Stoichiometric Ratio Dependent Photoluminescence Quantum Yields of the Thiol Capping CdTe Nanocrystals

Thioglycolic acid capping CdTe nanocrystals were synthesized under different stoichiometric ratios of Cd to Te precursors in aqueous solution. It was found that the photoluminescence quantum yield (QY) of the nanocrystals increased from 10.3 to 34.0% as the stiochiometric ratio of Cd to Te precursors used increased from 1.5:1 to 5.0:1. It is identified that the stoichiometric ratio of S to Te on the nanocrystal surface increased with increased initial stoichiometric ratio of Cd to Te precursors used in the syntheses, allowing the construction of more perfect surface under higher S/Te ratio. Time-resolved luminescence decay curves indicate there are two different decay lifetimes, corresponding to the intrinsic recombination of populated core states and the surface-related luminescence respectively. The surface-related luminescence is mainly responsible for the increased QY of the nanocrystals.