World Journal of Nano Science and Engineering, 2012, 2, 13-18
http://dx.doi.org/10.4236/wjnse.2012.21003 Published Online March 2012 (http://www.SciRP.org/journal/wjnse) 13
Synthesis and Characterization of Eu+++ Doped Y2O3 (Red
Phosphor) and Tb+++ Doped Y2O3 (Green Phosphor) by
Hydrothermal Processes
Ravindra P. Singh1, Kiran Gupta2, Ashutosh Pandey2, Anjana Pandey1*
1Nanotechnology and Molecular Biology Laboratory, Centre of Biotechnology, University of Allahabad, Allahabad, India
2Department of Chemistry, Motilal Nehru National Institute of Technology, Allahabad, India
Received June 16, 2011; revised July 22, 2011; accepted September 10, 2011
ABSTRACT
Eu+++ and Tb+++ doped Y2O3 nanoparticles have been synthesized by hydrothermal process using yttrium oxo-isopro-
poxide Y5O(OPri)13 as precursor (OPri = isopropxy). X-ray diffraction (XRD), transmission electron microscopy (TEM),
nanoparticle size analyzer and photoluminescence (PL) spectroscopy have been used to characterize these powders. The
as synthesized powders gave very sh arp peak in the X-ray diffraction suggesting crystalline particles with average par-
ticle size between 28 - 51 nm for Eu+++ doped Y2O3 nanoparticles and 43 - 51 nm for Tb+++ doped Y2O3 nanoparticles
annealed at 300˚C for 3 h, 4 h and 5 h, which could be unique in comparison to other reports. Transmission electron
micrograph investigation of the particles shows single dispersed particles along with agglomerates. The ratio of intensi-
ties of transitions in the europium and terbium emission spectrum have been used as structural probe to indicate the lo-
cal environment around Eu+++ and Tb+++ in the Y2O3 particles.
Keywords: Yttrium Oxo-Isopropoxide; Nanophosphors; Y2O3:Eu+++; Y2O3:Tb+++; Hydrothermal Process
1. Introduction
The research of efficient and inexpensive nanoparticles is
a challenging problem for the new materials generation
[1]. The production of luminescent materials for tech-
nology applications requires strict control over their pow-
der characteristics which include chemical homogeneity,
low impurity levels and a sub micrometer particle size
with a narrow distribution [2,3]. The conventional phos-
phor production through high temperature solid state
reactions typically results in particle sizes of 5 - 20 nm
[4]. Aiming at nanometer sized oxide particles, more
advanced types of synthesis are then required [5,6]. Since
the yttrium oxide presents good luminescent properties
when doped with rare earth ions (Eu+++, Tb+++) [7-9], the
oxide phosphor materials could be a good example to
improve the luminescence properties and to extend the
application field to a large domain [10,11].
Rare earth ions doped nanocrystalline metal o xides are
a class of luminescent materials (also called u pconverting
phosphors) which have been proved to be excellent for
applications such as in field emission displays (FEDs),
cathode ray tubes (CRTs) and plasma display panels
(PDPs), optoelectronic devices, biological fluorescence
labelling, luminescent paints and inks for security codes
and many more [12]. Under UV irradiation Eu+++ doped
Y2O3 is a red phosphor and Tb+++ doped Y2O3 is a green
phosphor. It is possible that, due to their high quantum
efficiency, they might serve as improved luminescent
markers for identification of biomolecules, as already re-
ported for CdSe and CdSe/ZnS nanocrystal [13]. However,
for any biological applications these particle powders must
be suspended in water while retaining their phosphores-
cence. Over the years a number of different routes, such
as spray drying, freeze-drying, sol-gel, co-precipitation,
self-sustaining combustion, emulsion technique, hydro-
thermal method, template method, electrochemical method
or combinations thereof have been used to synthesize
RE-doped Y2O3 nanophosphors [14-21]. We hereby repo r t
synthesis & characterization of Eu+++ and Tb+++ doped
yttrium oxide nanoparticles by hydrothermal processes
and compare its characteristics with the other reported
methods for these nanoparticles. Eu+++ and Tb+++ doped
Y2O3 nanoparticles have been synthesized by hydrothermal
technique using yttrium oxo isopropoxide [Y5O(OPri)13]
as precursor.
