Silica glasses and siliceous powders activated with CeO2:Ln3+ (Ln ¹ Ce) nanoparticles were synthesized by the sol-gel method and their structural and spectral-luminescent properties were investigated. It is shown that the main features of the Ln3+ ions are a high relative intensity of magnetic dipole transitions  and sufficiently effective sensitization of their luminescence with labile photoreduced (Ce4+)- ions by means of superexchange mechanism or/and by transfer of electron

Khottchenkova, T.G.

Kouhar, V.V.

Malashkevich, G.E.

Pestryakov, E.V.

Sigaev, V.N.

English

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 3 No 2, 02NAESF11(2pp) (2014) 
 
 
2304-1862/2014/3(2)02NAESF11(2) 02NAESF11-1  2014 Sumy State University 
Optical Materials Activated with CeO2:Ln3+ Nanoparticles 
 
G.E. Malashkevich1,*, T.G. Khottchenkova1, V.V. Kouhar1, V.N. Sigaev2, E.V. Pestryakov3 
 
1 B.I. Stepanov Institute of Physics, NAS of Belarus, 68, Nezalezhnastsi Av., 220072 Minsk, Belarus 
2 D.I. Mendeleev University of Chemical Technology, 9, Miusskaya Sq., 125047 Moscow, Russia 
3 Institute of Laser Physics, SB RAS, 13/3, Acad. Lavrent’ev Av., Novosibirsk, 630090, Russia 
 
(Received 16 July 2014; published online 29 August 2014) 
 
Silica glasses and siliceous powders activated with CeO2:Ln3+ (Ln  Ce) nanoparticles were synthesized 
by the sol-gel method and their structural and spectral-luminescent properties were investigated. It is 
shown that the main features of the Ln3+ ions are a high relative intensity of magnetic dipole transitions  
and sufficiently effective sensitization of their luminescence with labile photoreduced (Ce4+) ions by means 
of superexchange mechanism or/and by transfer of electron. 
 
Keywords: Oxide nanoparticles, Luminescence, Structure of optical centers, Transfer of electron excita-
tions. 
 
 PACS numbers: 42.70. – a, 61.46. + w, 78.55. – m 
 
 
                                                          
* g.malashkevich@ifanbel.bas-net.by 
1. INTRODUCTION 
 
In the middle of the 90th years, we discovered that 
quantum yield of Ce3+ ions luminescence in the silica 
gel-glasses containing triply and quadruply charged 
cerium ions can exceed up to some times the fraction of 
exciting radiation quanta absorbed by Ce3+ [1]. The 
effect stimulated us to more intimate investigation of 
the cerium optical centers in the glasses. As a result of 
the fulfilled work we discovered that this effect is 
caused by transfer of excitation in conditions of ex-
change-resonance interaction from the labile photore-
duced (Ce4+) ions to the stable Ce3+ ions in the CeO2 
nanoparticles whose Ce4+ ions are partially substituted 
by Ce3+ ions. It opens wide possibilities for creation of 
optical materials with the nanoparticles as the Ce3+ 
ions can be substituted by another Ln3+ ions as well as 
a number of other luminescent ions. Therefore, the aim 
of the report is to show the “spectroscopic and photo-
physical potentials” of CeO2-nanoparticles formed in 
silica glasses and siliceous powders with partial substi-
tution of the cerium ions by other rare earth ions. 
 
2. MATERIALS AND EXPERIMENTAL 
 
The glass samples were prepared by known sol-gel 
method [2]. Activation of the glass samples was carried 
out by impregnation of the obtained xerogels with the 
water-alcohol solution of cerium and other rare earth 
salts. In some cases, solution of alkaline or alkaline-
earth elements salts was similarly doped for compensa-
tion of the local charge. Then, the dehydrated samples 
were vitrified in oxygen or in air to a state of transpar-
ent glass. The powder samples were prepared by enter-
ing of the salts solutions into the sol, grinding of the 
xerogel obtained to the ultradispersed state and their 
heat-treatment in the corresponding redox conditions. 
At necessity, the samples were additionally heat-
treated in hydrogen to reduce the Ln4+ ions. 
The investigation of samples was carried out by an 
X-ray diffraction, small-angle neutron scattering, scan-
ning electron microscope and spectral-luminescent 
methods. 
 
3. RESULTS AND DISCUSSION 
 
Fig. 1 shows the X-ray diffraction patterns of trans-
parent oxygen-vitrified silica glass doped with Ce and 
Ho in concentrations of 31020 and 41019 ions/cm3 (a) 
and air-annealed siliceous powder including the dopes 
in concentrations of 21021 and 21020 cm3 (b) respec-
tively. Comparison of locations and relative intensities 
of the main displayed Bragg reflections with the data of 
the JCPDS-1998 Powder Diffraction File testify that 
they correspond to the CeO2 cubic lattice with space 
group of symmetry 5
hO  Fm3m. Additional doping of 
the samples with Cs or Mg for the local charge compen-
sation practically doesn’t influence on the diffraction 
patterns. As small-angle neutron scattering investiga-
tion showed, the mean sizes of the nanoparticles are 
close to 10 nm for the glass. At that, entering of the 
local charge compensator leads to the limitation of  the  
 
