Absolute Raman intensities in glasses II germania-based heavy metal oxides and global criteria.

The theoretical expressions for absolute Raman intensities derived in Part 1 have been generalized in two ways; one for application to multicomponent glasses and the other to enable qualitative global predictions to be made in terms of such fundamentals as valency, bond length and mass. From the latter it is anticipated that the most intense Raman spectra among good glass formers will most likely be found in multicomponent heavy metal oxide glasses. Using the full multicomponent theory, a detailed comparison is then made with experimental Raman spectra for ten different binary through quaternary germanate glasses containing Tl(2)O, PbO, Bi(2)O(3) and/or Sb(2)O(3). Adopting a simple model which is based on the assumption of a dominantly four-fold coordinated germanium site leads to estimates for the number of bridged-anion and non-bridged- anion modes which, when coupled with the theoretical intensity expressions of such components, explains in a surprisingly quantitative manner the measured intensities of the corresponding Raman spectral features. An equally detailed discussion is presented of the lowest frequency acoustic-Raman or 'boson' peak and absolute intensity predictions again compare well with experiment for all ten germanate compositions.