Synthesis and characterization of II-VI and IV-VI colloidal semiconductor quantum dots

The synthesis and optical characterization of colloidal CdSe core and CdSe/ZnS core/shell quantum dots (QDs) is presented in this thesis. Scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) was used to determine the chemical distribution of semiconductor shell material around colloidal core-shell CdSe/ZnS QDs. Our studies have shown that although growth of a simple shell of ZnS on the surface of a CdSe core QD does improve the optical properties considerably, EELS signals from positions around the QD indicate a well-defined shell of ZnS surrounding the CdSe core, but the distribution of the shell material is highly anisotropic.;We have reported the formation of magic sized PbSe nanoclusters (MSCs) together with regular sized PbSe QDs. A method of preparing pure PbSe MSCs at low reaction temperature under ambient conditions is also presented. In comparison to other semiconductor QDs, these small sized MSCs show high fluorescence efficiency. The optical properties of PbSe MSCs provides them with enormous potential as superior fluorophores for biological imaging applications at NIR wavelengths between 700 and 1000 nm.;We also report the two-stage preparation of core/shell PbSe/SrSe colloidal quantum dots (QDs) and their characterization. Absorption, photoluminescence (PL), and energy dispersive X-ray spectroscopies (EDX) were used to characterize the QDs. In addition to the high quantum efficiency of the PbSe/SrSe core/shell QDs and the strong EDX Sr signals, these core/shell samples show a significant blue shift in their PL spectra when compared to PbSe QD cores. Further studies on the etching of PbSe core QDs were performed to determine the effect of oleic acid, octadecene, trioctylphosphine, and oxygen on the PL blue shifts.;Forster resonance energy transfer between different sized PbSe-PbSe QDs and PbS-PbSe QDs were observed. Different energy transfer efficency was obtained by studying PL spectra of mixed PbS/PbSe QDs in spun coated films. We have also studied energy transfer between semiconductor QDs placed in a Fabry-Perot microcavity. The spectrally integrated fluorescence from a monolayer of single sized QDs in the cavity is enhanced by a factor of 4.8 compared to free space. For a monolayer of mixed sized QDs, the acceptor QD fluorescence intensity is enhanced by an additional factor of 2.7 due to energy transfer processes. When the cavity mode is resonant with the acceptor QD fluorescence emission maximum, donor QD emission is completely suppressed, providing a narrow spectral output.