New Journal of Glass and Ceramics, 2011, 1, 34-39
doi:10.4236/njgc.2011.12006 Published Online July 2011 (http://www.SciRP.org/journal/njgc)
Upconversion Luminescence of Er3+/Yb3+
Co-Doped Sb2O3-WO3-Li2O Antimon ate Glasses
Deqiang Wang, Junjie Lu, Zhen Zhang, Yingfei Hu, Zhiling Shen
Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China Univer-
sity of Science and Technology, Shanghai, China.
Received May 13th, 2011; revised June 10 th, 2011; accepted Jun e 17th, 2011.
ABSTRACT
A series of Er3+/Yb3+ co-doped Sb2O3-WO3-Li2O glasses were prepared. Intense green upconversion fluorescence was
observed near 524 and 544 nm under excitation at 980 nm. The upconversion process was proved to be a two-photon
absorption process. The upconversion fluorescence efficiency was enhanced by increasing introduction concentration
of Yb3+ ions. The low maximum phonon energy of the glasses indicated that the glasses were good potential for upcon-
version optical devices.
Keywords: Upconversion Fluorescence, Glasses, Laser
1. Introduction
Recently, with the increasing requirement for laser d iode
(LD), magneto-optical disk and optical media, more and
more attention has been focused on searching for lumi-
nescence materials with high upconversion efficiency
[1-3]. The upconversion is greatly affected by sensitizing
combination, pumping laser wavelength and conversion
passage, which makes the host materials for rare earth
(RE) ions and the dopant ions as the absorption and
emis sion center s ver y impor tant [4,5]. Glasses have been
selected as the potential host materials because of its low
phonon energy which can reduce the multiphonon relax-
ation (MPR) and thus achieves strong upconversion lu-
minescence. Though fluoride glasses have been studied
because of their low phonon energies, oxide glasses are
more appropriate for practical applications due to their
high chemical durability and thermal stability. Although
silicate glasses are stable, upconversion fluorescence is
difficult to observe in silicate glasses because o f its high
maximum phonon energy [6]. Nowadays, tellurite and
antimonate glasses are of growing interest due to their
relative low phonon energy, high refractive index, good
corrosion resistance, thermal and chemical stability. The
antimonate glasses are more stable against the pumping
light, possess high refractive index and are transparent up
to the far infrared wavelengths which makes them suita-
ble for hosting the rare earth ions to give out high lumi-
nescence efficiency in the visible and NIR regions
[7-10].
Triply ionized Er3+, Ho3+, Tm3+, Nd3+ ions of the lan-
thanide ser ies have b ee n wid el y stud ied for upc onversion
processes in various glass hosts. Erbium ion (Er3+) has
been recognized as one of the most efficient ions for ob-
taining frequency upconversion [11,12]. In order to im-
prove the pumping efficiency of 980 nm LD, the sensiti-
zation of Er3+ doped materials with Yb3+ ions is a popular
way to increase the optical pumping efficiency because
Yb3+ ions exhibits an intense broad absorption cross sec-
tion between 870 and 1050 nm [13], while Er3+ has low
absorption at 980 nm.
In this paper, we report our progress on the fabrication
and upconversion luminescence characterization of a
novel Er3+/Yb3+ co-doped Sb2O3-WO3-Li2O (SWL)
glasses. The phonon energy of this glass has been pre-
dicted from the FT -IR spectra. The purpose of this paper
is to develop a new antimony glass with low phonon
energy, and understanding of the upconversion behavior
in this glassy host for predicting its potential laser prop-
erties.
2. Experimental
Antimonate glasses were prepared by melting the reagent
grade Sb2O3, Li2CO3, WO3, Er2O3 and Yb2O3 as the
starting materials. The starting materials were sufficient-
ly mixed and grinded, then were melted at 1000˚C -

Upconversion Luminescence of Er3+/Yb3+ Co-Doped Sb2O3-WO3-Li2O Antimonate Glass es
35
1100˚C for 10 min, followed by an annealing at 270˚C
for 3 h in a muffle furnace to eliminate the internal stress,
then slowly cooled down to the room temperature.
Compositions chosen in the present study are shown in
Table 1. Finally, glass samples were cut, ground and
polished for the following measurement.
