Synthesis And Applications Of Novel Ⅱ-Ⅵ Quantum Dots And Investigation Of Relative Mechanisms

Quantum dots (QDs) are novel inorganic semiconductor nanocrystal materials. The new core-shell aqueous quantum dots own good optical characters and high optical and chemical stability, can be used to biolabeling as the fluorescence probe and have many relative advantages compared with bare quantum dots synthesized in organic solvents. Doped quantum dots developed new views of scientists on synthetic chemistry because doped quantum dots have many advantages compared with undoped semiconductor quantum dots. It is very important to use green chemistry routes to realize industry production of doped quantum dots. This dissertation focus on synthesis of novel core-shell aqueous quantum dots, labeling in tumor cells—HeLa as the fluorescence probe, and synthesis and investigation of mechanisms of doped quantum dots (Mn:ZnSe and Mn:CdSe QDs). We also investigated the reaction conditions, relative mechanism and optimized experiment parameters of quantum dot growth and hope that this research is useful to the investigation of quantum dots in the future.The valuable results of this dissertation are following:1. Aqueous synthesis of CdTe and type-ⅡCdTe/CdSe core-shell quantum dotsIn this chapter, we report a two-step aqueous synthesis of highly luminescent CdTe and CdTe/CdSe core/shell quantum dots via a simple method. The emission range of CdTe/CdSe Quantum dots can be tuned from 510 to 640 nm by controlling the thickness of CdSe shell. Accordingly, the photoluminescence quantum yield (PL QY) of CdTe/CdSe quantum dots with an optimized thickness of the CdSe shell can reach up to 40%. The structure and compositions of the core/shell quantum dots were characterized by transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy, and the formation mechanism of the core-shell structure was discussed in detail.2. Labeling of aqueous type-ⅡCdTe/CdSe quantum dots in tumor cells as fluorescence probewe successfully labeled tumor cells—HeLa using aqueous, high emissive, and folate conjugated type-ⅡCdTe/CdSe quantum dots as fluorescence probe which were assessed with a fluorescence microscope. The results showed that folate conjugated CdTe/CdSe quantum dots could enter tumor cells efficiently, which showed good tracing and labeling of quantum dots in HeLa cells. The results indicated that the type-ⅡCdTe/CdSe quantum dots are a excellent fluorescence probe and could be applied in biolabeling.3. Synthesis of highly emissive Mn-doped ZnSe quantum dots without pyrophoric reagentsManganese-doped zinc selenide quantum dots (Mn:ZnSe d-dots) with high optical quality, pure dopant emission with 40-60% photoluminescence quantum yield, were synthesized with air-stable and generic starting materials, namely zinc (manganese) fatty acid salts with corresponding free fatty acids, Se powder, fatty amine, and octadecene. The pyrophoric, highly toxic, and expensive organophospines were eliminated from the existing synthetic protocols for high quality Mn:ZnSe d-dots, which changed the reaction profile substantially, because of the enhanced reactivity of elemental Se with the presence of fatty amines. The reaction temperatures for two key processes involved in "nucleation-doping", namely, formation of MnSe nanoclusters and their overcoating by the host, were both reduced. Multiple injection techniques were employed to realize balanced diffusion of Mn ions in the doped quantum dots (d-dots). The resulting d-dots were found to be in zinc-blende crystal structure, with optimal spherical shape, nearly monodispersed, and controlled in their Mn:Zn ratio.4. Investigation of synthesis and doping mechanism of Mn doped CdSe quantum dotsIn this chapter, we used the "nucleation doping" route to combine dopants and host materials and synthesized high-quality Mn doped CdSe nanocrystal emitters with nearly pure Mn emission and efficient dopant photoluminescence using selenium power as selenium source and carboxylic amine as active reagent. We investigated the effect of the ratio of carboxylic acid salts to carboxylic acid and the overcoating temperature of shell on the optical property of Mn doped CdSe nanocrtstals. The critical temperature of "lattice diffusion" of Mn ions in CdSe lattice was defined and a new "lattice ejection" mechanism was proposed, which is very valuable and interesting to the investigation of synthesis and mechanism of other doped quantum dots.