Generally the metal oxides derived by sol-gel method
are required to be annealed to temperature ranging from
400˚C - 800˚C in order to develop crystalline phases [22].
*Corresponding author.
C
opyright © 2012 SciRes. WJNSE

R. P. SINGH ET AL.
14
However, this annealing also results in development of
aggregates which are undesirable for bio-conjugation ex-
periments. But in ou r case th e crysta llin ity wa s ach ieved at
300˚C by hydrothermal process. The average particle
sizes as calculated from XRD were found between 28 nm
to 51 nm in case of Eu+++ doped Y2O3 and 43 nm to 50
nm in case of Tb+++ doped Y2O3 nanoparticles at 300˚C
for 3 h, 4 h and 5 h. The TEM investigations showed the
presence of single particles along with agglomerates.
2. Experimental
2.1. Synthesis and Characterization of
(Y5O(OPri)13 Precursor
The precursor Y5O(OPri)13 was synthesized and charac-
terized by the method of Ashutosh Pandey et al. [22].
Y5O (OPri)13 was used as precursor in hydrothermal pro-
cess for making yttrium oxide nanoparticles. The manipu-
lation pertaining to synthesis of Y5O(OPri)13 precursor
was performed under dr y argon atmosphere using Schlen ck
techniques. The solvent were dried and purified by stan-
dard procedures. Water was doubly distilled, deionized
and purified by standard procedures. Yttrium chips (Al-
drich), toluene, isopropanol, Hg(OAc)2 (all qualigens)
were used to perform the chemical reaction which gave
the precursor in 70% yield. It was characterized by ele-
mental analysis (Found (%) C 38.15, H 7.70: calculated
C 38.12, H 7.12) and NMR spectroscopy {1H NMR in
ppm}, 1.29 (doublet), 4.30 (septet) in dry CDCl3 and
found in accordance with reported values.
2.2. Synthesis of Eu+++ and Tb+++ Doped
Nanoparticles by Hydrothermal Method
83 ml of 0.1 M HNO3 was added dropwise to Y5O(OPri)13
(13.0 g) with vigorous stirring. At the same time a mix-
ture of 4.51 g Eu(NO3)3·5H2O (for 0.2 M doping) and
0.945 g water was added dropwise to it under stirring.
After the addition was completed, white precipitate form-
ed instantaneously. The slurry was refluxed and stirred
vigorously for 8 h, to achieve peptization. The colloidal
solution was introduced in a rotary evaporator and eva-
porated (50˚C, 30 mbar) to get desired volume of sus-
pension. The growth of these particles was achieved un-
der hydrothermal condition and sedimentation occurred
during the hydrothermal condition. After the decantation
of above milky liquid portion, we got colloidal suspen-
sion of europium doped yttrium nanoparticles. The col-
loidal susp ension was dried in oven at 10 0 ˚C to achiev e a
white powder. It was subjected to heat treatment at
300˚C for 3 h, 4 h and 5 h respectively. Upon heating to
different time, the Eu+++ doped (0.2 M doped) material
did not show any discernable change in white color of
the starting powder.
A similar procedure was applied for Tb+++ doped
powders for which 4.51 g Tb(NO3)3·5H2O was used for
0.2 M doping. The resulting suspension was dried in an
oven at 100˚C to give white powder. It was subjected to
heat treatment at 300˚C for 3 h, 4 h an d 5 h respectively.
Tb+++ doped Y2O3 powder did not undergo any colour
change upon heat treatment to different time.
2.3. Characterization
The proton and C13 NMR spectra were recorded by
GEOL-300 MHz spectrometer at BHU Varanasi, X-ray
diffraction pattern were recorded on Seifert powder dif-
fractometer using Cu-Kα X-rays. The surface morphol-
ogy of samples was studied by the transmission electron
microscopy on model Tecnai G20-twin. The secondary
particle size of TiO2 nanoparticles were measured by
Nanotrac particle size analyser. The photoluminescence
spectra were recorded on an ocean optics system with
range 200 - 1800 nm using an excitation wavelength of
440 nm.
3. Results and Discussion
Europium (Eu+++) and terbium (Tb+++) doped Y2O3 is a
well-known and efficient red emitting luminescent mate-
rial finding extensiv e application in displays, in vivo bio-
logical imaging and as a luminescent security ink for
detecting any counterfeiting, alteration and unauthorized
trading [23]. It is an insulator with a bulk band gap of 5.6
eV and hence strongly absorbs at energies with wave-
lengths of less t han 2 30 nm .