Thermal stability analyses of the glasses were deter-
mined by using a CRY-2CRY-1WRT-1 thermal ana lysis
(DTA) at a heating rate of 10˚C /min from ro om t emper-
ature to 800˚C. IR transmission spectra were recorded
between 400 and 4000 cm-1 (Nicolet 6700). UV trans-
mission spectra were recorded between 300 and 1000 nm
(Shanghai Lengguang S54). For Er3+/Yb3+ co-doped an-
timonate bulk glasses, the upconversion luminescence
spectra were obtained with a spectrofluorimeter (Jobin
Yvon Fluorolog3-p, France) upon excitation of 980 nm
LD with a maximum power of 1 W. The glass was posi-
tioned so that the pump beam was allowed to be incident
at the edge of the glass sample, and the optical path of
emitted light through the sample to the detector was ap-
proximately 1 mm.
3. Results and Discussion
3.1. DTA and XRD Spectra
The DTA spectra of 0.25Er3+/0.75Yb3+ co-doped
Sb2O3-WO3-Li2O glasses (mol%) (No. 7) was shown in
Figure 1. From the figure, it can be seen that the transi-
tion temperature and melting temperature of this glass is
272˚C and 584˚C respectively. The 550˚C point is the
beginning of melting temperature point. There is an ob-
vious crystallization peak at 385˚C (Tx). The difference
between the glass transition temperature (Tg) and the
onset crystallizatio n temperature (Tx), ΔT = Tx – T g has
been frequently quoted as a rough indicator of glass sta-
bility against crystallization [14-16]. It is desirable for a
glass host to have a ΔT as large as possible. ΔT here is
113˚C (ΔT = Tx – Tg = 385 – 272 = 113˚C), indicating
that the SWL glasses have fairly good thermal stability
and are capable for further performing fabrication and
crystal- ree fiber drawing.
Table 1. The composition of Er3+ doped Sb2O3-Li2O-WO3
glasses and Er3+/Yb3+ codoped Sb2O3-Li2O-WO3 glasses
( mo l%).
No.
Sb2O3
WO3
Li O
Er2O3
Yb2O3
1
80
10
10
0.25
-
2
80
10
10
0.50
-
3
80
10
10
0.75
-
4
80
10
10
1.00
-
5
80
10
10
0.25
0.25
6
80
10
10
0.25
0.50
7
80
10
10
0.25
0.75
8
80
10
10
0.25
1.00
Figure 1. The DTA spectra of 0.25Er3+/0.75Yb3+ codoped
Sb2O3-Li2O-WO3 glas ses (mo l% ).
3.2. Absorption Spectra
Figure 2 showed IR spectra of 0.25Er3+/0.25Yb3+ and
0.25Er3+/0.75Yb3+ co-doped SWL glasses. The absorp-
tion band near 947 and 697 cm-1 is attributed to the vi-
bration of W-O and W -O-W respectively. The absorption
band near 600 cm-1 is attributed to symmetric bending
vibrations of Sb –O–Sb and the absorption band near 480
cm-1 is attributed to doubly degenerate bending vibra-
tions of [SbO3] structural units. In the glasses, Sb3+ ions
form a threefold coordination environment with oxygen
and Sb3+ behaves as a classic network-forming cation in
oxide glasses, creating a continuous random network of
Sb–O–Sb. The position of the highest phonon band is
important because the multi-phonon decay of rare-earth
ions in a glass depends on the maximum phonon energy
of the host glass [17,18]. In this kind of antimonate
glasse s, the highest band (600 cm-1) could be attributed to
the vibration of W-O. The maximum phonon energy of
the glass is low [10,19]. Therefore, it can be expected
that Sb2O3-WO3-Li2O glasses are good candidates for
fabrication of upconversion optical devices.
The absorption spectra of the Er3+/Yb3+ co-doped an-
timonate bulk glass in the visible region was shown in
Figure 3. Four absorption bands are shown by the ex-
cited levels, which are attributed to the transitions from
the ground state (4I15/2) to the excited state of Er3+ ions:
4F7/2, 2H11/2, 4F9/2 and 4I11/2 respectively [20]. T he absorp-
tion at the wavelength region at 980 nm is due to the
large contribution of the absorption of Yb3+, which arise s
from the 2F7/2→2F5/ 2 transition. Upon the introduction of
Yb3+ ions to Er3+ doped antimonate glasses, the absorp-
tion efficiency at about 980 nm bands is enhanced by
energy transfer process Er3+: 4I 15/2 + Yb3+: 2F5/2 → Er3+:

Upconversion Luminescence of Er3+/Yb3+ Co-Doped Sb2O3-WO3-Li2O Antimonate Glasses
36
Figure 2. IR spectra of the 0.25Er3+/Yb3+ codoped Sb2O3-
Li2O-WO3 glasses ( mol%).
