52-54]. The energy peak emission at these stag-
gered energetic interfaces and layers are broad and in-
tense [48-60], a characteristic of type II staggered inter-
face energy emission, as represented in Figures 5 and 6
and discussed above.
In this paper we discuss the band gap energy emission
whenever energetic A/B interfaces are present. As Fluo-
rescence Resonance Energy Transfer (FRET) mechanism
deals with below band gap emission, we will equally pro-
pose few words about the possibility of its explanation be
regarded as type II interface emission. Note that FRET
model is based on classical physics, described/proposed
about 60 years ago by Theodor Forster [13,61]. FRET
model suffers from few drawbacks, considering unknown
parameters, correction factors, intensities corrections, etc
[62,63]. Based on our results, a different model can equally
be proposed to explain the “energy transfer” between two
different organic or inorganic material pairs, based on the
existing and actual band gap energy relative position of
both A/B pairs. According to recent experimental works,
organic molecules present energetic steps (up or down)
for excited electrical charges to travel from a molecule to
another one [48,60]. These energetic steps for electrical
charges flow, from a molecule to a nearby molecule, are
very important and not considered on the FRET theory.
These energetic steps can promote energy interface
emission (red shifted), observed for many published data
explanation. As FRET is a radiationless energy transmis-
sion mechanism, we propose that the actual physical/
optical mechanism can be regarded as a radiation inter-
face emission mechanism, for many systems, based on
type II interface properties. As an example, the applica-
tion of the present proposed model can be applied for
cyanide dyes (Cy3, Cy5) organic molecules [62,63].
When these molecules pairs are placed together, forming
a Cy3/Cy5 interface, an emission peak at 680 nm is ob-
served, when excited with 540 nm light [62 and SI-3].
This 680 nm emission of the Cy3/Cy5 system can be
associated to type II interface emission. In this way,
FRET should deeply be re-discussed as it is based on
classical physics and staggered energetic interfaces are
based on quantum physics.
In this paper, type II interface energetic configuration
and interface emission is proposed to explain electrical
charges separation. It can equally be proposed to explain
many non-comprehensible physical observation like FRET,
GFP, green colour of plants and its colours changes by
changing the proteins environments [48-60,63]. The me-
chanism, based on type II interface, is supported by the
quantum mechanical basis, in contrast to the classical the-
ory used to explain the photosynthesis first step (charges
separation), GFP and FRET. Note that FRET mechanism
doe not separate electrical charges. Only the absorption
of light is not enough to separate electrons from holes. A
question comes about: If FRET is present on the photo-
synthesis process, where is it, the charges separation
Many recent experimental studies propose the photo-
synthesis process as quantum mechanics controlled [64-
71]. Forster’s theory is based on classical physics; more-
over it is based on a non-existing energetic configuration,
as is the case for the GSE representation [4,10,13,15].
Forster theory does not present the necessary electric
field to separate electrical charges. It does not present the
spent energy to perform this process [13,15]. In summary,
the present classical theory violates physical laws, con-
cerning the necessary tools to separate electrical charges
under attraction.
In conclusion to this section, we propose the stag-
gered energetic interface (quantum mechanics controlled)
to explain the photosynthesis, FRET and GFP processes,
instead of the ground state energy (classical physics de-
scription) configuration. The staggered configuration has
been used between organic molecules to produce organic
LEDs and organic solar cells. The staggered configuretion
and energy band bending for organics is a real physical
property and not a controversial language. It gives us the
necessary physical tools to separate electrical charges. If
recent optical experiments propose photosynthesis as a
quantum mechanics controlled, we should look for
quantum physics instead of classical physics. The use of
the ground state energetic configuration, to explain the
photosynthetic mechanism, is a non-sense physical path-
way that should be re-discussed. Under photons excita-
tion, charge’s jumping to the nearby organic molecule
brings the near interface to a non-equilibrium condition,
on both A and B molecules’ electronic structure. The
non-equilibrium brings energy band bending (or potential
variation) and Fermi level movement (dynamic process).
As the A/B generic organic systems are nanometer size
and distances, each (e–, h+) wavefunctions should cross
few molecules under interaction. It is impossible not to
consider this fact on natural systems. Note that the stag-
gered energetic configuration can be present at the same
organic molecule, as it can be for two different molecules.
This molecule can be branched composed, representing
an energetic interface of the three types describe above,
but never with the GSE configuration.
Copyright © 2012 SciRes. WJNSE
9. Application of the Charge Separation
Mechanism: How to Waste the Visible
Light Absorbed Energy by Leaves
Electrical charges separation mechanism is not yet well
understood for photosynthetic natural and artificial appli-
cations. The present preliminary proposition represents a
new regard on the photosynthetic natural and artificial
electrical charge separation mechanism. Considering it as
a new mechanism, most of the parameters necessary to
calculate the efficiency (number of separated charges/
number of photons) are not available. According to the
present model, it can also be applied to other materials
presenting staggered energy configuration, the polymer/
polymer and polymer/inorganic interfaces [49-60]. It can
equally occur with the exciton dissociation transferring a
single charge to the material A, leaving behind an oppo-
site charge in material B [22,34,51]. Excitons from elec-
trical charges seated on different materials are different
from excitons seated within the same material. The authors
are not aware about experimental/theoretical results/
values of excitons when electrical charges of different
polarities are seated on different materials or molecules
[10,22]. The charge transfer (number of charges/number
of photons) for photovoltaics, of about 1% - 6% efficiency,
is easily achieved for nanostructured materials [8,10,
16-21]. The same condition is valid for photovoltaic or-
ganic/organic or inorganic/inorganic solar cells, in which
about 10% efficiency is commonly achieved [10,52-57].
