Dynamical process of exciton–exciton scattering in CuI thin films

We have investigated the time-resolved photoluminescence (PL) spectra of CuI thin films under intense excitation conditions in the time region up to 25 ps. In the time-integrated PL spectra, we have clearly observed the PL band originated from the inelastic scattering of excitons, so-called P emission. The time-resolved PL spectra obtained by using an optical Kerr gating method exhibit that the peak energy of the P-emission band temporally changes in a picosecond region, which reflects the variation of the effective temperature of excitonic system. In the time profile of the P-emission band, we found the following two characteristic properties. One is that the decay time hardly depends on the excitation power. The other is that the rise time becomes considerably faster with increasing excitation power. Moreover, we have found that the inverse of the rise time of the P emission exhibits an almost quadratic dependence on the excitation power.