World Journal of Nano Science and Engineering, 2012, 2, 201-205 Published Online December 2012 (
Photoluminescence Properties of LaF3:Ce Nan oparticle s
Embedded in Polyacrylamide
Thiruvalankadu Krishnamoorthy Srinivasan1*, Balasubramaniam Venkatraman1, Durairaj Ponraju2,
Akhilesh Kumar Arora3
1Radiological Safety and Environmen t Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, India
2Physical Chemistry Section, Reactor Engineering Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, India
3Condensed Matter Physics Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, India
Email: *
Received August 1, 2012; revised August 29, 2012; accepted September 6, 2012
Oleic acid coated LaF3:Ce nanoparticles were synthesized and embedded in polyacrylamide through a two-step proce-
dure. In the first step nanoparticles were synthesized by adopting co-precipitation technique and in the second step,
nanoparticles were embedded in polyacrylamide (PAM) hydro-gel through the so lution route. Nanoparticels were char-
acterized for their crystal structure, particle size, organic coating and photoluminescence behavior using X-ray diffrac-
tion, SEM, TEM, FTIR and photoluminescence spectroscopy. Size of nanoparticles was estimated using the Scherer
formula. Polymer nano composite (PNC) material was synthesized with two different weight percent of the nano pow-
der viz 1.634% (termed as NG1) and 0.1664% (termed as NG2). The nanoparticle-polymer composite exhibits emis-
sions at 308 and 370 nm. A comparison of the emission spectrum of LaF3:Ce nano-powder pellet with that o f the com-
posite suggests a suppression of emission from the PAM host in the composite.
Keywords: Lanthanum Fluoride Cerium; Polyacrylamide; Oleic Acid; Photoluminescence; Nanocomposite
1. Introduction
In the quest for new optical materials, polymer nano-
composites (PNC) are currently being explored. Lumi-
nescent PNC materials are inexpensive and can be syn-
thesized in different shapes and sizes. These materials
find applications in sensing high energy X- and gamma
radiation. In this context rare-earth doped nanophosphor
with sizes <100 nm in transparent polymer composites
have been studied. In order to protect the nanophosphor
material from the host environment and to achieve better
dispersibility in the monomer, these are coated with or-
ganic materials such as oleic acid. These nanoparticles
possess unique chemical and optical features such as low
toxicity, characteristic narrow emission, and excellent
photo stability [1].
Cerium doped Lanthanum halides display desirable
high light yields with fast decay component. Inorganic as
well as organic surfactant capped LaF3:Ce have been
extensively studied [2-6]. Considerable interest is shown
in surface modification of luminescent nanoparticle with
functional groups, which in creases possibility of uniform
embedding in different transparent polymer hosts [7-9].
The methods involve synthesizing nanoparticles first and
then blend into the required matrices through intimate
mixing of nanoparticles with monomer solution and sub-
sequent immobilization through polymerization. In this
work, we report the synthesis and embedding of oleic
acid coated LaF3:Ce nanoparticles in polyacrylamide host
medium. The photoluminescent characteristics of the syn-
thesized polymer nanocomposite are presented.
2. Experimental Details
LaF3:Ce embedded polyacrylamide (PAM) disc was
made in two steps. LaF3:Ce was synthesized by co-pre-
cipitation technique. First, oleic acid coated nano cerium
doped lanthanum fluoride was synthesized as ref [10].