In the presen t investigation, we have successfully syn-
thesized a Eu+++ and Tb+++ doped Y2O3 nanophosphors of
average size 28 - 51 nm using hydrothermal technique and
finally developed highly transparent and nonaqueous-
stable nanophosphor s for bio-conju g ation app licatio ns . In
order to understand the stability of colloids, which has a
direct relation to particle size, we carefully monitored the
morphology of selective experiments. Slow and con-
trolled heat treatments to the nanoparticles were per-
formed to tailor the Y2O3:Eu+++ and Y2O3:Tb+++ nano-
phosphors for enhanced brightness level. Europium and
terbium doped (0.2 M concentration) Y2O3 white powder,
were derived by hydrothermal methods and warmed to
100˚C.
The obtained nanoparticles were annealed to 300˚C for
3 h. X-ray diffraction patterns for the Eu+++/Y2O3 doped
particles are shown in Figure 1. All peaks in Figure 1(a)
correspond to that cubic structure of Y2O3, indicating that
crystallinity was achieved at 300˚C. However, the sol-
vent molecules were completely expelled after annealing
at 400˚C to achieve the crystallinity [22 ]. So the obtained
nanoparticles were further heated to 4 h and 5 h at the
same temperature i.e. 300˚C to observe the effect of fur-
ther annealing on the particle size of these nanoparticles.
These show that our samples achieved crystallinity at

R. P. SINGH ET AL. 15
300˚C when annealed for 3 h in hydrothermal process
which differentiates these nanoparticles from several tech-
niques, such as sol-gel technique [22] and alkalide reduc-
tion method [24]. The crystallinity was achieved at 500˚C
and above in case of alkalid e redu ction and 400˚C in case
of sol-gel technique. The peak positions of the entire
specimen showed (222) p eak with high est in tensity in the
XRD patterns. The diffraction peak in the patterns is in-
dexed to cubic equilibrium structure for Eu+++/Y2O3 and
Tb+++/Y2O3 nanoparticles. The average particle size (d)
was calculated using the Scherer’s formula.
(a)
(b)
(c)
Figure 1. XRD pattern of 0.2 M Eu+++ doped Y2O3 nano-
particles synthesis zed by hydrothermal method annealed at
300˚C for 3 h, 4 h and 5 h (a-c).

d0.9 B cosλθ
The average particles sizes with respect to sharp peaks
are 28, 32, 34 nm in case of Eu+++/Y2O3 nanoparticles
and 43, 46, 50 nm in case of Tb+++/Y2O3 nanoparticles
respectively at 300˚C for 3 h, 4 h and 5 h.
The morphological aspect of the resulting powders
synthesized by hydrothermal technique was examined by
TEM, as shown in Figure 2. The micrographs revealed
the formation of agglomerates, along with single dis-
persed particles. An X-ray diffraction indicated that all of
these agglomerates consisted of Y2O3 doped with Eu+++/
Tb+++ ions.
Figure 3 shows the particle size distribution corre-
sponding to sample Eu+++/Tb +++ doped Y2O3 nanoparti-
cles soluble in chloroform. The graph shows the uniform
(a) (b)
Figure 2. TEM images of (a) 0.2 M Eu+++ (b) 0.2 M Tb+++
doped Y2O3 synthesi zed by hydrothermal process.
(a)
(b)
Figure 3. Particle size distribution coresponding to samples
[1] 0.2 M Eu+++/Y2O3 and [2] 0.2 M Tb+++/Y2O3 nanoparti-
cles soluble in chloroform.

R. P. SINGH ET AL.
16
stability and improved homogenicity of nanoparticles in
case of Eu+++ doped Y2O3 suitable for bioconjugation.
The particle size analysis showed that these are nonag-
gregated and spherical in shape. But in case of Tb+++
doped Y2O3 nanoparticles, a group of nanoparticles are
present with various sizes because of agglomeration of
nanoparticles. The average secondary particle sizes calcu-
lated by nanotrac particle size analyzer were 110 nm and
140 nm for Eu+++ Tb+++ doped Y2O3 nanoparticles.
