Abstract
Colloidal CdSe/ZnS core/shell quantum dots (QDs) can be used to generate single photons at room temperature for promising applications in quantum information sciences. Despite the existence of biexciton (BX) states, they would undergo fast nonradiative Auger relaxation (AR), leading to pure single-exciton (SX) emission, even under high-power excitation. In this work, the fluorescence properties of single colloidal QDs deposited on the conductive ITO surface have been investigated by combining photon correlation spectroscopy and time-tagged, time-correlated single-photon counting (TT-TCSPC) measurement. The conductive materials can introduce extra nonradiative (NR) processes, and thus can significantly alter pristine emission properties, including emission brightness, fluorescence lifetime, and photon emission statistics. We found that such a NR process can strongly quench SX emission but has less effect on BX emission, leading to the increase of the quantum-yield (QY) ratio between BX and SX emission. As a result, the purity of single-photon emission would be degraded despite the fact that fluorescence blinking can be suppressed. This experimental understanding is significant for further designing high-performance single-photon sources based on low-cost colloidal QDs operating at room temperature. © 2014 American Chemical Society.