Time dynamics of free- and bound-exciton luminescence in CdSe under low- and high-intensity excitation.

A low-intensity direct measurement of the ${D}^{0}$X bound-exciton lifetime in CdSe is presented. A lifetime of 410 ps is measured, indicating a very large oscillator strength for this mostly radiative transition. The free-exciton lifetime is measured to be 1.4 ns, and is probably limited by trapping. At intensities of the order of 100 kW/${\mathrm{cm}}^{2}$, large changes of the time evolution of the luminescence intensity of both the free and bound excitons are observed. The bound-exciton luminescence appears almost instantaneously before decaying rapidly in the first 200 ps, and then the rate of decay slows considerably. This time behavior is believed to result from an interplay between stimulated emission and an induced absorption due to a self-broadening of free excitons at large densities.