The distribution of the Eu+++ ions within the host Y2O3
matrix has been worked out by examination of the pho-
toluminescence spectra, which is shown in Figure 4 for
both the 0.2 M Eu+++:1 M Y2O3 (a) and 0.2 M Tb+++:1 M
Y2O3 (b).
PL spectra of all the samples were recorded using an
excitation wavelength of 440 nm. The most characteristic
peaks at 592 nm, 612 nm and 675 nm, which correspond
to 5D0→7F1, 5D0→7F2 and 5D0→7F4 transitions in case of
europium while in case of terbium the most characteristic
peaks at 486, 481, 470, 456, 436, 414, and 381 nm, which
correspond to 5D3→7F0, 5D3→7F1, 5D3→7F2, 5D3→7F3,
5D3→7F4, 5D3→7F5 and 5D3→7F6 transitions have been
reported [25].
In our study, the photoluminescence spectrum for the
nanoparticles synthesized and annealed at 300˚C for 3 h
bears a completely different look which is similar to
powder synthesized by sol-gel method and annealed at
Figure 4. Photoluminescence spectra of Eu+++ (0.2 M) and
Tb+++ (0.2 M) doped Y2O3 prepared by hydrothermal me-
thod, annealed at 300˚C for 3 h.
800˚C [22]. In general, the sharp emission lines point
towards occupation of Eu+++ ions in these crystallogra-
phic site that are situated in the interior of the nanocrystal.
In particular, the 0.2 M Eu+++ samples show slightly
broadened peak in the corresponding region indicating
that in them some of the Eu+++ ions might have gone to
particle boundaries. It may be due to sudden onset of
thermodynamic process which extracts europium from
the symmetrical octahedral sites in Y2O3 lattice and
places them at the particle boundary and show simulta-
neous emission from site with different crystal field split-
ting. The powder which was annealed at 300˚C for 3 h,
showed the prese nce of 5D0→7F1, 5D0→7F2 as well as the
5D0→7F4 transition lines, each with a larg e broadening so
that they have merged together confirming the presence
of europium ions in unsymmetrical environments (Table
1).
Similarly PL spectrum for 0.2 M doping concentration
of Tb+++ within the Y2O3 matrix is showed in Figure 4.
The Tb+++/Y2O3 nanoparticles showed following transi-
tions i.e. 5D3→7F1, 5D3→7F2 and 5D3→7F3 which over-
lapped together. All of these peaks have a very large
broadening so that they merged together confirming the
presence of terbium ions in unsymmetrical environments.
A very broad peak indicates simultaneous emission from
site with different crystal field splitting [26]. Therefore,
the present investigation claims the synthesis of Eu+++
and Tb+++ doped Y2O3 phosphor nanoparticles for their
potential applications with continuous emission proper-
ties.
4. Conclusion
Europium and terbium ions have been incorporated into
Y2O3 matrix by hydrothermal process using yttrium oxo
Table 1. Comparative study of Eu+++/Y2O3 and Tb+++/Y2O3
nanoparticles synthesized by hydrothermal method.
Hydrothermal
Process Eu+++/Y2O3 (0.2M) Tb+++/Y2O3(0.2M)
Time XRD
[Particle
size (nm)]
PL [Transitio n
Peaks (nm)]
XRD
[Particle size
(nm)]
PL [Transitio n
Peaks (nm)]
3 h 28
5D0→7F1
5D0→7F2
5D0→7F4 43
5D3→7F1
5D3→7F2
5D3→7F3
4 h 32
5D0→7F1
5D0→7F2
5D0→7F4 46
5D3→7F1
5D3→7F2
5D3→7F3
5 h 34
5D0→7F1
5D0→7F2
5D0→7F4 50
5D3→7F1
5D3→7F2
5D3→7F3

R. P. SINGH ET AL. 17
isopropoxide as precursor. In hydrothermal process the
particle size increased as the heating time increased but
less than other process. The crystallinity w as achieved at
300˚C that is unique in comparison to other synthetic
methods. The morphological aspect of the resulting
powders was examined by TEM which showed single
dispersed particles along with agglomerates. X-ray dif-
fraction indicated that all of these agglomerates consisted
of Y2O3 doped with Eu+++ ions and Tb+++ ions. The loca-
tion of rare earth (Eu+++ and Tb+++) in the particles has
been probed by examining the PL spectra of particles.
