Charge-tunable optical properties in colloidal semiconductor nanocrystals

The optical properties of colloidal semiconductor nanocrystals are found to be extremely sensitive to excess electrons. Electrons in the lowest quantum-confined state of the conduction band of CdSe and (CdSe)ZnS nanocrystals quench photoluminescence by several orders of magnitude, at the same time, leading to a strong, mid-infrared intraband absorption and bleaching of the interband exciton transitions. Surface electrons are also efficient in quenching photoluminescence, but a passivating layer of wider band gap ZnS can reduce their influence. The results suggest that single-electron switching of photoluminescence may be feasible with improved core/shell structures of semiconductor nanocrystals.