As the material’s properties and its interfaces have an
important role, the present model should be applied and
improved to increase devices efficiency. Note that the
organic/organic interface for LEDs and solar cells uses
the staggered energetic configuration, instead of “ground
state energy” configuration and that this model cannot be
considered as a controversial subject [32-36,49-60].
Concerning the natural photosynthesis, the sunlight
energy absorption and the final efficiency by leaves on
plants seems to be about 5% [1-3,13]. In this way the
application of the present model to estimate the charge
separation efficiency needs new experiments, because
most of the available data concern non-staggered ener-
getic configuration (the GSE one). Moreover the green
colour of plants is considered mostly a reflection. It
should be emphasised that green leaves have also other
minor colours intensity (emission?), such as yellow,
brown and red [2]. If these lower intensity colours repre-
sent also charges separation within a leaf, caused by a
staggered configuration between the energy bands of
leaves’ constituents, the efficiency should be verified in
consequence. When it occurs, the natural leaves’ consti-
tuents should propose many staggered energy configure-
tion. Chl and carotene present 3 - 5 main absorption energy
peaks [2,13,15]. More efforts are needed to find out the
actual energy relative position for each absorption energy
band for the leaves’ constituents. To know their energetic
relative position, more studies are necessary on the band
gap engineering to present the actual energetic configu-
ration and both: charges separation and waste of energy
to perform the job.
Transmittance (T) and reflectance (R) experiments on
leaves, within the 400 to 700 nm spectral region, give
scattering (S) of about 21% (S = T + R), according to
many previous standard experimental results [15,72].
Figure 8 concerns typical reflectance and transmittance
curves for leaves, on the visible (400 - 700 nm) and in-
fra-red (700 - 1000 nm) spectral regions, showing the
necessity for plants to have an efficient way to waste the
sun light energy quickly. Maybe the staggered interface
is the only appropriate candidate. The absorption expe-
riments for isolated Chl-a cannot evidence scientifically
that leaves do not absorb on the green region. They rep-
resent different systems. Moreover transmittance and
reflectance experiments show that leaves reflect on the
green colour about 15%, as presented on Figure 8 [15,
72]. The transmittance is about 30% for the 535 nm
green spectral region. It means the absorbance is about
55% for the green (535 nm) colour region. 15% for the
reflection cannot explain the green colour intensity of
plants. Type II interface can be able to absorb and emit
nearly the same light wavelength [73]. In this case, the
absorption is carried out by an excited electron jumping
directly to the nearby material (VB of B material to the
CB of A material, Figure 3) [73]. The de-excitation of
this electron is followed by the interface emission, emit-
ting about the same colour or energy that is absorbed
(Figures 2 and 4). Note that interface absorption should
create energy band bending on both sides of the A/B in-
According to Figure 8, for the visible region (400 -
700 nm), the area below T and R curves gives scattering
S = T + R = 21%. As % Absorbance = 100% – (R + T),
on average, 79% of the visible spectra is absorbed by
leaves, representing a huge amount of energy that plants
cannot afford. Nature should invent an efficient way to
waste quickly this absorbed sunlight energy. Type II en-
ergetic interface can be a good candidate, wasting it as an
emission, but related to the spent energy to separate elec-
trical charges, a non-efficient quantum mechanism to
separate (e–, h+) electrical charges.
Maybe nature have got the solution and created type II
interface as the mechanism to get ride of most of the 79%
average absorption within the 400 - 700 nm solar range
(Figure 8) [15,72]. So, if natural photosynthesis effi-
ciency is about or below 5% it should be withdraw from
79% absorption, for the 400 - 700 nm visible solar spectra.
Artificial photosynthetic nanomaterials get about 1% - 6%
Copyright © 2012 SciRes. WJNSE
Figure 8. Typical reflectance and transmittance curves for
leaves on the visible and infrared spectral regions, evidenc-
ing the necessity of an efficient way to waste quickly the sun
light energy for plants. Note that there is only 15% of refle-
ctance on the green colour region (535 nm). The R + T value
at the 400 - 700 nm region gives an average absorbance of
about 79%. This is a huge value to be afforded by plants in
hot lands. Average values were obtained from the area be-
low the R and T curves, for the desired spectral region. R +
T is about 98% within the infrared region. There is almost
no absorption for the IR region, for plants. The typical R
and T results are extracted from references [15,72].
efficiency for their transformation from photons to sepa-
rated electrical charges [8,16-20,27-29]. Fig ure 2 and
support information 1 [SI-1] show the interface recom-
bination/emission is a mechanism to get charges separa-
tion [9,12,23-25,30,31]. Moreover, it is not an efficient
mechanism to separate electrical charges, because most
of the excitation light energy is spent as interface emis-
sion. The artificial photosynthetic literature had never
touched and related the interface emission as a conse-
quence of the low efficiency of the explored devices (1%
to 6% efficiency) [8,16-20,27-29]. Here we propose the
interface emission mechanism to account for most of
these low efficiency natural or artificial devices.
