Anti-Stokes photoluminescence and structural defects in CdSe/ZnSe nanostructures

An efficient anti-Stokes photoluminescence (ASPL) in multistacked CdSe/ZnSe nanostructures with quantum dots (QDs) has been found under the excitation below the QD ground states. An efficiency of ASPL is a few percents of the Stokes one. The dependencies of anti-Stokes emission spectra on temperature and excitation density have been studied. It is shown that excitation mechanism of this luminescence at low temperature can be explained by the two-step two-photon absorption process involving deep levels of cation vacancy related defects as intermediate states. It is found that with temperature increase resonant excitation in QD photoluminescence band may occur and contribution of thermal excitation of carriers becomes actual.