Dynamical Aspects of Self-Trapping of 1s Excitons in RbI and KI

Abstract

Previously direct measurements of the self-trapping time of 1s excitons in KI was reported. In this paper, measurements for RbI are described. Picosecond pulses of the fifth harmonic (212.8 nm) of a Nd³⁺: YAG laser, which can directly generate the 1s excitons are used as the excitation source. The rise time of the E_x luminescence is measured at 4.2 K. From the observed rise time, the self-trapping time is estimated to be 2.0±0.5 ns. The height of the adiabatic potential barrier separating the free and self-trapped exciton states is measured to be 18 and 30 meV for RbI and KI, respectively. The self-trapping time and the barrier height in RbI and KI are compared, and their changes with changing material are discussed on the basis of the theoretical calculation.