In conclusion to this section, according to published
data, natural leaves should absorb about 55% of the sun
green spectra in the visible region. 15% of reflection does
not explain the green “reflection” colour intensity of plants.
As leaves absorbs higher photons energy than the green
photons and emit lower energy photons (green, yellow,
red), to the green colour intensity of leaves it should be
added the green transformed by their internal machinery.
According to the same published data, leaves should absorb,
on average, 79% of the visible sun light spectral region.
This enormous quantity has never been discussed in the
literature and should be able to cook plants in few min-
utes on sunny days. It means that we need a quick and an
efficient optical mechanism to get rid of this cooking
absorbing system. The same consideration is valid for
artificial photosynthetic systems, for which efficiency is
low (1% - 6%). Type II energetic interface and its inter-
face emission is the only possible configuration to solve
the problem: a really efficient way to absorb and waste
photons, meanwhile separating few % of the excited (e–,
h+) charges.
10. Final Considerations and Conclusions
To copy the photosynthetic natural conditions we need to
use existing physical conditions that explain the charges
separation mechanism. Currently natural photosynthesis
mechanism accepted model is not scientifically and phy-
sically acceptable: the energetic configuration does not
hold on physical basis and neither allows the current
physical situation to separate electrical charges with dif-
ferent polarities (or charges under attraction). Artificial
nanostructured photosynthetic materials models suffer
from the same scientific physical drawback: the mecha-
nism to separate electrical charges under attraction.
In few words, both natural and artificial models violate
physical laws if they are not able to present the necessary
electric field (the driving force) and the spent energy to
separate negative (e–) from positive (h+) charges. Cor-
recting these common related drawbacks we can further
improve artificial and natural photosynthetic systems and
get more energy from the free sunlight source. The solar
energy is our only economical pathway if the physical
mechanism underling the 2 - 4 billions years of evolution
is understood: the charges separation mechanism. If
nowadays the solar energy is less efficiently used than in
the past (600 - 700 millions of years ago, with a more ele-
vated CO2 concentration) for the natural conversion into
fuel, we get to a controversial question: is the desertifica-
tion a direct consequence of the CO2 atmospheric con-
centration decreasing (200 - 370 ppm, years from 1850-
2010) [1-3]? If so, the greenhouse effect should be ob-
served differently from current point of view. To this end,
the natural and artificial energetic configuration between
two different materials should be correctly considered.
Excited A/B materials and interfaces can deliver the
necessary driving force to separate electrical charges
charge (charges with different polarities). The currently
defended staggered representation for the II-VI/II-VI and
TiO2/II-VI nanosystems, to separate electrical charges,
does not present any physical support to separate e– from
h+ [16-21,27-29,79-85]. Indeed, these very important
experimental results does not explain correctly how elec-
trical charges flow as they were gravitational-like balls
falling down through stairs [16-21,27-29,73-88]. Unfortu-
nately electrical charges should obey electrical parameters.
Copyright © 2012 SciRes. WJNSE
The misunderstood on electrical charges separation me-
chanism has been propagated for many published results
[27-29,73-87]. Commonly found assertion like “… the
absorption of a photon leads to efficient separation of a
single electron-hole pair” is present in the literature,
without scientific care [80]. The absorption is only the
first step. The subsequent step, to separate (e–, h+), should
spend energy. Interface energy band bending has equally
been proposed erroneously, even using type II interface
to explain electrical charges separation and its flow dire-
ction [74,75]. The staggered energy configuration and its
band bending should be downwards and not upwards as
recently published [74-78]. Basic physical information
on electronics and solid-state physics is available every-
where and has been constantly neglected [4-7,10,22].
Interface emission has been erroneously attributed to
“charge transfer state”, for organic and inorganic systems,
meanwhile it is just a recombination of e– with h+ seated
on different materials [27-29,51,77,88].
Most of the published data and mechanism explanation
uses the flat band configuration to show e– and h+ move-
ments across the interface between an A/B generic inter-
face [13,15,27-29,48,77-88]. This is proposed for organic
and inorganic generic materials [27-29,77-88]. These
published work do not consider the energy band bending
as exposed above and as exposed in many solid state
physics and organic material published data [4-7,9,10,12,
22,36]. The electrical charge jumping from a material to
the nearby material creates an electronic non-equilibrium
on both materials, moving the quasi-Fermi level (up or
down) and, consequently, moving the CB (LUMO) &
VB (HOMO) (down or up) [4,10,SI-1].
