Free and self-trapped excitons in rare-gas cryocrystals: coexistence and mixing of states

Abstract

The absorption spectra for rare-gas cryocrystals are calculated taking into account one-phonon scattering and multiphonon interaction of free excitons with local lattice vibrations. The possibility of coexistence of free and self-trapped excitons in nonequilibrium states above the bottom of the exciton band is discussed on the basis of a comparison of the free exciton energy with exciton damping in the one-phonon scattering and during transitions to exciton-vibron states. It is found that free exciton damping at low temperatures is mainly determined by one-phonon scattering in the entire exciton band only for xenon. In argon and krypton crystals, both types of damping make comparable contributions. The probability of transition of an exciton to self-trapped states in neon is so high that the existence of band excitations is unlikely.