Materials Sciences and Applications, 2010, 1, 210-216
doi:10.4236/msa.2010.14033 Published Online October 2010 (
Copyright © 2010 SciRes. MSA
Effect of Mn Doping on Solvothermal Synthesis of
CdS Nanowires
Zinki Jindal1,2, Narendra Kumar Verma1
1School of Physics & Materials Science, Thapar University, Patiala, India; 2Department of Physics, Sir Padampat Singhania University,
Udaipur, India.
Received May 20th, 2010; revised July 26th, 2010; accepted September 27th, 2010.
High aspect ratio (up to 100) CdS nanowires having average diameter of 15 nm and length varying from 0.5-1.5 μm
have been synthesized using solvothermal technique in ethylenediamine as a solvent at 120 and the effect of Mn dop-
ing on morphology and optical properties has been studied. X-ray diffraction analysis shows the typical inter-planar
spacing and the diffraction peaks corresponding to the hexagonal wurzite phase of CdS. Morphological study has been
done through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and the optical studies
have been conducted through absorption spectra and room temperature photoluminescence (PL).
Keywords: Nanomaterials, Semiconducting Cadmium Compounds, Growth from Solutions, Nanostructures, Nucleation
1. Introduction
One dimensional (1D) nanostructures are considered to
be critical building blocks for nanoscale electronic and
optoelectronic devices and have received tremendous
attention since the discovery of carbon nanotubes [1-9].
CdS is one of the most studied materials due to its exten-
sive applications in photoelectric conversion in solar
cells and light-emitting diodes in flat panel displays [10].
CdS nanowires have been synthesized by several tech-
niques. For instance, the growth of thin CdS nanowires
(20 nm thick) has been achieved by a laser ablation
technique or chemical vapor deposition (CVD) process
based on a gold nanocluster catalyzed vapor-liquid-solid
(VLS) growth mechanism [11]. CdS nanowires with di-
ameters of 30-70 nm have also been synthesized simply
by thermal evaporation of CdS powders [12]. Neverthe-
less, the above mentioned methods need some special
instruments, harsh conditions, and/or relatively high per-
formance temperature (over 800). Uniform nanowires
of CdS could also be obtained in the channels of various
templates, such as anodic aluminum oxide (AAO) mem-
brane [13], polymer gels [14], micelles [15], and so on
[16]. Although the template-directed methods are effect-
tive in preparing nanowires with uniform and controlla-
ble dimensions, they usually lead to a complicated proc-
ess and also impurities due to the incomplete removal of
the templates, and the yields are relatively low. Moreover,
high aspect ratio (length to diameter) CdS nanowires
have also been prepared by solvothermal process [9,
17-19], which may provide a more promising technique
for preparing CdS nanowires than conventional methods
in terms of cost and potential for large-scale production.
The modification in the properties of the semiconducting
nanomaterials can be done by tailoring their energy band
structure [20,21] with ion implantation, ion doping,
chemical vapor ion doping [22]. Nanomaterials doped
with optically active luminescence centers create new
opportunities for luminescence research and also for the
application of nanometer-scale structured materials.
Many research groups have studied the optical, magnetic
and fluorescent properties of Mn-doped CdS nanocrys-
tals [23-26]. But most studies focus on doped CdS
nanoparticles. However, there is a need of studying the
changes in the properties of the 1D nanoforms (undoped
as well as doped) for their potential application in nano-
scale optoelectronic devices.
This paper describes the successful synthesis of high
aspect ratio of CdS nanowires by the solvothermal tech-
nique, using ethylenediamine (En). The effect of Mn
doping on the growth of the nanowires and the optical
properties have also been discussed. Optical properties of
the doped nanoforms indicate that the dopant incorpora-
tion in the host plays an active part in controlling the
Effect of Mn Doping on Solvothermal Synthesis of CdS Nanowires
Copyright © 2010 SciRes. MSA
luminescence properties.
2. Experimental
The synthesis of CdS nanowires has been carried out in a
closed cylindrical teflon-lined stainless steel chamber.
All of the chemical reagents used in this experiment were
of analytical grade and used without further purification.
Cadmium foils were used as a substrate and also as an
additional source of cadmium. 0.005 M cadmium nitrate
[Cd(NO3)2.4H2O] along with 0.015 M thiourea [CSN2H4]
were taken with 70ml of ethylenediamine (En) which
acted as the solvent in the teflon chamber (capacity ~100
ml). Mn doped CdS nanostructures were also prepared by
adding 5 mmol and 10 mmol manganese acetate (Mn
(CH3COO)2). The properly sealed teflon-lined stainless
chamber was maintained at temperature of 120 for 24
hours in an electric oven and afterwards, it was allowed
to normally cool down to room temperature. The foil and
the yellow colored precipitates were collected from the
reaction vessel and were washed with de-ionized water
and ethanol several times and subsequently dried in air at
50 for 6-12 hours.