In summary, it is proposed a model describing the only
energetic configuration between two different nano-
sized materials, able to provide the necessary electric
field to perform (e–, h+) electrical charges separation on
photovoltaic systems, such as inorganic/inorganic, inor-
ganic/organic and organic/organic interfaces. It is pre-
sented, in these descriptions, many systems in which type
II interface recombination and emission is the most im-
portant electro/optical phenomena: AlInAs/InP, TiO2/II-VI
and II-VI/II-VI. These experimental results have been
linked to organic solar cells and organic LEDs, in which
the staggered energetic configuration is experimentally
already known and applied. We have shown that the opti-
cally excited AlInAs/InP system has an internal electric
field (105 V/cm), issued from the energy band-bending
whenever charges jump to the nearby material. The ground
state energy (GSE) representation, to explain photosyn-
thetic mechanisms, is a non-existing physical energetic
configuration. Charges do not care about GSE, charges
care about energetic steps if the aim is to separate elec-
trons from holes. GSE model does not allow the separa-
tion of e– from h+ because it does not promote the basic
electric field and the spent energy to separate charges
under attraction. Without these two basic physical con-
cepts it is impossible to separate (e–, h+) electrical
charges in nanosized materials without violating physical
laws. Contrary to current believes, charges do not get
separated whenever nanomaterials absorb light. This is
only the first step and it represents an excitonic attractive
entity. The next step, to separate (e–, h+), depends on
energetic configurations under which these charges are
submitted. Diffusion controlled process on nanometric
systems is out of question. Diffusion controlled processes
is for the old generation of silicon devices (about 1 m
diffusion length). The proposed model, based on stag-
gered energetic interfaces and energy band bending, in-
troduces equally the concept of spent energy to separate
electrical charges. The spent energy is related to the in-
terface emission and it can be used to explain most of the
photons emission of absorbed visible sunlight (~79%) by
plants. It is impossible the surviving of plants without an
efficient and quick (optical) way to waste the absorbed
visible light. Moreover, the proposed mechanism is
quantum controlled, as proposed by many recent experi-
mental results on organic molecules. According to pub-
lished data, it was shown that, by changing the plants’
environment, there will be change in the biomass and
nutritive power. Similarly, by changing the leaves’ mole-
cules environment, the leaves’ colour also change. In this
way, the colours of plants can be mostly related to the
spent energy to separate electrical charges. The green
colour being more efficient to promote the photosynthe-
sis process, instead of being a reflection, without rela-
tionship with the process, can be linked to the charges
separation mechanism: it can mostly be linked to the
waste, to perform the process and to protect leaves. The
ideas and results presented here can be extended to other
models or materials/devices as FRET, GFP, CTS, organic
LED and organic solar cells. Human needs to know this
Nature non-efficient charges separation mechanism to
improve its efficiency in natural and in artificial solar
energy production. The energetic staggered configuration
is an appropriate candidate. But it should be worked out
with its intrinsic physical parameters, already described
in the literature, but not correctly considered by many
photosynthetic workers. If worked out correctly, natural
and artificial photosynthetic systems can be adequately
copied/improved. Nature obeys physical principals. Men
should follow this way, in trying to explain natural and
artificial physical mechanisms. Charges separation is a
physical and not a biological mechanism.
11. Acknowledgements
The authors are grateful to the financial support from
ANR-Filemon35-France, and the Fundação de Amparo à
Copyright © 2012 SciRes. WJNSE
Ciência e Tecnologia do Estado de Pernambuco (FACEPE)
and Conselho Nacional de Desenvolvimento Científico e
Tecnológico (CNPq) Brazilian agencies. The authors
thank professors Cid Araújo, Celso P. Melo, Michael
Sundheimer and Dr. Euclides Almeida from DF-UFPE &
UFRPE–Brazil and to Dr. Gregory Smestad (from SOL-
MAT) for valuables discussions and suggestions.
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Support Information
SI-1. Energy Staggered Interface: Electrical
Charge Separation Mechanism
The following slides present how the proposed mech-
anism does work, based on the excitation of one hypo-
thetical interface between (Material A)/(Material B).
This excitation is performed with only 4 photons. It is,
equally, represented why the interface recombination/
emission process has a so large emission peak. The (e–,
h+) wavefunctions penetration is represented for the
AlInAs/InP system. The present SI-1 should be viewed
in a ppt version by clicking below. Figure SI-1-1 repre-
sents energy band bending mechanism. Figure SI-1-2
represents the jumping of charges to the nearby material.
Figure SI-1-3 represents the separated charges and its
catalytic action. Figure SI-1-4 represents the two quasi-
triangular quantum wells at the interface, to explain the
interface emission peak broadness. Figure SI-1-5 repre-
sents the two quasi-triangular quantum wells at the in-
terface, to explain the e– h+ wavefunctions overlap.
The natural photosynthetic first step process is based on
the light absorption and followed by electrical charges
separation on leaves. Only the absorption of light does
not separate e– from h+. The absorption of light creates
(e–, h+) pairs. For the separation we need an appropri-
ated energetic configuration.
The present existing Forster’s model, to explain the
photosynthetic first step process, is based on classical
physics. The same ideas are applied to artificial systems.
The present accepted model violates mainly three physi-
cal laws.
1) The energetic configuration, that represents the en-
ergy transfer from a molecule A to a nearby molecule B,
does not exist in physics (the ground state energy repre-
sentation). Charges do not care about the ground state
energy configuration. Charges care about energetic steps
(up or down).
2) To separate negative from positive charges, the
necessary electric field is not present. The absorption of
light does not separate electrical charges. This is just the
first step of the process. To do the next part we need an
appropriate energetic configuration that allows the appa-
rition of the electric field. This electric field must come
from a varying potential.
3) To separate electrical charges under attraction we
must spend energy. Note that the excitonic attraction
energy between e– and h+ on organic molecules is about
10 to 50 times that ones present on inorganic materials.
This means that we need a much stronger electric field
for organics, to separate (e–, h+). Moreover, recent papers
(about 10), published in Nature, Science, PRL, (see text),
show evidences that the photosynthesis first step mecha-
nism is quantum mechanics controlled.
