| Due to quantum size effects, semiconductor quantum dots (QDs) exhibit size-dependent and shape-dependent physical properties, which greatly differ from those of the corresponding bulk materials. Due to such excellent properties, these QDs have potential applications in different technological areas including biomedical tags, light-emitting diodes, laser, and solar cells. As a direct bandgap semiconductor, CdS nanocrystals may be potentially used in solar cells. There are many factors that will effectively influence the properties of semiconductor QDs, including size, shape, size distribution and phase structure. So we can modify the chemical and physical properties of semiconductor QDs through tuning those factors. So far, the most popular route to CdS QDs is organometallic precursor method,however, this method has many disadvantages. In this dissertation,the present study addressed our efforts on the development of two different synthesises to colloidal photoluminescence (PL) CdS QDs in green chemical reaction system, the effects of reaction time, growth temperature, precursor molar ratios on the size, size distribution, shape, and structure of QDs have been investigated. The main achievements are listed as following:(1) A new solvent system was developed to prepare colloidal photoluminescence (PL) CdS QDs via hot-injection synthesis. CdO and elemental sulfur powder were used as Cd and S sources, respectively. In our work, N-oleoyl-morpholine was used as the solvent of S instead of ODE, while ODE only acted as reaction media. Sulfur powder could be dissolved in N-oleoyl-morpholine at room temperature. OA was used as capping agent.(2) The particle size and the luminescence of CdS QDs were largely affected by the reaction temperature, the concentration of OA and the initial Cd/S ratio. Usually, the size increased with an increase of reaction temperature. When the concentration of OA increased, larger final particle sizes were formed and intensity defect band became stronger. As the Cd/S ratio increased, the growth rate became low, the size distribution became narrower and little trap emission could be observed. The feed molar ratio of 3Cd/1S was proved to be the optimal synthetic window, together with the OA concentration of 1.5 mL and growth temperature of 210℃. The route enables us to obtain high-quality CdS QDs with size ranging from 2.26 to 4.41 nm. The narrowest PL FWHM was 16 nm. Typical HRTEM images revealed that the as-prepared CdS quantum dots had narrow size distribution and high crystallinity.(3) The usual hot injection synthetic method is not suitable for large-scale, industrial preparation. To overcome this difficulty, we report a one-pot colloidal synthesis of high-quality QDs. A green simple system was developed to prepare high quality monodisperse CdS QDs, using ODE as the solvent of S powder, cadmium oxide as Cd sources, and oleic acid as capping ligands. The XRD and HRTEM measurement showed that the as-prepared CdS QDs were zinc-blende structure, highly monodisperse and well crystalline.(4) The key roles of both the growth temperature and the initial Cd/S ratio in determining the size, photoluminescence quantum yields (PLQY) of CdS QDs have been extensively investigated employing a one-pot synthesis. They exhibit the emission of fluorescence is dominated by band-gap luminescence. The PL spectra are symmetrical, and their full-width at half-maximum (FWHM) is samll. The first absorption peak is very sharp. The synthesized CdS QDs not only have a high monodisperse size distribution, but also exhibit high-quality optical properties. It has been demonstrated that by a judicious choice of the Cd:S ratio(3:1) and the growth temperature (240℃) highly photoluminescence quantum yields nearly monodisperse CdS nanocrystals may be obtained, without any postpreparative treatment,it enabled us to achieve high quantum yields (about 30%).
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