Picosecond Spectroscopy of Excitonic Molecules in CuBr

Abstract

Time-dependence of the excitonic molecule luminescence in CuBr is measured at 4.2 K under the one-photon band-to-band excitation and the two-photon resonant excitation of excitonic molecules by using a picosecond tunable laser. The lifetimes of excitonic molecules and single excitons are determined to be 60 ps and 150 ps, respectively, by analyzing the results for the two cases of excitation. With these values of the lifetimes, the time-dependence of the luminescence under two types of excitation is explained self-consistently. The lifetime of molecules almost agrees with the radiative lifetime calculated by using existing theories. It is found that the probability of the formation of excitonic molecules per one collison of two single excitons is quite low, and that in the case of the resonant excitation the re-formation process of molecules is negligible.