Absorption and Emission Spectra of Impurities in Solids

Abstract

Absorption and emission line shapes are calculated for impurities that couple to the lattice through an interaction containing both linear and quadratic terms. Specific examples of absorption-band shapes are computed for temperatures at and well above 0 K, and are compared to band shapes for the limiting cases of linear interaction and quadratic interaction. The strength of the quadratic-interaction parameter is shown to influence the shape, and thereby the observation, of zero-phonon lines; the temperature dependence of the over-all spectral-band shape; and the symmetry of the absorption and emission spectra. From the temperature dependence of the absorption-band shape observed experimentally, values of the linear- and quadratic-interaction parameters can be estimated.