The products were characterized by Panalytical’s
X’Perto Pro X-ray diffraction machine using the copper
characteristic wavelength of 1.5418 Å. Microstructures
of the nanoforms were studied through scanning electron
microscopy (SEM, FEI, Nova 200 NanoLab) and trans-
mission electron microscopy (TEM, Hitachi, H-7500).
Optical absorption spectra of the products, dispersed in
spectroscopic grade ethanol, were recorded by a Hitachi
330 UV-Vis spectrophotometer. Photoluminescence (PL)
measurements were carried out at room temperature with
a luminescence spectrometer (Varian Cary Eclipse fluo-
rescence spectrophotometer) using 336 nm as the excita-
tion wavelength.
3. Results and Discussion
Figure 1 shows the XRD pattern of the synthesized CdS
nanowires with all the diffraction peaks corresponding to
the hexagonal wurzite phase of CdS. These match well
with those in the JCPDS Card (Joint Committee on Powder
Diffraction Standards, Card no. 41-1049), as shown in
Figure 1. No impurity peaks were detected, indicating
high purity product. In addition, the intense and sharp
diffraction peaks suggest that the obtained product is
well crystallized. The d-spacing of the CdS nanowires
have been calculated using the XRD analysis and com-
pared with the standard JCPDS data (Table 1). The cor-
responding (hkl) values are illustrated in the table.
In case of solvothermal synthesis, temperature and
concentration plays an important role in the formation of
crystal structure, shape and size of the nanoforms. The
20 30 40 50 60 70
Intensity (arb. units)
20 30 40 50 60 70
JCPDS card 41-1049
Figure 1. XRD pattern of the CdS nanowires revealing their
hexagonal wurzite phase, and the standard JCPDS card No.
Table 1. The comparison of d-values, obtained from XRD
and JCPDS, and illustration of the corresponding (hkl) val-
Peak 2θo d
XRD(Å) dJCPDS(Å) (hkl)
1. 25.04 3.5561 3.5861 100
2. 26.78 3.3289 3.3599 002
3. 28.52 3.1296 3.1630 101
4. 37.07 2.4251 2.4519 102
5. 43.88 2.0632 2.0705 110
6. 48.08 1.8924 1.8998 103
7. 52.09 1.7557 1.7627 112
mechanism behind the formation of nanorods, in pres-
ence of ethylenediamine (En) as chelating agent, has al-
ready been discussed by many researchers [18]. En reacts
with the Cd2+ ions to form Cd-En complex lamellar
products, which react with the S2- ions to produce CdS-En
lamellar materials. The high temperature leads to the
breakage of volatile amine groups giving rise to lamel-
lar-to-rod transitions. This is known to proceed via the
rolling mechanism [27].
The morphology and the dimensions of the nanowires
were studied through scanning electron microscopy
(SEM) and transmission electron microscopy (TEM).
Figures 2(a, b), 2(c) and 2(d) show the SEM images of
undoped, 5 mmol and 10 mmol Mn doped CdS nanos-
tructures, respectively. Figures 2(a, b) show the growth
of highly dense CdS nanowires having diameters varying
between 9-40 nm and lengths varying from 0.5 to 2 μm.
The ends of the nanowires are still attached to adjacent
nanoforms, possibly due to the incomplete transforma-
tion of the lamellae to the nanowires. Whereas, on dop-
Effect of Mn Doping on Solvothermal Synthesis of CdS Nanowires
Copyright © 2010 SciRes. MSA
(a) (b)
(c) (d)
Figure 2. SEM images of (a, b) undoped and (c) 5 mmol (d) 10 mmol Mn doped CdS nanostructures.
ing with Mn, and on increasing the concentration of Mn
from 5 to 10 mmol (as per the experiment performed), it
has been observed that this lamellar-to-rod transition has
decreased. Figure 2(c) shows the fragmentation of these
Mn doped CdS-En (5 mmol Mn) lamellae to higher level
as compared with those of Figure 2(d) (10 mmol Mn),
where this fragmentation is still in the initial stage. The
reason behind this inhibition of CdS nanowire growth on
addition of Mn dopant is not clear at this moment. The
Mn dopant is considered to bind to the most stable sur-
face sites formed during the nanowire nucleation, which
inhibits the advancement of the growth in the particular
direction [28].
Figures 3(a, b, c, d) show the formation of high aspect
ratio (up to 100) CdS nanowires. The diameter of the
synthesized nanowires ranges from 9 to 18 nm, whereas
the length varies from 0.5 to 1.5 μm. Figures 3(a, b)
shows the bundles of the CdS nanowires where the indi-
vidual nanowires can be well distinguished, whereas
Figures 3(c, d) shows the individual nanowires. More-
over, the flexibility of the CdS nanowires can be ob-
served from Figures 3(c, d), by their wavy nature.