The enclosed and proposed mechanism does not suffer
from these drawbacks (1 to 3). It is a photonic quantum
mechanics mechanism.
Click here to see the ppt slow motion model.
Note: the ppt pictures were prepared in a Machintosh
computer. Version:
SI-2. Mathematics Calculus (Wavefunction,
Probabilities Densities)
The following pages present details of the calculations
Figure SI-1-1. Representing the energy staggered interface: electrical charge separation mechanism. How does the energy
band bending arrive at the energetic interface? The flow of charges from one material to the nearby material creates an elec-
tronic no-equilibrium on both materials, near the interface. This electronic non-equilibrium creates potential variation. It
creates the necessary electric field to separate charges: e– from h+.
Copyright © 2012 SciRes. WJNSE
Figure SI-1-2. Representing the energy staggered interface. It represents the charge separation mechanism in a picturial slow
motion maner. Excitation of such an energetic structure with only 4 photons.
Figure SI-1-3. Representing the energy staggered interface: charge separation mechanism applied to photosynthetic first step
processes. Note the hudge electric field crossing the interface for the AlInAs/InP system (see text). For organic molecules, this
electric field should be much higher since the excitonic attraction is much higher than for inorganic materials.
Why is the interface emission peak so large? See it in the nexts slides…
Figure SI-1-4. Representing the interface physical parts linked to the interface emission peak. All the terms of the equation
below should change with the excitation intensity. Mainly Qe + Qh should change more than the others terms. This explain
why the interface PL & EL emission peaks’ are so large.
Copyright © 2012 SciRes. WJNSE
Copyright © 2012 SciRes. WJNSE
Figure SI-1-5. Representing the interface physical parts linked to the interface recombination/emission peak. The interface
recombination and emission depends on the e & h+ wavefunctions’ interface overlap. The 1 to 2 nm wave-function
penetration is for the AlInAs/InP system (see text).
for the probability density and the (e–, h+) wavefunction
overlap at the AlInAs/InP interface. In this work the bands
are modelled as exponential bended bands, leading to
Bessel wavefunctions for carriers. Energy levels of car-
riers at valence and conduction bands, as well tunnelling
length, for each kind of carrier are calculated by solving
the transcendental equation obtained for wave function
continuity at the interface. Parameters for the present
calculation were taken from reference. Abraham, P. et al.
Photoluminescence and band offsets of AlInAs/InP.
Semiconductor Sci. Technology 10, 1-10 (1995) [23].
The photon excited staggered AlInAs/InP interface gives
rise to an interface electric field of about 105 V/cm. This
is approximately the same value obtained for the ex-
perimental result of Figure SI-2-1 (see text). The calcu-
lated e– wavefunction penetration on the AlInAs material
is about 2 nm. The calculated h+ wavefunction on the
InP material is about 1 nm. Both values account for the
interface (e–, h+) recombination and interface intense
Figure SI-2-1. The scheme of tilted electronic bands for
These equations are applied to both the calculation of
energy levels for the holes in the valence band and for
the electrons in the conduction band. In each case we
should observe the proper values of the parameters of the
Table 1. Using the transformation of variables
Both bands of valence and conduction bands have similar,
bent on account of them injected carriers. In each of the
potential will be approximated by exponential functions as
shown in Equation (1) and picture in Figure SI-2-1. /2
ξσ δe
ξη e
VxV δex
Vx Vex
 
 
Substituting these potentials in the Schroedinger equa-
tion we have:
We get the following equations:
dd 40 0
dd 40 0
 
 
d2 1 0
d2 Δ 1 0
ψmEVe ψx
 
 
These are the known Bessel equations in which it is
defined the parameters:
The solutions for the Equations (4) will be:
 
AJ 0
BI 0
 
 
These solutions must satisfy the boundary conditions
at x = 0. Equating the functions and their derivatives at x
= 0 results the transcendental equation:
J2 I2
vvv u
 
 (7)
The probability density is represented by
 
x (8)
The parameters concerning the potential wells in the
conduction band and valence are those given in Table 1.
Solving the transcendental equations for the valence
and conduction bands it was obtained two energy levels
for holes (VB) and one energy level for electrons (CB) in
the conduction band. The energies and the parameters
that determine the wave functions for electrons and holes
are given in Table 2 and the density probabilities are
represented in Figures SI-2-2 and SI-2-3.
SI-3. Fluorescence Resonance Energy Transfer
(FRET), Presented as Type II Interface Emission
The following pages present how the proposed mecha-
Table 1. Parameters for the potential wells.
(nm) me
0 349 60 20 5 5 0.07
0 272 60 20 5 5 0.4
Table 2. Energies and parameters determining the wave
functions for electrons and roles.
A B E (meV) V1-E(meV)
Electrons 0.491 804.794 54.68 5.32
1.223 5.313 × 10538.85 232.68
0.689 9.9 × 104 56.13 215.87
nism does work for FRET. Fluorescence resonance en-
ergy transfer (FRET), is a physical phenomenon by
means of which electronic excitation can pass from one
chemical unit to another, following the absorption of
light. The chemical unit we are discussing here is only
for chromophores. In this support information, FRET is
observed as a type II interface emission and not as an
energy transfer from one material to the nearby material.
