Quantum efficiency of stimulated emission in colloidal semiconductor nanocrystal quantum dots

External differential quantum efficiencies were studied for the stimulated emission of thin films of colloidal CdSe/CdS/ZnS nanocrystal quantum dots (NQDs) using the integrating sphere technique. A maximum efficiency of 34% was measured for the stimulated emission in NQDs which far exceeds that for spontaneous emission (9%). The competition between the radiative exciton/biexciton recombination and the carrier density-dependent nonradiative relaxation processes in NQDs was modeled to account for the observed difference in efficiency.