Luminescence-intensity kinetics due to nonradiative capture by multiphonon emission in highly excited CdS and CdSe crystals

The temporal kinetics of radiative recombination of a nonthermalized electron-hole plasma photoexcited by a powerful pulse of picosecond duration is considered with respect to the nonradiative capture of hot nonequilibrium carriers by deep centers via multiphonon emission (MPE). For centers thermally activated through surmounting the Localization barrier by the carrier-lattice system, a decrease of the luminescence rise time and an occurrence of the fast-relaxation stage are shown to be characteristic of the band-to-band emission evolution at elevated lattice temperatures. An effect of MPE capture on the luminescence kinetics is experimentally demonstrated in CdS crystals with different concentrations of excess cadmium, and in a high-purity CdSe crystal. The analysis of the kinetics revealed deep traps, probably of native origin, with localization barriers of 110 meV for CdS and 215 meV for CdSe.