Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 229
a change in the multiphonon edge. Tellurium also has a higher charge than zinc, therefore
also has a higher lattice energy. Using equation (2.8), addition of zinc will result in a
decrease in µ (reduced mass), causing the edge to shift to higher frequencies.
Fig. (6.13) shows the multiphonon edges of glass of composition 80TeO2-10Na2O-
20ZnO mol. % (MOD013) with thickness viz. 2.98, 0.50 and 0.20 mm. The multiphonon
edge was enhanced with decreasing thickness due to an increasing amount of signal
reaching the detector. Ernsberger [14] has shown that by using very thin silicate glass
samples it was possible to ‘extend the useful spectrum [of silicates] to ≈ 1,300cm -1 ’ i.e.
enable us to see more clearly bands that were indistinguishable before. This is also true
for tellurite glasses as fig. (6.14) and (6.15) show [5]. In the spectrum of thin (0.20 mm)
glass, of composition 80TeO2.10ZnO.10Na2O (mol. %), the higher wavenumber shoulder
of the 3060 cm -1 band can be more clearly discerned than in the spectra of the longer
optical pathlength specimens (fig. (6.15)), and at least four bands thought to be related to
structural units in the glass network (see below) can be seen within the multi-phonon
absorption edge (fig. (6.14)). Fig. (6.16) to (6.17) show the Gaussian deconvolution of
these OH bands in the longer optical pathlength samples.
Scholze [17] identified a band around 3500 cm -1 for alkali metal silicate glasses and
attributed this to the stretching mode of the free Si-OH groups. Ryskin [22, 23] also
identified a band around 3500 cm -1 for hydrated crystalline silicates and attributed this to
a stretching mode of the water molecule. It is therefore proposed that the band around
3300 cm -1 in fig. (6.17) (which is a shoulder of the 3060 cm -1 band) be attributed to free
Te-OH groups or molecular water (or a combination of both) [5]. By exposing thin glass
films to a high a vapour pressure of water (i.e. steam) Ernsberger [14] entrapped