It is presented just one example for organic cyanine dyes
molecules. The same idea can also be applied to green
X (nm)
AlInAs/InP interface
Figure SI-2-2. It shows the probability density versus dis-
tance within the structure, for the valence band and con-
duction band, where we see that the penetration probability
for electrons and holes beyond the wall of the well. The
region with interpenetrating wavefunctions is pointed out in
the figure by pink colored rectangle.
gap energy
-20-12-4 0 4 122
X (nm)
AlInAs InP
Figure SI-2-3. It shows schematically, with the values of the
energy-scale the probability densities for electrons and
holes relative to the potential wells within the system
AlInAs/InP. X (nm) is the distance from the interface.
Copyright © 2012 SciRes. WJNSE
fluorescent proteins (GFP) as well. These ideas are pre-
sented on Figures SI-3-1, SI-3-2 and SI-3-3. They have
the explanation text for each one figure.
SI-4. Experiments with Leaves
The following pages present how the proposed mecha-
nism does work for leaves from plants. This SI presents
experiments with leaves, showing their internal trans-
formation machine, absorbing higher energy photons and
× ×
Figure SI-3-1. Representation of an A/B type II generic
interface, showing the motion for the energy band bending
and the quasi-Fermi levels displacements, whenever the
A/B system is excited by photons which energy is higher
than both A & B materials’ band gap. At the interface, the
energy staggered interface (type II): electrical charge sepa-
ration mechanism, by an existing interface electric field.
This electric field comes from a varying potential, which
origin is from the energy band bending at the interface.
Whenever charges jump to the nearby material, the elec-
tronic environment is changed in both materials. This
change creates the potential variation and the interface
electric field. This interface and its properties are applied to
explain FRET.
Figure SI-3-2. Intensity (I) versus wavelength (
) for optical
properties of cyanides molecules. Representation of the
absorption (A) and emission (E) regions for Cy3 & Cy5
organic cyanine dyes [62,63]. The dashed common region
represents the overlap between the Cy3 emission region and
the Cy5 absorption region of these molecules. Following
FRET mechanism, the common A & E region for both
molecules allows the Cy3 molecule be excited on the 525 -
550 nm region and the Cy5 molecule to emit within the 670
- 700 nm region. This red-shifted emission is proposed to be
type II interface related in the next Figure SI-3-3.
emitting lower energy photons. Leaves are considered to
have about 1 nm size proteins, separated by about 1 nm
distance. These dimensions give about 1020 energetic
interfaces/cm3. This is above the doping density (1017 to
1018 atoms/cm3) for inorganic semiconductor optical de-
vices or organic optical devices. These numbers show
that interface must be taken in to consideration if absorp-
tion/emission mechanisms are discussed for leaves.
We performed optical absorption (Figure SI-4-1) and
Copyright © 2012 SciRes. WJNSE
Figure SI-3-3. Representation of a type II interface. Instead
of FRET, it is explained by energy staggered configuration
interface emission. 540 nm is related to the external excita-
tion energy. 680 nm is related to the interface emitted en-
ergy. 590 nm is related to the Cy3 main bandgap energy
and 670 nm is related to the main Cy5 bandgap energy.
Organic cyanine dyes: Cy3 = A and Cy5 = B [62,63]. Note
that the present proposal (type II energetic configuration)
does not need momentum conservation, as is the case for
FRET. Symmetry (QM selection rules) does not apply since
both e– & h+ are seated on different materials when they
photoluminescence (PL, Figures SI-4-2 and 3) experi-
ments on leaves (Erytrina indica picta) at room tem-
perature, to see if there are emissions from them. These
leaves are naturally composed of green and yellow re-
gions (Figure SI-4-1). We used intact young yellow-
green Erytrina indica picta leaves exposed to green (532
nm) and violet (386 nm) laser light excitation. The
leaves’ regions exposed to these excitation wavelengths
resulted in broad-band light emission on the blue, green,
yellow and red spectral regions.
Figure SI-4-2 presents the PL experimental results for
the 532 nm excitation, by using a 512 - 560 nm filter for
detection and avoid the excitation peak. The green part
of the leaf presents a broad peak at the red side of the
spectrum (675 - 825 nm). The yellow part of the leaf pre-
sents two main peaks (orange colour line) between 560 -
Figure SI-4-1. Represents the absorption x wavelength for a
leaf, measured at room temperature. This is the usual be-
haviour for natural leaves, with a deep within the green
surface of the leaf, at the green spectral region. The deep
within the green spectral region for green leaves is attrib-
uted to chlorophyll no absorption. Note that the yellow part
of the leave presents no deep within the green spectral re-
gion (535 nm) and chlorophyll is still there. Above 700 nm
excitation there is practically no absorption. This figure is
to be compared to Figure 8 within the main text. Base line:
air, Equipement: Cary 50E.
750 nm. So, the 532 nm excitation gives red shift light e-
mission on both regions.
Figure SI-4-3 presents the leaf excitation by short
wavelength (386 nm) light gave green light as emission.
As there is no green light excitation for the 386 nm we
can come to a controversial question: is the green colour
that our eyes see on plants mostly an emission or a re-
flection? If it is an emission, it is contrary to what we
learn in schools and specialized literature [1-3,13,15].