Next, the powder was embedded inside PAM disc using
a slightly different procedure that reported in [11]. A
solution containing 8 g of arylamide in 10 g of deionized
water was prepared. LaF3:Ce embedded discs were syn-
thesized using the acrylamide solution with two d ifferent
nano-powder concentration of 16.6 and 1.75 mg/ml. The
mixtures were thoroughly stirred for 30 minutes and
placed in an ultrasonic water bath for 20 minutes for the
gas bubbles, if any, to escape. Then the mixture was po-
lymerized in the gamma chamber (GC 5000) containing
4.8 TBq activity of Cobalt-60 radioisotope and irradiated
for four minutes to a gamma dose of 221 Gy. The po-
*Corresponding a uthor.
opyright © 2012 SciRes. WJNSE
lymerized samples were taken dried in a vacuum oven at
90˚C for 4 h. The discs were circular in shape with 2 cm
diameter and 1 cm thickness. The weight percent of the
nano powder in the polymer composites were 1.634%
(termed as NG1) and 0.1664% (termed as NG2) respec-
tively. The NG1 disc was little opaque while NG2 disc
was a completely transparent. Similarly another pure
polyacrylamide disc without LaF3:Ce (blank-PAM) was
prepared for comparing the optical behavior.
The structural characterization was carried out using
X-ray diffraction measurements using a Shimadzu (XRD-
6000) diffractometer equipped with a CuKα (1.5406 Å)
X-ray source. The micrographs of as prepared samples
were obtained using field emission scanning electron
microscope [FESEM, ZEISS]. TEM [JEOL 2000 EX II],
FTIR spectra were recorded using HORIZON MB3000
ABB spectrophotometer in order to check the surface
organic coating and the spectrum was measured in trans-
mission mode using KBr disc. In order to prepare the
TEM specimen, the powder was ultra-sonicated in
methanol medium and one drop of the suspension was
loaded on to carbon coated grids. Th is was dried under a
lamp for over 12 hours and loaded into the specimen
carousel of the JEOL 2000 EX II TEM operated at 200
kV. Electron diffraction, diffraction contrast and phase
contrast imaging was also carried out. Photolumines-
cence (PL) measurements on the discs were carried out
using a SHIMADZU spectrophotometer [Flourolog-RF-
5301PC] in the range of 200 - 400 nm at 1.5 nm slit
widths and in high sensitivity mode.
3. Results and Discussion
Figure 1 shows the XRD pattern of oleic acid coated
nanoparticles. The peak positions and intensities agree
well with the data reported in the JCPDS standard card
(32-0483) for pure hexagonal LaF3:Ce particles. The
large width of the diffraction peaks is an indication of the
nanosize of the particles. The structure was determined to
be hexagonal with a = 7.1889 and c = 7.3231 Å. The
sizes of the nanoparticles were calculated from the XRD
data based on the Debye-Scherer formula. The results
showed that the oleic-coated nanoparticle size was 11
Figure 2(a) shows the FESEM micrograph of Ce-
doped LaF3 nanoparticles synthesized at 70˚C. The parti-
cles were of spherical and slightly oblong in shape with
the diameter ranging between 8 and 36 nm. However
some agglomeration of particles leading to bigger parti-
cle sizes was also observed. The modified approach of
Feng Wang et al. [3] yielded primary particles of smaller
size. Figure 2(b) show s the size distribution of the parti-
cles. The 60 and 85 nm particles are essentially aggre-
gates and don’t correspond to the individual particles. It
is clear that majority of particles were between 8 and 11
10 20 30 40 50 60 70 80
221 220
Intensity (arb.units)
2 (deg)
Figure 1. XRD pattern of LaF3:Ce nanoparticles. The re-
ported reference pattern is also shown for comparison
(JCPDS card No. 32-0483).
10 20 30 40 50 60 70 80
Number of Particles
Pa r tic le S iz e (n m)
Figure 2. (a) FESEM micrograph image of LaF3:Ce nano-
particles; (b) The size distribution plot of FESEM micro-
graph image of LaF3:Ce nanoparticles.
nm sizes. In order to know with what sizes the particles
have formed, a size distribution plot was arrived at by
analyzing the obtained SEM micrograph using the Image
J software. As the particle sizes are small, more weight
% can be incorporated in the polymer retaining the opti-
Copyright © 2012 SciRes. WJNSE
cal transparency.