Figure 4 shows the optical absorption spectra of the as
synthesized undoped and Mn-doped (5 mmol Mn) CdS
nanowires. The maximum absorption peak positions of
CdS and CdS: Mn nanoforms are at 460 and 469 nm re-
Effect of Mn Doping on Solvothermal Synthesis of CdS Nanowires
Copyright © 2010 SciRes. MSA
(a) (b)
(c) (d)
Figure 3. (a-d) TEM images of undoped CdS nanowires.
spectively, as compared with that of CdS bulk materials
(515 nm). The band gap energies were calculated from
the differential minima, which varied from 2.48 eV to
2.44 eV on doping with Mn. The observed diameters of
the CdS nanowires are well above its Bohr`s exciton ra-
dius (2.8 nm), therefore, this shift in the band gap ener-
gies may not be related with quantum confinement effect.
The small change in the band gap values may be attrib-
uted to the direct energy transfer between the semicon-
ductor excited states and the 3d levels of the Mn2+ ions,
that are coupled by energy transfer processes [29].
The room temperature photoluminescence (PL) meas-
urement results of the CdS nanowires (undoped and
doped with Mn) are shown in Figure 5. The excited
wavelength was 336 nm, and no filter was used. In the
past several decades, the luminescence mechanisms of
CdS have been studied. Usually, two emissions are ob-
served from the semiconductor nanoparticles – excitonic
and trapped luminescence [30]. The excitonic emission is
sharp and located near the absorption edge of the particles,
Effect of Mn Doping on Solvothermal Synthesis of CdS Nanowires
Copyright © 2010 SciRes. MSA
400500600700400 450 500 550 600 650 700
CdS pure
469 nm
460 nm
Absorbance (arb. units)
Wavelength (nm)
Figure 4. Optical absorbance of the as synthesized CdS,
undoped and doped with Mn (5 mmol), nanowires.
460 480 500 520 540 560580 600 620 640500600500600
481 nm
599 nm
595 nm
555 nm
517 nm
Intensity (arb. units)
Wavelength (nm)
Figure 5. Room temperature PL spectra of (i) undoped CdS
and (ii) 5 mmol (iii) 10 mmol Mn doped CdS nanowires (λex
~ 336 nm).
while the trapped emission is broad and stokes-shifted.
CdS is a wide-band-gap (Eg = 2.42 eV) semiconductor
and has typically two emission bands: green band (exci-
tonic emission) around 518 nm and the red band (as-
cribed to trap of surface states) at about 732 nm [31]. But
due to their 1D geometrical characteristic at the nanome-
ter scale, CdS nanowires are expected to have different
physical properties from their bulk counterparts [32].
Moreover, it is also believed that nanowires with high
aspect ratio have more surface and subsurface defects
such as grain boundaries and sulfur/cadmium related
defects. These would definitely exert an influence on the
PL properties of the CdS nanowires. Room temperature
PL spectra of undoped CdS nanowires exhibit a weak
and sharp emission at 481 nm and a broad green emis-
sion band centered at 517 nm. The weak emission band
at shorter wavelengths is attributed to the direct transition
from the conduction to the valence band [33]. This indi-
cates that the particle crystallinity is rather high. The
main luminescence band is broad and is attributed to CdS
trap emission. The electrons and holes, after excitation
across the band edge, trickle down non-radiatively to the
surface states lying in the bandgap region. Radiative
de-excitation across the surface states in CdS nanowires
gives rise to green fluorescence observed at around 517
nm. On addition of Mn (5 mmol) dopant, the intensity of
the direct transition has been found to decrease and the
broad band, red shifted to 595 nm, which is similar to the
Mn emission in bulk CdS:Mn due to an internal Mn2+
transition (4T16A1). On increase in the concentration of
Mn (5 to 10 mmol), this broad band has red shifted to ~
599 nm, indicating that the Mn2+ concentration is suffi-
cient to influence the crystal-field splitting between 4T1
and 6A1 states [34]. Moreover, a broad band, centered
around 555 nm, has evolved on the increase of Mn con-
centration, which may be attributed to the deep surface
trap recombination, unlike from defect related states [35].
4. Conclusions
In summary, we have studied the effect of Mn doping on
the solvothermal synthesis of CdS nanowires. The mor-
phological study showed that the lamellar-to-rod transi-
tion of CdS has decreased on increase in concentration of
Mn dopant, while keeping all the other reaction condi-
tions same, like: temperature, time duration, solvent,
concentration of Cd and S precursors. This might be due
to the binding of Mn to the most stable sites during the
nanowires nucleation, leading to the inhibition of the
growth in a particular direction. CdS nanowires exhibit
broad green emission and on addition of Mn, 5 mmol,
this band has red shifted to characteristic 595 nm. On
further increase of Mn concentration to 10 mmol, there is
additional red shift of 4 nm of this broad band. And an-
other emission centered around 555 nm has been ob-
served, possibly due to deep surface trap recombination.
In future, due to the potential applications of CdS: Mn
nanowires in the field of optoelectronics, there is need of
more detailed study regarding the mechanism.
5. Acknowledgements
We acknowledge Defence Research & Development
Organisation (DRDO), Government of India, for their
generous funding for the research work vide their letter
No. ERIP/ER/0504321/M/01/855 dated 16th December
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