Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 233
bands both result in active modes in the infrared. In reality it is not this simple, because
Raman and IR have different quantum mechanical selection rules (for IR, mode is only
active if incident radiation stimulates a change in dipole moment); however this serves as
a good first approximation [25].
Infrared spectroscopy of WO3 containing glasses
Fig. (6.19) shows infrared spectra of glasses MOD014 (90TeO2-5WO3-5Nb2O5 mol. %),
MOD015 (82.5TeO2-7.5WO3-10Nb2O5 mol. %), and MOD016 (70TeO2-25WO3-5Bi2O3
mol. %). The multiphonon edge shifted to higher wavenumbers and developed a shoulder
with increasing WO3 content. WO3 is highly refractory (TeO2 Tm = 733°C, WO3 Tm =
1473°C, and Nb2O5 Tm = 1460°C) and therefore has a much higher bond strength W-O
(672 kJ.mol -1 ) compared to Te-O (376.1 kJ.mol -1 ) [6]. Using the Szigeti equation (2.8),
substituting WO3 for TeO2 will increase k (the bond force constant), shifting the
multiphonon edge to higher frequencies.
A number of studies has been performed on the structure of tungsten-tellurite glass
systems [26-29]. The bands which developed, in the multiphonon edge, which increased
in intensity with increasing WO3 content, can be clearly seen in fig. (6.19) and (6.20).
This author would propose the band which occurred at around 1770 cm -1 (5.65 µm) can
be attributed to the first overtone of the asymmetric vibrations of the [WO6] octahedra (2
× 870 cm -1 = 1740 cm -1 ) [26, 28, 29]. This author would propose that the band which
occurred at around 1870 cm -1 (5.35 µm) can be attributed to the first overtone of the
symmetric vibrations of the [WO4] tetrahedra (2 × 930 cm -1 = 1860 cm -1 ) [26, 28, 29].