The powders annealed at 300˚C for 3 h, 4 h and 5 h,
showed the occupancy of Eu+++ ions and Tb+++ ions in
both symmetrical and unsymmetrical lattice positions by
the ions. In case of hydrothermal process, the broadened
peaks were observed which is similar to sample synthe-
sized by sol-gel method [22] and annealed at 800˚C.
5. Acknowledgements
Dr. Anjana Pandey is grateful to Department of Biotech-
nology (DBT) and Department of Science and Technol-
ogy (DST), New Delhi for granting the financial support.
REFERENCES
[1] V. A. Alexandria, “Research Opportunities for Materials
with Ultrafine Microstructures,” National Academy Press,
Washington DC, 1989.
[2] S. Shikao and W. Jiye, “Combustion Synthesis of Euro-
pium Activated Y2Al5O12 Phosphor Nanoparticles,” Jour-
nal of Alloys and Compounds, Vol. 327, No. 1-2, 2001,
pp. 82-86. doi:10.1016/S0925-8388(01)01399-8
[3] K. E. Gonsalves, G. Carlson, J. Kumar, F. Aranda and M.
J. Yacama, “Nanotechnology: Molecularly Designed Ma-
terials,” In: Gan-Moog Chow, K. E. Gonsalves (Eds.), Di-
vision of Polymeric Materials: Science and Engineering,
Inc., 210th National Meeting of the American Chemical
Society, Chiago, 20-24 August 1995.
[4] E. Giannelis, “Nanotechnology Molecularily Designed
Materials,” In: G.-M.Chow and K. E. Gonsalves, Eds.,
American Chemical Society, Washington DC, 1995.
[5] A. D. Yoffe, “Low-Dimensional Systems: Quantum Size
Effects and Electronic Properties of Semiconductor Mi-
crocrystallites (Zero-Dimensional Systems) and Some
Quasi-Two-Dimensional Systems,” Advance in Physics,
Vol. 42, No. 2, 1993, pp. 173-266.
doi:10.1080/00018739300101484
[6] C. R. Ronda, “Recent Achievements in Research on Phos-
phors for Lamps and Displays,” Journal of Luminescence,
Vol. 72-74, 1997, pp. 49-54.
doi:10.1016/S0022-2313(96)00374-2
[7] E. Zych, “On the Reasons for Low Luminescence Effi-
ciency in Combustion-Made Lu2O3:Tb,” Optical Materi-
als, Vol. 16, No. 4, 2001, pp. 445-452.
doi:10.1016/S0925-3467(01)00009-X
[8] C. J. Summers, IDW’96 Proceedings, Vol. 2, 18-20 No-
vember 1996, p. 13.
[9] A. Vecht, Extended Abstracts of Second International
Conference on the Science and Technology of Display
Phosphors, San Diego, 18-20 November 1996, p. 247.
[10] L. Sun, J. Yao, C. Liu, C. Liao and C. Yan, “Rare Earth
Activated Nanosized Oxide Phosphors: Synthesis and
Optical Properties,” Journal of Luminescence, Vol. 87-89,
2000, pp. 447-450. doi:10.1016/S0022-2313(99)00471-8
[11] Y. L. Soo, S. W. Huang, Y. H. Kao, V. Chhabra, B. Kul-
kami, J. V. D. Veliadis and R. N. Bhargava, “Controlled
Agglomeration of Tb-Doped Y2O3 Nanocrystals Studied
by X-Ray Absorption fine Structure, X-Ray Excited Lu-
minescence, and Photoluminescence,” Applied Physics
Letters, Vol. 75, No. 6, 1999, pp. 2464-2466.
doi:10.1063/1.125049
[12] B. K. Gupta, D. Haranat, S. Saini, V. N. Singh and V.
Shanker, “Synthesis and Characterization of Ultra-Fine
Y2O3:Eu+++ Nanophosphors for Luminescent Security Ink
Applications,” Nanotechnology, Vol. 21, No. 5, 2010, p.
055607. doi:10.1088/0957-4484/21/5/055607
[13] I. L. Medintz, H. Mattoussi and A. R. Clapp, “Potential
Clinical Applications of Quantum Dots,” International
Journal of Nanomedicine, Vol. 3, No. 2, 2008, pp. 151-
167.
[14] T. Hirai, T. Orikoshi and I. Komasawa, “Preparation of
Y2O3:Yb, Er Infrared-to-Visible Conversion Phosphor
Fine Particles Using an Emulsion Liquid Membrane Sys-
tem,” Chemistry of Materials, Vol. 14, No. 8, 2002, pp.
