IOP PUBLISHING
JOURNAL OF PHYSICS D: APPLIED PHYSICS
J. Phys. D: Appl. Phys. 41 (2008) 015404 (4pp)
doi:10.1088/0022-3727/41/1/015404
Spectroscopic properties of new
BaCl2–BaO–TeO2 tellurite glasses for
fibre and integrated optics applications
V G Plotnichenko1 , V V Koltashev1 , V O Sokolov1 , N V Popova1 ,
I A Grishin2 and M F Churbanov2
1
Fibre Optics Research Centre, Russian Academy of Sciences, 38 Vavilov Street, Moscow, 119333
Russia
2
Institute of Chemistry of High-Purity Substances, Russian Academy of Sciences, 49 Tropinin Street,
Nizhny Novgorod, 603600 Russia
E-mail: [email protected]
Received 4 September 2007, in final form 22 October 2007
Published 19 December 2007
Online at stacks.iop.org/JPhysD/41/015404
Abstract
We present results of the study of transmittance and Raman spectra in BaCl2 –BaO–TeO2
glasses possessing intense spontaneous Raman scattering which are promising for the
development of integrated and fibre stimulated Raman lasers. Compared with oxide–tellurite
systems these glasses are found to be transparent in a wider wavelength range, from 350 nm to
6.5 µm. A band near 765 cm−1 is found to arise in the Raman spectra of the glasses with total
BaO and BaCl2 content exceeding 30 mol%. The band turns out to be 70–80 times as intense
as the main Raman band with maximum near 440 cm−1 in SiO2 glass. Quantum-chemical
calculations of the structure and vibrational spectra of the glasses show that the 765 cm−1 band
is caused mainly by vibrations of O3 Te–O− and O2 Te=O non-bridging oxygen atoms.
(Some figures in this article are in colour only in the electronic version)
tellurite glasses with intensive Raman scattering with the
special attention given to oxyhalide tellurite glasses known
to exhibit the interval between crystallization and vitrification
temperatures considerably large compared with oxide tellurite
glasses [8].
So far, ZnCl2 (F2 )–ZnO–TeO2 [8–11] and LiCl–Li2 O–
TeO2 [8,12] oxyhalide tellurite glasses are the most extensively
studied systems. No publications concerned with the study of
BaCl2 –BaO–TeO2 glasses have come to our notice, though
there are numerous papers devoted to BaO–TeO2 [8, 13–16],
BaCl2 –TeO2 [8, 17] and BaF2 –TeO2 [8, 18] binary glasses.
1. Introduction
This paper is concerned with a search for and study of
new tellurite glasses for various nonlinear optical systems in
bulk, planar and fibre forms. Stimulated Raman scattering
amplifiers are considered to be one of the most promising
applications of tellurite glasses [1, 2] due to wide vibrational
spectrum and intense spontaneous Raman scattering of the
latter. Though Raman scattering in tellurite glasses has been
studied for more than 40 years, there are few works [3–7]
where absolute Raman intensities are measured (usually in
comparison with Raman spectrum of silica glass as reference).
Results of the measurement of absolute Raman scattering
intensity in ZnO–TeO2 , WO3 –TeO2 and MoO3 –TeO2 binary
tellurite glasses were presented in our paper [7]. We found
the intensity of certain Raman bands in these glasses to be
55–90 times as high as the intensity of the main 440 cm−1
Raman band in silica glass. However, binary glasses are of
limited use as materials for low-loss optical fibres. Thus
one should look for new, more complex compositions of
0022-3727/08/015404+04$30.00
2. Experimental
We prepared BaCl2 –BaO–TeO2 glasses by a conventional
technique of melting oxide and chloride reagents in ceramic
or platinum crucibles. Synthesis time and temperature ranged
from 15 min to 20 min and from 700 ◦ C to 800 ◦ C, respectively,
depending on the composition of the mixture. The samples for
measuring were 1 mm thick polished plates cut from annealed
1
© 2008 IOP Publishing Ltd
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J. Phys. D: Appl. Phys. 41 (2008) 015404
V G Plotnichenko et al
Table 1. Composition of the glass samples (in mol%).
Sample No
Mix composition
Results of x-ray analysis
1
2
3
4
5
6
7
8
9
10BaCl2 –10BaO–80TeO2
15BaCl2 –15BaO–70TeO2
15BaCl2 –25BaO–60TeO2
20BaCl2 –20BaO–60TeO2
37BaCl2 –18BaO–45TeO2
40BaCl2 –18BaO–42TeO2
30BaCl2 –30BaO–40TeO2
20BaO–80TeO2
20BaCl2 –80TeO2
8.7BaCl2 –10.0BaO–81.3TeO2
15.0BaCl2 –12.6BaO–72.4TeO2
14.7BaCl2 –22.4BaO–62.9TeO2
20.4BaCl2 –17.4BaO–62.2TeO2
33.4BaCl2 –18.9BaO–47.7TeO2
32.2BaCl2 –19.2BaO–48.6TeO2
33.7BaCl2 –26.0BaO–40.3TeO2
17.2BaO–82.8TeO2
19.2BaCl2 –80.8TeO2
80
70
7
70
9
9
5
50
4
3
2
1
50
40
30
20
19.9 ZnO – 80.1 TeO2
40
30
8
20
19.6 MoO3 – 80.4 TeO2
19.6 MoO3 – 80.4 TeO2
19.9 ZnO – 80.1 TeO2
350
400
450
500
Wavelength (nm)
18.9 WO3 – 81.1 TeO2
10
18.9 WO3 – 81.1 TeO2
10
0
5
60
Transmission (%)
Transmission (%)
60
8
0
5
550
6
7
8
Wavelength (µm)
9
10
11
Figure 2. Tellurite glasses transmission near the long-wavelength
edge.
