Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 224
6.3.1. Infrared spectroscopy
6.31.1. Infrared spectroscopy of oxide tellurite glasses
Infrared spectroscopy of glasses of the series (80-x)TeO2-10Na2O-10ZnO-xMO, where
MO is PbO or GeO2
Fig. (6.6) shows infrared spectra of glasses in the series (80-x)TeO2-10Na2O-10ZnO-
xMO, where MO is PbO or GeO2, for MOD006 (x = 3 mol. % PbO), MOD010 (x = 5
mol. % PbO) and MOD012 (x = 5 mol. % GeO2). Fig. (6.7) shows the multiphonon edge
of these glasses. The 3 and 5 mol. % PbO glasses had approximately the same
multiphonon edge (the edge of the 3 mol. % glass was at a slightly higher wavenumber).
The edge for the GeO2 containing glass was found to be at a higher wavenumber than the
PbO glasses. This is probably due to a combination of: (i) Ge is of a lower atomic mass
than Pb, and (ii) the Pb-O bond (382.0 kJ.mol -1 ) is weaker than the Ge-O bond (659.4
kJ.mol -1 ) [6]. Applying the Szigeti equation (2.8), the multiphonon edge will tend to be
shifted to a higher wavenumber if GeO2 is substituted for PbO, as µ (reduced mass) will
decrease, and k (related to bond strength) will increase. The edge will also tend to shift to
higher wavenumbers from 5 to 3 mol. % PbO, as PbO was substituted for TeO2, and is
much heavier (Z = 82 and 52, respectively). Using the Szigeti equation (2.8), µ will
decrease with decreasing PbO content, which will tend to shift the multiphonon edge to
higher frequencies.