Note that these experiments were performed in vivo and
not on chemicals separated from leaves. The conversion
mechanism from ultra-violet, violet and blue excitation
to green, yellow and red emission is postulated as pri-
marily due to type II energetic interfaces. This proposi-
tion does not imply that there is no green (and others
colours) reflection, transmission and diffusion (scattering)
when leaves are excited with sunlight. Also, it cannot be
ruled out the possibility of green absorption and red shift
green emission by the many possibilities of existing type
II interface within a leaf (see igure SI-4-4). This means F
Copyright © 2012 SciRes. WJNSE
Copyright © 2012 SciRes. WJNSE
yellow part
of the leaf
green part
of the leaf
532 nm
ilter 300K
Figure SI-4-2. Room temperature photoluminescence spectra of yellow-green intact Erytrina indica picta leaves, excited with
532 nm wavelength, 10 ns pulses from a Nd: YAG laser. To avoid the 532 nm laser line, a 532 - 560 nm filter is placed be-
tween the leaf and the spectrometer. Orange spectrum is from the yellow part of the leaf. Green colour spectrum is from the
green part of the leaf. No correction is proposed for the intensity axe. No smoothing was performed for both curves. These
two spectra suggest that the emission spectrum of different regions (colours) in a leaf depends also on the excitation wave-
lengths. This result shows clearly that leaves’ internal machinery is able to absorb more energetic photons and emit less en-
ergetic photons. Both curves show that there is absorption of green light, an internal transformation and emission at longer
wavelength (lower energy) by the leaves.
excitation wavelen
386 nm
yellow part of the leaf
reen part
of the leaf
T = 300K
Figure SI-4-3. Room temperature photoluminescence spectra of yellow-green intact Erytrina indica picta leaves, excited with
386 nm wavelength, 10 ns pulses from a Nd:YAG laser. To avoid the 386 nm laser line, a cut-off filter below 450 nm is placed
between the leaf and the spectrometer. Orange spectrum is from the yellow part of the leaf. Green colour spectrum is from
the green part of the leaf. No correction is proposed for the intensity axe. No smoothing was performed for both curves. Note
that the yellow part of the leaf has much higher green colour intensity than the green part of the leaf. Also, the green part of
the leaf presents a much higher red intensity than the yellow part of the leaf. These two spectra suggest that the emission
spectra of different regions (colours) in a leaf depend also on the excitation wavelength. This result shows clearly that leaves’
internal machinery is able to absorb more energetic photons and emit less energetic photons. The observed green intensity is
an emission and not a reflection, since there is no excitation with green colour. Note that the leaf is absorbing non-green pho-
tons and emitting green photons. It means that the green colour of plants is not only composed by green colour reflection.
4.42 eV
3.35 eV
2.0 eV
Cr Chl-b
2.25 eV
2.95 eV
2.75 eV
2.48 eV
3.02 eV
2.81 eV
1.83 eV
2.75 eV
2.58 eV
2.06 eV
1.92 eV
4.42 eV
3.81 eV
3.31 eV
2.81 eV
Figure SI-4-4. The Mother Nature puzzle. Representation (on vertical strips) of energy band gap for the leaves’ constituent,
containing 3 - 4 mains absorption peaks depicted within each strip. Each coloured rectangle with eV energy represents en-
ergy peaks absorption for the molecules. These energy bands absorption were taken from the literature [13,15]. They repre-
sent possible band gap energies within each individual molecule (separated from leaves). The authors do not know the energy
bandgap relative positions for the chromophores in leaves. This means that electrical charges travelling on the leaves’ mole-
cules energetic bands should see energetic steps (up or down) that are not known. As the ground state energy energetic rep-
resentation does not represents any natural and physical entity, to much work is needed to find out these energetic steps for
in vivo leaves. The energy bands absorption for the cell, protoplast and chloroplast environment are not known by the au-
thors. From one of these band gaps energy relative positions, a staggered one can emerge the main green colour of leaves we
have today, for each excitation photon. From others energy relative positions emerge the others less intense colours as yellow,
brown, red, from leaves. Genetically leaves can use them on machinery for adaptation/evolution and have different colours as
emissions. Note also that these energy absorption values were taken from chemical separated from the leaves. For leaves “in
vivo”, it should change these values because the emission and absorption properties are also interface related. Note that these
strips configuration is only one in between many others possibilities to have type II (staggered), type I and type III energetic
interfaces (see text). The arrows indicate possible staggered energy band gap relative position and (e, h+) recombina-
tion/transitions. This figure shows that, even for a non in vivo situation, it is impossible not to have a staggered band gap en-
ergy configuration between two or more molecules. The size of molecules and distances in between molecules within a leaf is
about 1 nm. As discussed within the text, the electrical charges wavefunction penetration is much higher that 1 nm. The in-
volved attraction/recombination/emission mechanism cannot be considered as a non quantum mechanics one. The staggered
energy configuration gives us the physical situation to have a quantum mechanism for photosynthesis. As (e–, h+) are seated
on different materials, quantum k selections rules do not hold anymore for these recombination/transitions/ emissions when
considering type II energetic interface. eV represents the electron volts energy from the absorption energy peaks, extracted
rom the literature. Cr = carotene, Chl = chlorophyll.
Copyright © 2012 SciRes. WJNSE
Copyright © 2012 SciRes. WJNSE
interface absorption, as discussed in the main text.