Figure 1. Tellurite glasses transmission near the short-wavelength
edge.
460
Short-wavelength absorption edge (nm)
bulk glass. The composition of the samples was analysed on a
JEOL x-ray microanalyser by scanning of the sample surface
within ∼1 mm2 area. The composition of the mixtures and of
the glass samples are given in table 1.
The transmission spectra of the samples were measured on
a Lambda 900 spectrometer in the 0.30–2.50 µm wavelength
range and on an IFS-113v Fourier spectrometer in the 2–10 µm
range. Raman spectra were measured on a triple T-64000
spectrograph in 90◦ -scattering configuration. A Stabilite 2017
argon laser at 514.5 nm was used as an incident light source.
The measured spectra were reduced multiplying them by
(1 + nb )−1 ω−4 factor with nb = [exp(h̄/kT ) − 1]−1 being
the Bose distribution function, ω being the scattered light
frequency, being the Stokes shift, and by a factor taking
into account changes of scattering geometry and light intensity
caused by reflections and refraction at sample surfaces (see
[3, 4, 7] for further details). The reduced spectra were
normalized to the main band (∼440 cm−1 ) intensity of the
reduced Raman spectrum of SiO2 glass measured on the same
setup and in the same conditions as for the tellurite glasses.
BaCl2– BaO–TeO2
19.2 BaCl2– 80.8 TeO2
440
17.2 BaO – 82.8 TeO2
19.9 ZnO – 80.1 TeO2
18.9 WO3– 81.1 TeO2
420
400
380
360
0
5
10
15
20
25
30
35
BaCl2 concentration (mol.%)
Figure 3. Dependence of the short-wavelength transmission edge of
BaCl2 –BaO–TeO2 glasses on BaCl2 content.
numbers at the curves in the figures correspond to glass
compositions listed in table 1).
The short-wavelength transmission edge is displaced
towards higher frequencies with BaCl2 added in binary BaO–
TeO2 composition (figure 1). Depending on the glass
composition the short-wavelength edge measured at the 10%
level for 1 mm thick glass samples is found to be shifted from
402 nm for 17.2BaO–82.8TeO2 glass to 401 nm for 8.7BaCl2 –
10.0BaO–81.3TeO2 glass and to 368 nm for the 33.4BaCl2 –
18.9BaO–47.7TeO2 one. As is evident from figure 3, this
shift grows practically linearly with the BaCl2 content in glass.
3. Results and discussion
The transmission spectra of BaCl2 –BaO–TeO2 glasses are
shown in figures 1 (the short-wavelength transmission edge)
and in 2 (the long-wavelength edge) in comparison with those
of some most frequently studied binary tellurite glasses (the
2
J. Phys. D: Appl. Phys. 41 (2008) 015404
V G Plotnichenko et al
SiO2 -normalized Raman intensity
80
70
60
1
50
2
Te
3
40
Te
O
4
30
5
Te
20
10
Ba
O
O
Cl
Te
SiO2 (× 10)
O
0
0
100
200
300
400
500
600
Raman shift (cm-1)
700
800
900
Te
Figure 4. Raman spectra of BaCl2 –BaO–TeO2 glasses.
90
SiO2 -normalized Raman intensity
80
70
Figure 6. Fragment of BaCl2 –BaO–TeO2 glass network: calculated
atomic arrangement.
5
glasses and calculated the intensity of Raman scattering in
characteristic structural groups. The equilibrium configuration
of tellurite glass network fragments containing barium and
chlorine atoms was calculated by ab initio Car–Parrinello
molecular dynamics using the Quantum-ESPRESSO package
[19] (figure 6). The calculation shows that these atoms
occur in the glass network as Ba2+ and Cl− ions forming
no covalent bonds with neighbouring atoms and giving rise
to negatively charged O3 Te–O− groups (fourfold coordinated
tellurium atom with non-bridging oxygen atom) and neutral
O2 Te=O groups (threefold coordinated tellurium atom with
non-bridging oxygen atom). The amount of these groups is
determined by barium and chlorine atoms content in glass.
