Moments of Impurity Absorption Bands in Solids

Abstract
It is shown that the contributions to the first three moments of an optical absorption (or emission) band of a point defect in a solid due to uncoupled lattice modes or perturbations are additive. Deviations from simple additivity may be caused by quadratic or higher cross terms in the interaction Hamiltonian or by deviations from adiabaticity. Difficulties and ambiguities in giving a consistent second‐order treatment for extracting coupling parameters from observed moments are pointed out.