Raman Scattering by Color Centers

It is pointed out that the Raman spectrum of a color center gives significant information on the vibration spectrum associated with an electronic transition of the center itself. The formal theory of the first-order Raman scattering by substitutional defects in alkali halides is developed in detail. The coupling coefficients according to which the irreducible representations of the perturbed normal modes enter the total Raman spectrum are shown to be simply related to the stress coefficients of the absorption band. Calculations on the first-order Raman spectra of F centers in NaCl and KCl are found to be in fairly good agreement with experimental data recently obtained. An application of the present method to the theory of local-mode sidebands is also outlined.