Time-resolved luminescence study on relaxation dynamics and morphology of self-trapped excitons in ionic crystals

Time-resolved spectroscopic studies on the intrinsic luminescence in alkali halides have revealed that there exist multiple local minima on the adiabatic potential energy surface (APES) for the self-trapped exciton (STE) state. These results are briefly reviewed, and closely connected subjects on the shape of the APESs for the lowest singlet-triplet STE pair, the electron-hole exchange energy, relaxation dynamics and the structure of STEs are discussed in terms of adiabatic instability during exciton self-trapping. A simple phenomenological model is proposed for the relaxation dynamics into on-center and off-center STE states, where an importance of the electron-hole spin correlation is pointed out.