A theoretical study of the pi -luminescence from self-trapped excitons in alkali halide crystals

Abstract

It is shown that the equilibrium axial shift of the Vk core of the self-trapped exciton (STE) in alkali halides is correlated with the lifetime and Stokes shift of the pi -emission band and the binding energy of the STE. A configuration coordinate diagram for the STE in KC is constructed which is consistent with existing data and accounts for the large Stokes shift and large binding energy of the STE. A detailed comparison is made between the configuration coordinate diagrams based on the off-centre (F-H pair) model and the on-centre (Vk+e) model of the STE. Using a previously developed extended-ion program package coupled with a CNDO code, the pi -emission band peak energies and the binding energies of the STE are calculated for 12 alkali halides. The results are in general agreement with experiment.