A STUDY OF ULTRAFAST SELF-TRAPPING PROCESSES OF ELECTRON-HOLE PAIRS IN RBI BY FEMTOSECOND PUMP AND PROBE SPECTROSCOPY

Initial formation processes of self-trapped excitons from free electro n-hole pairs in RbI crystals have been investigated by means of a femt osecond pump and probe spectroscopy. The short-lived intermediate anal ogous to the one-center self-trapped hole (STH) has been observed as a precursor for the self-trapped exciton (STE) in the time region of 0. 3-5 ps. The formation process of the STE in RbI is found to be quite s imilar to that observed in KI rather than KBr. From the observation of the two types of formation process depending on the species of haloge n atom, it is found that the lattice relaxation leading to the STE for mation is affected by the width of the valence band which consists of p-orbitals of halogen ions.