Exciton-polariton bottleneck and the thermalization of polariton luminescence in CdS and CdSe

Abstract

The decay in time of polariton luminescence (PL) excited by picosecond laser pulses in CdS and CdSe has been studied both experimentally and theoretically. The time dependence of the PL is measured with a time-resolved photon counting system with subnanosecond resolution. The decays of the PL are found to be approximately single exponentials at low ( K) and high (>20 K) temperatures. At intermediate temperatures the decays are better approximated by a sum of two exponentials. These experimental results are found to be well reproduced by theoretical calculations based on a two-branch polariton model. Pekar’s additional boundary condition is adopted in calculating the time-resolved PL spectra. A comparison between theory and experiment enabled the polariton bottleneck to be identified. Furthermore, it is shown that at finite temperatures the polariton bottleneck enables a quasithermal equilibrium to be established among polaritons.