Temperature dependence of dynamical processes of photoluminescence from exciton–exciton scattering in CuI thin films

We have investigated the time-resolved photoluminescence spectra of the P emission due to exciton–exciton scattering in CuI thin films at various temperatures by using an optical-Kerr-gating method with a time resolution of 0.4 ps. It is found that the rise time of the P emission hardly changes with temperature. Since the rise time reflects collision processes of excitons in the lowest image exciton state, the temperature dependence demonstrates that the exciton–collision rate is hardly influenced by temperature. On the other hand, the decay time of the P emission becomes faster from 8 to 5 ps with increasing temperature from 10 to 150 K. This is due to the enhancement of the contribution of the photon state away from the polariton-bottleneck region to the photon-like polariton state leading to the P emission owing to thermal broadening in momentum space; namely the photon nature of the photon-like polariton becomes considerable.