3576-3583. doi:10.1021/cm0202207
[15] H. Eilers, “Synthesis and Characterization of Nanophase
Yttria Co-Doped with Erbium and Ytterbium,” Material
Letters, Vol. 60, No. 2, 2006, pp. 214-217.
doi:10.1016/j.matlet.2005.08.021
[16] G. De, W. Qin, J. Zhang, Y. Wang, C. Cao and Y. Cui,
“Upconversion Luminescence Properties of Y2O3:Yb3+,
Er3+ Nanostructures,” Journal of Luminescence, Vol. 119-
120, 2006, pp. 258.
[17] L. Yang, Y. Tang, X. Chen, Y. Li and X. Cao, “Synthesis
of Eu3+ Doped Y2O3 Nanotube Arrays through an Electric
Field-Assisted Deposition Method,” Material Chemistry
and Physics, Vol. 101, No. 1, 2007, pp. 195-198.
doi:10.1016/j.matchemphys.2006.03.006
[18] G. S. Wu, Y. Lin, X. Y. Yuan, T. Xie, B. C. Cheng and L.
D. Zhang, “A Novel Synthesis Route to Y2O3:Eu Nano-
tubes,” Nanotechnology, Vol. 15, No. 5, 2004, pp. 568-
571. doi:10.1088/0957-4484/15/5/029
[19] Z. Xu, Z. Hong, Q. Zhao, L. Peng and P. Zhang, “Prepara-
tion and Luminescence Properties of Y2O3:Eu+++ Nano-
rods via Post Annealing Process,” Journal of Rare Earths,
Vol. 24, No. 1, 2006, pp. 111-114.
doi:10.1016/S1002-0721(07)60336-6
[20] V. V. Rajasekharan and D. A. Buttry, “Electrochemical
Synthesis of Yttrium. Oxide Nanotubes,” Chemistry of
Materials, Vol. 18, No. 19, 2006, pp. 4541-4543.
doi:10.1021/cm061024t
[21] X. Li, Q. Li, J. Wang and J. Li, “Hydrothermal Synthesis
of Er-Doped Yttria Nanorods with Enhanced red Emis-
sion via Upconversion,” Journal of Luminescence, Vol.

R. P. SINGH ET AL.
18
124, No. 2, 2007, pp. 351-356.
doi:10.1016/j.jlumin.2006.04.007
[22] A. Pandey, A. Pandey, M. K. Roy and H. C. Verma,
“Sol-Gel Synthesis and Characterization of Eu+++/Y2O3
Nanophosphore by an Alkoxide Precursor,” Material Che-
mistry and Physics, Vol. 96, No. 2-3, 2006, pp. 466-470.
doi:10.1016/j.matchemphys.2005.07.037
[23] S. Kim, Y. T. Lim, E. G. Soltesz, A. M. De Grand, J. Lee,
A Nakayama, J. A. Parker, T. Mihaljevic, R. G. Laurence,
D. M. Dor, L. H. Cohn, M. G. Bawendi and J. V. Fran-
gioni, “Near-Infrared Fluorescent Type II Quantum Dots
for Sentinel Lymph Node Mapping,” Nature Biotechnol-
ogy, Vol. 22, 2004, pp. 93-97. doi:10.1038/nbt920
[24] J. A. Nelson, E. L. Brant and M. J. Wagner, “Nanocrystal-
line Y2O3:Eu Phosphors Prepared by Alkalide Reduc-
tion,” Chemistry of Materials, Vol. 15, No. 3, 2003, pp 688-
693. doi:10.1021/cm0207853
[25] F. Paraspour, D. F. Kelley and R. S. Williams, “Spectros-
copy of Eu+++-Doped PtS2 Nanoclusters,” Journal of Phy-
sical Chemistry, Vol. 102, No. 41, 1998, pp. 7971-7977.
doi:10.1021/jp982628q
[26] K. Kömpe, O. Lehmann and M. Haase, “Spectroscopic
Distinction of Surface and Volume Ions in Cerium(III)-
and Terbium(III)-Containing Core and Core/Shell Nano-
particles,” Chemistry of Materials, Vol. 18, No. 18, 2006,
pp. 4442-4446. doi:10.1021/cm060857g