Study On Synthesis, Characterization, Optical Properties Of Ⅱ-Ⅵ Semiconductor Nanocrystal By Hydrothermal Process

In most of semiconductor materials, II -VI nano semiconductor materials have been investigated and extensively used, for their quantum size effect, special shape, nonlinear optical and luminescence. In this dissertation, CdSe nanoparticles and CdS nano-rods have been successfully synthesized by hydrothermal method, and their properties and growth mechanism have also been studied and investigated. The main content of this thesis is as follows:1. With the oleic acid surfactant replacing the original expensive and toxic reagents of TOPO and TOP, CdSe nano-sphere has been successfully synthesized by hydrothermal method under a water-oil system. The shape, composition and properties of the product can be adjusted by changing the ratio of the reagent, reaction time and temperature. The product is characterized by various methods, such as powder X-ray diffraction (XRD), ultraviolet-visible absorption spectrum (UV-vis), photoluminescence (PL) and transmission electron microscopy (TEM). The XRD analysis revealed that the crystal structure of CdSe product is cubic phase. The TEM photo showed that the CdSe nanocrystals are of good dispersibility with diameter about 15-18nm. The ratio of the reagent, reaction time and temperature dependence of UV-vis spectra and the PL spectra of the CdSe nanocrystals have been revealed by the result of the experiment which also analysized the mechanism of the two peaks at 317nm and 358nm. Meanwhile, the best condition of the reaction has been revealed. 2. CdS nanorods were directly synthesized in a solvent of ethylenediamine (en) and an equal volume mixed solvent of en with water by a hydrothermal route respectively. The optical properties (UV-vis, PL) and shape (TEM) of CdS nanorods are uesd to show the differences between the two solvents. Moreover, the product is also characterized by XRD, which reveals that the crystal structure of CdS product is hexagonal phase structure. The best condition of the reaction has been revealed by comparing the shape of nanorods prepared with two different solvents. The PL spectrum of CdS nanorods consist of two emission peaks centered at 330nm and 346nm, which associate band edge emission and trap emission respectively. The thesis also discusses the influence of surface trap on the PL spectrum and the shape of nanorods with the analysis into the mechanism of en used as the surfactant in preparing CdS nanorods.