Blue-green laser induced fluorescence from intact
leaves has been observed by many research groups, using
UV (308 nm) excitation, as M. Broglia and E. Chapelle
et al. [39,40]. There is no conclusion presented by these
authors, for the observed green fluorescence. Their re-
sults show also that the blue-green-red fluorescence can
be ascribed to others structures, such as cell envelopes
and vacuolar solutes [39,40]. This indicates that the en-
vironment of the constituents of the leaves play an im-
portant role in colour emission from leaves. Nanosecond
decay of chlorophyll fluorescence from leaves has been
attributed to the recombination of separated charges in
the reaction centre of PSII [30]. The environment of the
leaves’ constituents and the recombination of separated
charges, both support our proposition for green light
emission as being mostly a type II interface mechanism
(see text).
Figures SI-4-2 and 3 show that leaves’ constituents,
composed of organic materials, are able, with their inter-
nal machinery to transform absorbed photons on to emit-
ted photons of lower energy. We propose that many of
these mechanisms can be associated to type II interface
emission. Some of them can be associated to absorption
and emission at nearly the same wavelength (interface
As most of the leaves contain many kinds of mole-
cules having 3 - 5 absorption peaks, when separated from
the matrix, it is reasonable to expect many possible den-
sity of states energy band overlap from these absorption
bands when they are not separated from the leaf (using
intact leaves).
On Figure SI-4-4 we present one of these type II in-
terfaces possibilities for many chemicals green leaves
constituents. This figure shows that it is impossible not
to have type II interface energetic configuration between
the leaves’ constituents.
Comparing Staggered Energy Band Gaps and
the Presently Accepted Ground State Energy
The currently accepted model for the photosynthesis me-
chanism is based roughly on absorption of visible sunli-
ght in the red and blue regions of the spectra, with no
absorption (and consequently a conclusion to the exis-
tence of a reflection and/or scattering mechanism) in the
green spectral region [1-3,13,39-42]. The currently ac-
cepted model for photosynthesis is based on classical
physics and uses the ground state energy (GSE) configu-
ration to explain the light absorption by certain mole-
cules and its energy transfer to others molecules (FRET).
As indicated within the text, the accepted model suffers
from few problems concerning the charges separation and
violations of physical laws.
Contrary to usual believes, the absorption of photons
is not enough to have electrical charges separated [1,13,
80]. The absorption of photons gives rise to an excited
state between e– and h+, called exciton. To break up this
excitonic energetic configuration we need a physical
energetic configuration to allow a driving force to per-
form this work. This driving force should come from a
varying potential (the origin of the electric field). With-
out an appropriate electric field and without spending
energy to separate e– from h+ any other model violates
physical laws.
The present proposed model for photosynthesis, based
on type II energetic interfaces, is based on the sun visible
light spectra absorption by the Nature’s green leaves
constituent. These materials can be chlorophylls, carote-
noids, phycoerythrin, phycocyanin, protoplast, water, etc
and the physical structure within a chloroplast. The type
II energetic configuration and its application to explain
electrical charges separation possess all the physical
tools (energetic configuration, electric field and spent
energy) to separate e– from h+.
The green (or yellow or red) colours of Nature’s leaves
depend on the (e–, h+) wavefunction overlap or tunnelling
process. It is a very fast process (compared with usual
CB-VB semiconductor recombination mecha- nism) and
its efficiency comes from the non existing quantum me-
chanics selection rules, even if it is a quantum mechanics
assisted mechanism as proposed within the main text.
Recently many papers based on very sophisticated and
beautiful optical experiments got to the proposition that
photosynthesis is a quantum mechanical mechanism, but
without presenting it [64-71]. The present staggered, type
II interface, band gap energy proposal supports this quan-
tum mechanical dynamic mechanism. Based on theoretical
calculations, De Angelis et al. got to the conclusion for a
staggered energy representation between two organic
molecules, the same concept holds for inorganic/ organic
materials [11,47-60]. That is exactly what we are pro-
posing: (e–, h+) charges have energetic steps when trav-
elling from a material to another. This physical energetic
steps concept cannot be put beside and it is the basis for
when working and considering different materials. In
another way, electric charges have always energetic steps
when moving from a material to another. On the contrary,
the ground state energy representation (or a band gap
engineering, old of tens of years) is an unrealistic and a
non-existing physical interface energetic representation
[1-5,7-13]. The ground state energy does not allow a
quantum mechanics mechanism development for the
photosynthesis first step explanation [4-10]. There is no
proof of and for the “ground state energy” (GSE) repre-
sentation. Charges do not care about GSE representation.
Charges care about energetic steps within the molecules
or in between the molecules (or materials). GSE repre-
sentation does not allow the apparition of an electric field
for both (e–, h+) charges separation. GSE representation
does not allow the apparition of the spent energy to
separate electrical charges under attraction. In this sense,
the GSE representation violates physical laws in trying to
explain the charges separation mechanism; the photo-
synthesis first step process. Leaves have their internal
machinery, able to absorb photons and emit light at
lower energy, to waste quickly (emission) most of the
visible sunlight radiation. The 79% absorption (see text)
of visible light by leaves should follow the staggered
energetic representation to get rid of most of the ab-
sorbed visible (400 - 700 nm) light [13-72].
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