Fig. 1  X-ray diffraction patterns of (a) silica glass and (b) 
siliceous powder containing nanoparticles CeO2:Ho. 
 = 0.154184 nm 
 
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 G.E. MALASHKEVICH, T.G. KHOTTCHENKOVA, ET AL. PROC. NAP 3, 02NAESF11 (2014) 
 
 
02NAESF11-2 
nanoparticles sizes. As for the powder obtained, the 
microscopic analysis showed that it represents agglom-
erates with sizes about 1 m including individual 
spherical particles with sizes about 50 nm. It should be 
noted that due to the presence of significant share of 
SiO2, we suppose that the individual particles are sur-
rounded by the SiO2 shell, the powder relatively easily 
vitrifies to the ceramics. 
Fig. 2 shows luminescence spectra of oxygen-
vitrified silica glasses activated with CeO2:Ln nanopar-
ticles (curves 1 and 3) where Ln = (a) Eu, (b) Nd, (c) Ho 
and (d) Sm and Ln3+ ions (curve 2) These spectra are 
corrected with regard to the spectral sensitivity of the 
recording system and normalized by reducing their 
maximum to unity. As it is seen, the luminescence  
 
Fig. 2  Corrected luminescence spectra of silica glasses acti-
vated with (1, 3) CeO2:Ln nanoparticles and (2) isolated Ln3+ 
ions Ln = (a) Eu, (b) Nd, (c) Ho and (d) Sm. exc (nm): 266 (1a, 
3a); 320 (1c, 1d); 370 (1b); 395 (2a); 400 (2d); 450 (2c); 580 (2b). 
T = 30K (1a, 3a) and 298K for all other curves 
 
caused by Ln3+ ions incorporated in the nanoparticles is 
characterized by structural spectra typical for the crys-
tals in contrast to the spectra caused by isolated Ln3+ 
ions. At that, the share of quanta radiated by the first 
indicated ions in the magnetic-dipole transitions signif-
icantly higher than radiated in the electric-dipole tran-
sitions (cf. curves 1 and 2 in Fig. 2a and Fig. 2d). Given 
feature testifies to the possibility to increase the quan-
tity of laser channels for account of the magnetic-dipole 
transitions for the materials activated with the 
CeO2:Ln3+ nanoparticles. Similar luminescence spectra 
are character for the corresponding powders too. 
 
Comparison of luminescence intensity of the Ln3+ 
ions in the nanoparticles at excitation through the 
above indicated sensitizer at decreasing of temperature 
from 298 to 77K shows that the intensity decreases for 
the Sm3+ and Eu3+ significantly larger than for the 
Nd3+ and Ho3+ ions. As the samarium and europium 
ions can relatively easily reduce to the double-charged 
state, the indicated fact permits us to conclude about 
essential role of charge transfer in the processes of the 
ions luminescence sensitization. Moreover, the lumi-
nescence of highly-symmetric photoreduced (Eu3+) ions 
is characterized by narrow band centered at 666 nm 
that can be observed at low temperatures ( 30K) as it 
is confirmed by Fig. 2a, curve 3. 
A reduction of quadruply charged cerium to triply 
charged state in the nanoparticles by saturation of the 
glasses and powders with hydrogen permits to reach an 
efficiency of sensitization of their Ln3+ ions lumines-
cence by the stable Ce3+ ions close to 100 % in some 
cases. However, the luminescence spectra of Ln3+ ions 
in the nanoparticles with stable reduced Ce3+ ions can 
significantly differ from their spectra in the initial 
nanoparticles. 
Here it should be noted that at co-existence in the 
glasses of isolated Ce4+Ln3+- and Ln3+-centers besides 
of the CeO2:Ln3+ nanoparticles such glasses possess by 
strong dependence of their luminescence spectrum on 
excitation wavelength. 
 
4. CONCLUSION 
 
In a process of the sol-gel synthesis of silica glasses 
and siliceous powders co-doped with Ce and Ln  Ce, 
the formation of the CeO2:Ln3+ nanoparticles with the 
5
hO  Fm3m space group symmetry is possible. It can 
operate by sizes of the nanoparticles with the help of 
extrinsic compensators of local charge. Due to the 
spherical shape and presence of such binding agent as 
SiO2 the powders may be promising precursors for 
obtaining of laser ceramics able to stimulated radiation 
in the magnetic-dipole transitions of rare earth ions. 
 
AKNOWLEDGEMENTS 
 
This work was partly supported by the Belarusian 
Foundation for Basic Research (grant F12SB-055)  and 
Program of Basic Research SB RAS  NAS of Belarus 
(grant 17). 
 
REFERENCES 
 
1. G.E. Malashkevich, E.N. Poddenezhnyi, I.M. Mel’nichenko, 
A.A. Boiko, L.G. Brazhnik, Opt. Spectros. 78, 74 (1995). 
2. G.E. Malashkevich, E.N. Poddenezhny, I.M. Mel’nichenko, 
A.A. Boiko, J. Non-Cryst. Solids 188, 107 (1995).  
 
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Optical Materials Activated with CeO2:Ln3+ Nanoparticles

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