Individual mesoscopic structures studied with sub-micrometer optical detection techniques: CdSe nanocrystals capped with TOPO and ZnS-overcoated system

The synthesis of semiconductor nanocrystals (CdSe) by pyrolysis of organometallic reagents and their optical properties are reported. By controlling the relative amount of precursors to be injected into the coordinating solvent, e.g. TOPO, we have modified the sizes and quality of nanocrystals successfully, the spectrum of which shows fairly sharp excitonic spectral features even in a limited size range. Passivation with overcoating ZnS provides a large enhancement of the fluorescence intensity, i.e. quantum efficiency reaches over 50% at room temperature in the best case. To prepare nanocrystals larger than ∼4.0 nm, 2-step injection of CdSe precursors seems suitable, where some amount of TOPO is added separately to the reaction vessel prior to the secondary injection. With this additional process ZnS-overcoated CdSe nanocrystals of high quantum efficiency can be obtained with high reproducibility.