Figure 3. The adsorption spectra of Er3+/Yb3+ codoped
Sb2O3-Li2O-WO3 glas ses.
4I11/2 +Yb 3+: 2F7/2. The results at this co ndition will make
more Er3+ io ns involving the pumped process [21,22].
3.3. Upconversion Fluorescence Spectra
Figure 4 illustra ted the upconversion emission spectra of
the 0.25 mol% Er3+, 0.5 mol% Er3+, 0.75 mol% Er3+ and
1.00 mol % Er3+ single doped SWL glasses in the wave-
length range of 500 - 700 nm with 980 nm LD under the
same powder 1062.6 mW excitation. The observed up-
conversion luminescence in the green spectral bands has
three humped peaks at 524, 544 and 656 nm wavelength
are attrib uted to the Er 3+: 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and
4F9/2 → 4I15/2 transitions respectively. The intens ity gain
increases with the increasing of Er3+ concentration from
0.25mol% to 0.75mol%, while decrease significantly
when the Er3+ concentration reaches 1.00 mol% due to
upconversion fluorescence que nching of Er3+ ions.
The upconversion emission spectra of 0.75 mol% Er3+
Figure 4. The upconversion emission spectra of the (a) 0.25
mol% Er3+, (b) 0.5 mol% Er3+, (c) 0.75 mol% Er3+ and (d)
1.00 mol% Er3+ doped Sb2O3-Li2O-WO3 glasses in the wa-
velength range of 500 - 700 nm with 980 nm LD under the
same powder 1062.6 mW (CI: 20 mA).
dop ed SW L glasse s in t he wavele ngt h range of 500 - 700
nm with 980 nm LD under different powder are shown in
Figure 5. T he LD cur r ent inte nsit y (CI) is varied from 10
mA to 20 mA every 2 mA, the corresponding power is
372.6 mW, 510.6 mW, 648.6 mW, 786.6 mW, 924.6
mW and 1062.6 mW.
Figure 6 shows the log-log dependences of the inte-
grated green (524 and 544 nm) intensities on the excita-
tion power at 980 nm. In frequency upconversion
process, the upconversion emission intensity Iup in-
creases in proportion to the input power of infrared (IR)
excitation inte nsity IIR, that is, Iup ∝ IIR n, wher e n is
the number of IR photons absorbed per visible photon
emitted. A plot of log Iup vs. log IIR yields a straight line
with slope n. The quadratic dependence indicates that
two photons are involved for the upconversion process.
The upconversion emission spectra of Sb2O3-WO3-
Li2O bulk glasses and the 0.25 mol % Er3+/0.25 mol%
Yb3+, 0.25 mol % Er3+/0.5 mol% Yb3+, 0.25 mol% Er3+
/0.75 mol% Yb3+ and 0.25 mol% Er3+/1.00 mol% Yb3 +
co-doped Sb2O3-Li2O-WO3 glasses in the wavelength
range of 500 - 700 nm with 980 nm LD under the same
powder 1062.6 mW were shown in Figure 7. Figure 8
showed the log dependences of the integrated green (5 24
and 544 nm) intensities on the amount of Yb3+ ions.
From the Figure 8, it can be seen that the addition of
small amount of Yb3+ ions to the glass containing Er3+
enhances the emission intensity of Er3+ ions 3 - 5 times
for 524 and 544 nm bands respective ly and sub sequently
the fluorescence intensity of Er3+ ions.
3.4. Upconversion Mechanisms Analysis
Based on the Figures 4-8 and according to the precious

Upconversion Luminescence of Er3+/Yb3+ Co-Doped Sb2O3-WO3-Li2O Antimonate Glass es
37
Figure 5. The upconversion emission spectra of 0.75 mol%
Er3+ doped Sb2O3-Li2O-WO3 glasses in the wavelength
range of 500 - 700 nm with 980 nm LD.
