Exciton relaxation processes in colloidal core/shell ZnSe/ZnS nanocrystals

Colloidal ZnSe nanocrystals are coated with a ZnS shell and are investigated by means of time-resolved photoluminescence spectroscopy. These nanocrystals are stable against photooxidation and have photoluminescence quantum efficiencies around 15% even months after the synthesis. Recombination processes are investigated as a function of the excitation intensity and the emission energy. Nonlinear processes such as Auger recombination dominate in the early times after the photogeneration of electron-hole pairs. The lifetime of single exciton states is shorter in smaller ZnSe dots than in larger ones, in accordance with theoretical predictions and as previously observed on similar systems.