Synthesis, Characterization and Application of Luminescent Quantum Dots and Microcrystalline Phosphors
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Si QDs embedded in SiOx or SiNx thin films, which could emit light in the entire visible range from 440 nm to 840 nm by controlling their size and/or their matrix, were synthesized by evaporation or plasma enhanced chemical vapor deposition techniques. Various shades of white could be obtained from multi-layered SiNx film structures by controlling the size of Si QDs and layer thickness. It was shown that the combination of these films can produce white emission spectra with superior color rendering properties compared to conventional fluorescent tubes. Such Si-based QDs can be used as down-converting phosphors to coat a blue/UV LED to generate white light, providing a less expensive fabrication process to obtain advanced solid state lighting devices. As a supplement, free CdTe QDs with emission colors spanning 520~700 nm and quantum efficiency up to 54%, were synthesized using a colloidal chemical method for white LED applications. White PL and a range of emission colors were obtained from mixed CdTe QD samples excited by a 420 nm blue LED. Another part of this research was to develop a new x-ray powder phosphor, ZnTe:O, for biological imaging applications used in CCD-based synchrotron x-ray detectors. A unique dry synthesis process, including gaseous dry doping and etching procedures, was developed to synthesize ZnTe:O phosphors. The excellent x-ray luminescence results of oxygen doped ZnTe, including high efficiency, high resolution, fast decay, low afterglow and an improved spectral match to the CCD detector, indicated that ZnTe:O is a promising phosphor candidate for x-ray imaging applications.