De-excitation pathways of vibrationally excited excitons

Abstract

The de-excitation processes of the unstable exciton-phonon complex, generated by exciting the hole of the self-trapped exciton (STE) to energy levels much higher than the 1 s free exciton, have been studied in alkali halides. Three reaction channels have been investigated: (1) generation of free excitons, (2) Auger transitions to the electron-excited state of the STE, and (3) the reorientation of STE. Generation of free excitons occurs only for the hole excited to the π u orbital, wheras the Auger transition occurs at any hole-excited states with almost identical quantum yield. Reorientation of the molecular axis of the STE upon excitation to the σ g orbital occurs predominantly through 60° jumps. The quantum yield for these reactions is of the order 0.01, indicating that the dominant de-excitation channel is to restore the original lowest state of STE. Possible mechanisms explaining these results are discussed.