Photoluminescence dynamics of exciton-exciton scattering processes in CuI thin films

We have investigated the dynamical process of exciton-exciton scattering in CuI thin films grown on a (100) NaCl substrate under intense-excitation conditions. The time-integrated photoluminescence spectra clearly exhibit two photoluminescence bands which originate from the excitonic molecule and the inelastic scattering of excitons, so-called P emission. The time-resolved PL spectra obtained by using an optical Kerr gating method show that the peak energy of the P-emission band temporally changes in a picosecond region, which reflects the thermal distribution of excitons. In the time profile of the P-emission band, the rise time that is around 10.3em0exps becomes remarkably fast with increasing excitation power, while the decay time hardly depends on the excitation power. Moreover, we have found that the inverse of the rise time of the P emission exhibits an almost quadratic dependence for the excitation power. This finding suggests that the inverse of the rise time corresponds to the rate of the exciton-exciton scattering.