(CDSE)ZNS CORE-SHELL QUANTUM DOTS - SYNTHESIS AND CHARACTERIZATION OFA SIZE SERIES OF HIGHLY LUMINESCENT NANOCRYSTALLITES

We report a synthesis of highly luminescent (CdSe)ZnS composite quantu m dots with CdSe cores ranging in diameter from 23 to 55 Angstrom. The narrow photoluminescence (fwhm less than or equal to 40 nm) from thes e composite dots spans most of the visible spectrum from blue through red with quantum yields of 30-50% at room temperature. We characterize these materials using a range of optical and structural techniques. O ptical absorption and photoluminescence spectroscopies probe the effec t of ZnS passivation on the electronic structure of the dots. We use a combination of wavelength dispersive X-ray spectroscopy, X-ray photoe lectron spectroscopy, small and wide angle X-ray scattering, and trans mission electron microscopy to analyze the composite dots and determin e their chemical composition, average size, size distribution, shape, and internal structure. Using a simple effective mass theory, we model the energy shift for the first excited state for (CdSe)ZnS and (CdSe) CdS dots with varying shell thickness. Finally, we characterize the gr owth of ZnS on CdSe cores as locally epitaxial and determine how the s tructure of the ZnS shell influences the photoluminescence properties.