Figure 3 shows the high resolution TEM image of as
synthesized Oleic acid coated LaF3:Ce nanoparticles. The
coating thickness was found to be around 3.5 nm. It can
be seen that the nanoparticles have a certain degree of
Figure 4 shows the FT-IR spectra of both pure oleic
acid (curve a) and oleic acid coated LaF3:Ce nanoparti-
cles (curve b). In curve a&b, the two band at 2922 and
2856 cm–1 are corresponds to CH2 asymmetric and sym-
metric stretching vibrational frequency respectively [12].
A weak band at 3011 cm–1 indicates the presence of un-
saturated alkene (=C-H) group. In curve (b) presence of
CH2 stretching vibrational peak reveals the presence of
organic surfactant on surface of LaF3:Ce nano particle. In
curve (a) strong peak at 1708 cm–1 attributed to stretch-
ing vibration of C=O group. When compared to curve (a)
in curve (b) the reduction peak intensity of 1708 cm–1
C=O stretching vibration and appearance of two new
absorption peaks at 1582 and 1546 cm–1 are due to car-
boxylate formation on the nano LaF3:Ce surface, which
are attributed to the characteristic of the asymmetric
(COO) stretch and the symmetric (COO) stretch [13].
The disappearance of C=O stretching vibration and
presence of two COO stretching confirms that Oleic
acid is not physically adsorbed on the surface of LaF 3:Ce
nano particle, its coordinated through carboxylate group
with nano particle. These results confirm that Oleic acid
molecules were chemisorbed on nano LaF3:Ce particles.
Figure 5 shows the excitation and emission spectrum
of the 5 mole % Ce-doped LaF3 nanoparticle pellet. The
excitation spectrum was recorded for the sample by
scanning the excitation wavelength from 200 nm to 280
nm, while the emission monochromator was fixed at 306
nm with spectral bandpass at 1.5 nm. The excitation peak
was found to be at 251 nm (curve a), which closely
agrees with the position of lower energy levels in the 4f
to 5d (4.96 eV) configuration of cerium. The emission
spectrum was acquired by exiting the pellet at 251 nm
wavelength in the region between 265 nm to 400 nm
with the same spectral band pass. The broad emission
Figure 3. HR-TEM image of the oleic acid coated LaF3:Ce
4000 3500 3000 2500 2000 1500 1000
721 721
Wave number (cm-1)
Transmittance (%)
Figure 4. FTIR spectrum of (a) oleic acid and (b) oleic acid
coated LaF3:Ce nano-powder.
220 240 260 280 300320 340 360 380 400
Inte n sity (a rb.u nits)
Wav elength (nm)
Figure 5. PL excitation and emission spectra of oleic acid
coated 5 mole % Ce3+-doped LaF3 nanoparticle pellets (a)
Excitation (Em = 306 nm); (b) Emission (Ex = 251 nm).
peak found at 306 nm (curve b) can be ascribed to 5d to
4f transitions revealing the nature of Ce3+ emission [14].
One can see that the emission from the pellet is intense.
The presence of hydrocarbon chains on the surface might
quench the output light intensity by radiation less energy
Figure 6 shows the excitation and emission spectra of
the blank-PAM, LaF3:Ce embedded PAM-NG1 and NG2
discs. The spectra of blank-PAM and nanocomposite
materials were recorded in the region 220 - 400 nm.
