Study On The Preparation And Growth Mechanism Of Aqueous CdTe Nanocrystals

Highly fluorescence (PL) semiconductor nanocrystals (NCs) have wide applications in optoelectronic conversion, sensor, optical display, and especially biological imaging. Aqueous methods have been developed to prepare II-VI NCs, especially CdTe NCs. Since the first synthesis of 1-thioglycerol stabilized CdTe NCs in aqueous media was reported, various thiol ligands have been used for aqueous CdTe NCs. However, less works focused on the growth mechanism of aqueous NCs due to the complexity of aqueous system. It becomes urgent affairs for the further study on the growth principle of the aqueous NCs.In this thesis, our aim is to build up the structure model of aqueous NCs and investigate their growth principle. The effect of different experimental conditions on the nucleation, growth process and fluorescence properties was systemically studied.(1) We developed a new method for the aqueous citrate sodium-assisted preparation of aqueous CdTe NCs. This atrategy breaks through the limitation of the convetional mercapto group aqueous phase method with ligands and precursors, which is helpful to further study the effect of the ligand and its shell on the growth of NCs. The theoretical calculation and analysis for the effect of ligand shell on the growth process of NCs were carried out. It was found that in the presence of the very low concentration of mercapto groups ligands, the mercapto groups is prone to enrichment on the NCs surface.(2) Through the study of the effect of the adsorption layer on the properties of CdTe NCs during storage at room temperature, we found that the excess ligands or cadmium-ligands compounds in solution are preferentially adsorbed on adsorption layer before they diffuse into the ligand shell. The adsorption layer can affect the diffusion process of free ligands or cadmium-ligands compounds into the ligand shell.The treatments of dilution, concentration, storage, and pH adjustment for the NCs solution could affect the thickness of adsorption layer as well as the ligand diffusion into ligand shell, leading to diverse optical behavior of NCs.