Raman scattering from impurities in nonmetals. I. Phonon effects

The influence on the impurity Raman spectrum owing to the variation of phonon frequencies with the occupancy of the impurity state is studied. For a Hamiltonian which simulates the situation of change in phonon frequencies, the Raman spectrum function, which yields information about the total scattered intensity per unit time per unit solid angle as well as the line shape, is expressed exactly as a triple integral. It is shown that when the impurity state interacts predominantly with a single phonon mode, a set of lines appear which are displaced at equal frequency interval from the (zero-phonon) Raman lines. Under the condition when they are unresolvable owing to instrumental width or when the impurity is coupled with the continuum phonon spectrum, these additional contributions asymmetrically broaden the zero-phonon Raman lines.