Curves a and b respectively correspond to the excitation
and emission of blank-PAM disc. The emission peak at
370 nm corresponds to the 253 nm absorption of
blank-PAM. Curves c (NG2), e (NG1) and d (NG2), f
(NG1) respectively correspond to the excitation and
emission spectra of doped-PAM discs. One can see that
the emission spectra of the composite exhibit two peaks,
one at 308 nm and the other at 370 nm. The spectral po-
sitions slightly sh ift towards the blue region as compared
to that of pure LaF3:Ce nano-powder pellet. It is impor-
tant to point out that the 253 nm excitation of the nano
Copyright © 2012 SciRes. WJNSE
220 240 260 280 300 320 340 360 380 400
Inte nsity (arb.units)
W ave le n gth (n m)
Figure 6. Excitation and emission spectra of blank PAM
and LaF3:Ce3+ embedded PAM discs. (a) Blank PAM exci-
tation (Em = 370 nm); (b) Blank PAM emission (Ex = 253
nm); (c) and (e) NG2 and NG1 excitation (Em = 308 nm); (d)
and (f) NG2 and NG1 emission (Ex = 253 nm).
composite gives much lower intensity of the 370 nm
emission compared to that of blank-PAM. This suggests
that doping the PAM matrix by the nanoparticles causes
suppression of the photoluminescent emission from the
polymer host. The 370 nm PL emission of the host ma-
trix is further suppressed when the doping concentration
is increased (curve f). Thus the present results suggest
that only the nano-particles are selectively excited while
the host excitation is transferred to the nanoparticles.
This property may be useful where interference from the
host is to be avoided. Lower intensity of the 308 nm
emission from the nanocomposite disc NG1 might be due
to larger opacity. This suggests that low-doped NG2
translucent composites can be used as efficient intrinsic
PL emission materials with reduced interference from the
host. Figures 7(a) and (b) show the photographs of the
synthesized PAM discs. It is clear that NG2 disc is
translucent and NG1 disc is little o paque.
4. Conclusion
LaF3:Ce embedded in polyacrylamide discs were synthe-
sized by a simple two step procedure. The particle size
was estimated to be of 11 nm from XRD analysis. The
FESEM micrograph confirmed that the particle sizes
were distributed between 11 and 85 nm. FTIR spectra con-
firmed the presence of hydrocarbon chains surrounding
the nano particles. TEM image analysis confirmed the
presence of 3.5 nm thickness coating. The photolu-
minescent study confirmed the presence of the nano-
phosphor in the organic matrix. Although LaF3:Ce
nanoparticles and PAM exhibit characteristic PL emission
at 308 and 370 nm respectively, both these materials ha ve
excitation peaks at 253 nm. The nanocomposite is found
to have reduced emission from the host matrix as com-
Figure 7. Photographs of polymer nanocomposite discs (a)
NG1, (b) NG2.
pared to pure PAM disc, suggesting selective excitation of
the nanoparticles and suppression of the PL from the
5. Acknowledgements
The authors thank S. C. Chetal, Director IGCAR for his
support and encouragement. The authors also thank H.
Krishnan for the help in synthesis and Dr. B. S. Pani-
grahi for the help during PL measurements. The authors
also thank S. Kalavathi for the help rendered during
XRD measurements and Dr. M. Kamarudin during the
FESEM measurements. The authors also thank Dr. Mo-
handas, Dr. Diwakar and Chanchal Gosh for their help in
TEM measurements and analysis. The authors also thank
Dr. V. Meenakshisundaram and Dr. M. T. Jose for their
useful discussions and support.
[1] M.-Y. Xie, L. Yu, H. He and X.-F. Yu, “Synthesis of
Highly Fluorescent LaF3:Ln3+/LaF3 Core/Shell Nanopar-
ticles by a Surfactant-Free Aqueous Solution Route,”
Journal of Solid State Chemistry, Vol. 182, No. 3, 2009,
pp. 597-601. doi:10.1016/j.jssc.2008.12.011
[2] S. S. Mou, M. J. Islam and A. B. M. Ismail, “Photolumi-
nescence Properties of LaF3-Coated Porous Silicon,” Ma-
terials Sciences and Applications, Vol. 2, No. 6, 2011, pp.
