Spontaneous and stimulated collapse of high density electron-hole system in CdSe

The change of the delay of stimulated emission was observed in the platelets of CdSe ( 80K ) in the case of interband excitation by picosecond laser pulses. The delay increased from 30 ps at high to 0, 6-1 ns at relatively low pumping intensities probably indicating the replacement of stimulated emission of electron-hole plasma by stimulated emission of high density excitons. While the spectra of luminescence from the irradiated volume remained almost unchanged at different pumping intensities the abrupt change of the delay allowed to distinguish at least these two radiative recombination processes.