Transitions from spontaneous emission to stimulated emission and superfluorescence of biexcitons confined in CuCl quantum dots

Time-resolved photoluminescence spectra of biexcitons in CuCl quantum dots embedded in NaCl matrix have been measured by two configurations of optical Kerr gate method. As for a backward configuration, a transition from spontaneous to stimulated emission is observed with increase in the excitation density. On the other hand, by a configuration collecting signals from the edge of the sample in the direction of the excitation length, an essential change in the time profile of biexciton luminescence from a conventionally exponential to a pulse-shaped according to the increasing excitation density reasonably suggests a shift from spontaneous emission to superfluorescence of biexciton luminescence.

► We perform two excitation configurations to examine transitions of emission from biexcitons confined in CuCl quantum dots. ► With the backward configuration, the pure lifetime of biexcitons is obtained due to an effective suppression of the reabsorption process. ► With the second configuration, the time profile of biexciton luminescence changes from conventionally exponential to pulse-like shape with the increasing excitation density. ► Change in the time profile cannot be explained qualitatively by an amplification process but by a transition to superfluorescence.