On average, two O3 Te–O− groups and two or three O2 Te=O
groups per BaO group and three O2 Te=O per BaCl2 group
are formed. Two such O3 Te–O− groups (Te–O− bond shown
by thin lines) and two O2 Te=O ones (Te=O bond shown by
thick lines) are seen in figure 6. Non-bridging oxygen atoms
are shown in figure 6 by thick circles. Thus, according to our
calculation a network of BaCl2 –BaO–TeO2 glasses is built of
structural groups of three types, TeO4 , O3 Te–O− and O2 Te=O.
This allows us to explain the characteristic changes of the
Raman spectrum with glass composition seen in figure 4 by a
change of ratio between the concentrations of these structural
groups.
The Raman band in the range 550–850 cm−1 turns out to
be complex. It is formed mainly by four components, namely
645 cm−1 (antisymmetric stretching of Te–O bonds in Te–O–
Te linkages between TeO4 groups), 765 cm−1 (Te=O double
bonds in O2 Te=O groups), 775 cm−1 (Te–O− bonds in the
O3 Te–O− groups with non-bridging oxygen atoms being on
the long Te–O bonds), and 800 cm−1 (Te–O− bonds in the
O3 Te–O− groups with non-bridging oxygen atoms being on
short Te–O bonds). With the ratio between concentrations
of the structural groups varying, the shape of the complex
band can change from bell-shaped for glass composition
close to xBaCl2 –xBaO–(1 − 2x)TeO2 with x 0.15 to
nearly triangular with maximum at about 765 cm−1 for glass
60
18.9 WO 3 – 81.1 TeO2
50
40
21.4ZnO – 79.6TeO2
30
20
SiO2 (× 10)
10
0
0
100
200
300
400
500
600
700
800
900
1000
Raman shift (cm-1)
Figure 5. Comparison of Raman spectra of several tellurite glasses.
On the other hand, BaCl2 –BaO–TeO2 glasses are considerably
more transparent in the middle IR range in comparison with
binary oxide–tellurite glasses (figure 2). Hence the total
transparency range of oxychloride tellurite glasses turns out
to be much wider in comparison with oxide ones.
Raman spectra of several BaCl2 –BaO–TeO2 glasses
reduced as explained above are shown in figure 4. Significant
growth of a narrow (HWHF 50 cm−1 ) band near 765 cm−1
is observed in the spectra for BaO and BaCl2 total content
>30 mol.%. The maximal intensity of the band turns out
to be 75 times as high an intensity of the 440 cm−1 band in
silica glass which is chosen as a reference band with Raman
intensity taken to be unity. For comparison, the absolute
values of Raman spectra of 21.4ZnO–TeO2 and 81.1TeO2 –
18.9WO3 glasses are shown in figure 5 together with that
of the 33.4BaCl2 –18.9BaO–47.7TeO2 one. The maximal
intensities in these spectra are ∼55, 85 and 75, respectively.
As evident from figure 4, it is possible, if required, to
choose BaCl2 –BaO–TeO2 glass composition with both the
main tellurite band near 645 cm−1 and the band near 765 cm−1
being approximately identical in intensity (∼50) with total
width of about 200 cm−1 .
To understand the origin of the main bands in Raman
spectra of BaCl2 –BaO–TeO2 glasses we performed quantumchemical modelling of the network structure of such
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J. Phys. D: Appl. Phys. 41 (2008) 015404
V G Plotnichenko et al
composition of the 3xBaCl2 –2xBaO–(1 − 5x)TeO2 kind with
x ≈ 0.1.
There is a relatively weak and wide band near 150 cm−1
in the Raman spectra of BaCl2 –TeO2 glasses (figure 4). Our
calculation allows us to conclude that this band is caused by
vibrations of O3 Te–O− groups in vicinity of Ba2+ ions. Such
a vibration includes rocking of the non-bridging oxygen atom
together with bending of neighbouring Te–O–Te linkages. The
Raman feature near 150 cm−1 resembles one near 235 cm−1
known in ZnCl2 –TeO2 glasses (see e.g. [10]). The 235 cm−1
feature is ascribed in [10] to the mutual vibrational motion of
Zn and O and (or) Zn and Cl atoms. Our calculations of ZnCl2 –
ZnO–TeO2 glasses (to be published elsewhere) are consistent
with such an assumption. So the Raman feature at 150 cm−1
in BaCl2 –TeO2 glasses and one at 235 cm−1 in ZnCl2 –TeO2
glasses seem to be of different origin.
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4. Conclusion
In conclusion, we have prepared and studied new
BaCl2 –BaO–TeO2 tellurite glasses. The transparency range
of these glasses is found to be considerably broader compared
with oxide tellurite glasses and the main Raman band of
BaCl2 –BaO–TeO2 glasses is proved to be only slightly less
intensive and narrower than that of WO3 –TeO2 glasses. By
varying the concentrations of BaO and BaCl2 one is able
to considerably change the shape of the main Raman band
with its intensity being approximately constant. Hence
BaCl2 –BaO–TeO2 glasses turn out to be promising materials
for Raman optical devices.
Acknowledgment
This work was supported by the Russian Foundation for Basic
Researches (grant No 06-02-16727a).
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