Figure 6. The log–log dependences of the integrated green
(524 and 544 nm) intensities on the excitation power at 980
nm.
reports, the mechanisms of energy transfer from Yb3+ to
Er3+ can be described as Figure 9. For the green emis-
sion, in the first step, the 4I15/2 level is directly excited
with 980 nm light as follows:
( )( )
434 3
15/2 11/2
F Er.HEra hpoton
++
+→
(1)
( )( )
23 23
7/2 5/2
FYb.F Yba hpoton
++
+→
(2)
An incident 980 nm photon is strongly absorbed by Yb3+
ions and excites them to 2F5/2 level along with the direct
absorption of Er3+ ions. The excited Yb3+ ions transfer
their excitation energy to unexcited Er3+ ions, promoting
them to 4I11/2 level thus enhancing the poplation of 4I11/2
level further [23,24]. Thus, the second step involves as
follows:
( )( )
4 343
11/2 7/2
IEr.F Era hpoton
++
+→
(3)
Figure 7. The upconversion emission spectra of (a) 0.25
mol% Er3+ and (b) 0.25 mol% Er3+/0.25 mol% Yb3+, (c) 0.25
mol% Er3+/0.5 mol% Yb3+, (d) 0.25 mol% Er3+/0.75 mol%
Yb3+ and (e) 0.25 mol% Er3+/1.00 mol% Yb3+ codoped Sb2O3-
Li2O-WO3 glasses in the w avelength range of 500 - 700 nm
wit h 98 0 nm LD under th e same pow der 1 062 .6 mW (CI: 20
mA ).
Figure 8 . The depende nces of the i ntegrated gree n (524 and
544 nm) intensities on the amount of Yb3+ ions.
Figure 9. Energy level diagram of Er3+/Yb3+ and upconver-
sion mechanis ms of Sb2O3-Li2O-WO3 glasses under 980 nm
exci tation power.

Upconversion Luminescence of Er3+/Yb3+ Co-Doped Sb2O3-WO3-Li2O Antimonate Glasses
38
()( )()( )
2343 2343
5/2 11/27/27/2
FYbIErF YbF Er
+ +++
+→ +
(4)
The populated 4F7/2 level of Er3+ then relaxes rapidly
and non-radiatively to the next lower levels, 2H11/2 and
4S3/2. The above processes then produce the two transi-
tions 2H11/2-4I15/2 and 4S3/2-4I15/2, which are centered at
524 and 544 nm respectively. The trace presence of Yb3+
ions provides an additional channel to populate Er3+ ion
levels, make more Er3+ ions involving the pumped
process and thus enhance the green fluoroscence intensi-
t y.
For the red emission, it can be seen from Figure s 4, 5
and 7, the upconversio n luminescence in the red spectral
bands at 650 - 670 nm wavelength is very weak, which
means few Er3+ ion s i s involving the following processes:
( )( )
4 343
11/2 7/2
IEr.F Era hpoton
++
+→
(5)
( )( )
4 343
11/2 13/2
I ErIEr.a hpoton
++
→+
(6)
( )( )
4 343
13/2 9/2
IEr.F Era hpoton
++
+→
(7)
4. Conclusions
A serie s of Er3+/ Yb3+ co-doped Sb2O3-WO3-Li2O glasses were
prepared. Intense green upconversion fluorescence was
observed near 524 and 544 nm i n t he Er 3+/Yb3+ co-doped
Sb2O3-WO3-Li2O glasses under 980 nm excitation. The
upconversion processes were proved to involve the se-
quential two-photon absorption process for the green
emissions. The maximum phonon energy of the glass is
about 348 cm-1, which is much lower than silicate
glasses. Upon the introduction of Yb3+ ions to Er3+ doped
antimonate glasses, the upconversion fluorescence effi-
ciency is enhanced by increasing of Yb3+ concentration.
The upconversion excitation increased with the increas-
ing o f LD p owde r. T he d ata presente d in t hi s wor k mig ht
provide useful information for further development of
Er3+-doped materials for upconversion optical devices.
5. Acknowledgements
This study was supported by Shanghai Leading Aca-
demic Discipline Project (B502) and Shanghai Key La-
boratory Project (08DZ2230500).
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