[3] F. Wang, Y. Zhang, X. P. Fan and M. Q. Wang, “Facile
Copyright © 2012 SciRes. WJNSE
Copyright © 2012 SciRes. WJNSE
Synthesis of Water-Soluble LaF3:Ln3+ Nanparticles,” Jour-
nal of Materials Chemistry, Vol. 16, No. 11, 2006, pp.
1031-1034. doi:10.1039/b518262j
[4] J. Stouwdam and F. van Veggel, “Near-Infrared Emission
of Redispersible Er3+, Nd3+, and Ho3+ Doped LaF3 Nano-
particles,” Nano Letters, Vol. 2, No. 7, 2002, pp. 733-737.
[5] G. S. Yi and G. M. Chow, “Colloidal LaF3: Yb, Er, LaF3:
Yb, Ho and LaF3: Yb, Tm Nanocrystals with Multicolor
up Conversion Fluorescence,” Journal of Materials Che-
mistry, Vol. 15, No. 41, 2005, pp. 4460-4464.
[6] T. Kezuka, M. Konishi, T. Isobe and M. Senna, “Prepara-
tion and Properties of Nanocrystalline ZnS: Mn-Polymer
Composite Silms,” Journal of Luminescence, Vol. 87, No.
89, 2000, pp. 418-420.
[7] A. Klausch, H. Althues, C. Schrage, P. Simon, A. Szat-
kowski, M. Bredol, D. Adame and S. Kaskel, “Prepara-
tion of Luminescent ZnS:Cu Nanoparticles for the Func-
tionalization of Transparent Acrylate Polymers,” Journal
of Luminescence, Vol. 130, No. 4, 2010, pp. 692-697.
[8] V. Kalima, I. Vartiainen, T. Saastamoinen, M. Suvanto,
M. Kuittinen and T. T. Pakkanen, “UV-Curable ZnS/Poly-
mer Nanocomposite for Replication of Micron and Sub-
micron Features,” Optical Materials, Vol. 31, No. 10, 2009,
pp. 1540-1546. doi:10.1016/j.optmat.2009.03.003
[9] Y. Chen, X. Ji, Q. Sun, S. Jiang and B. Jiang, “A Novel
Route for the Preparation of CdS Nanocrystal—Poly
(Acrylic Acid) Composites Using γ-Radiation,” Journal
of Non-Crystalline Solids, Vol. 311, No. 3, 2002, pp. 314-
317. doi:10.1016/S0022-3093(02)01854-9
[10] T. K. Srinivasan, B. Venkatraman, D. Ponraju, M. Kama-
rudin and A. K. Arora, “Synthesis and Characterization of
Surface Modified LaF3:Ce Nano Particles,” International
Conference on Nanoscience, Engineering and Technology
(ICONSET), Chennai, 28-30 November 2011, pp. 528-
531. doi:10.1109/ICONSET.2011.6168023
[11] N. Pewda, L. Mihut, I. Baltog, T. Velula and V. Teodo-
rescu, “Optical Properties of Low-Dimensional PbI2 Par-
ticles Embedded in Polyacrylamide Matrix,” Journal of
Optoelectronics and Advanced Materials, Vol. 8, No. 3,
2006, pp. 909-913.
[12] N. Q. Wu, L. Fu, M. Su, M. Aslam, K. C. Wong and V. P.
Dravid, “Interaction of Fatty Acid Monolayers,” Nano
Letters, Vol. 4, No. 2, 2004, pp. 383-386.
[13] J. S. Wang, J. Hu, D. H. Tang, X. H. Liu and Z. Zhen,
“Oleic Acid Modified LaF3: Er, Yb Nanocrystals and
Their Polymer Hybrid Materials for Potential Optical-
Amplification Applications,” Journal of Materials Che-
mistry, Vol. 17, No. 16, 2007, pp.1597-1601.
[14] P. Dorenbos, “5D-Level Energies of Ce3+ and the Crys-
talline Environment. I. Fluoride Compounds,” Physical
Review B, Vol. 62, No. 23, 2000, pp. 15640-15649.