A model for the multi-exponential excited-state decay of CdSe nanocrystals

We report on photoluminescence decay measurements of CdSe nanoparticles over several decades of intensities and times, and as a function of size and temperature. A model is proposed for the multi-exponential decay kinetics, and their temperature dependence, in which a major role is played by the now well established presence of a large ground-state dipole moment in CdSe nano crystals. By two-photon excitation within the bandgap region we show that there is a link between the ground-state dipole moment and the excited-state decay. The stochastic nature of the magnitude of the dipole moment results in a complex temperature dependence. Contrary to studies that ascribe non-radiative decay processes to surface states/traps, the mechanism we propose considers the intrinsic states described within the effective mass approximation models for the spectroscopy of the bandgap. Surface effects are mediated by the ground-state dipole moments that they constitute, which in turn perturb the intrinsic states.