Adiabatic Instability of the Self-Trapped Exciton in Alkali Halide Crystals

The adiabatic instability of the self-trapped exciton in alkali halide, as originally proposed by Toyozawa in 1978, has recently been shown to be not only very strong, but also quite general in alkali halides and alkaline earth fluorides. A number of properties of the off-center self-trapped exciton are presented here. These include a realistic re-evaluation of the pseudo Jahn-Teller hamiltonian parameters, the electric field gradient on the off-center V k core, and the volume change induced by the self-trapped exciton and ( F - H ) pairs of varying separation.