Studies Of The Preparations And Optical Properties Of ZnS/Organic Nanocomposites

In the past decade, ZnS nanoparticles have been investigated intensively due to their excellent optoelectronic properties. ZnS is a typical direct broad bandgap â…¡ ^â…¥ group compound semiconductor. Its bandgap is 3.66 eV at room temperature. With the decrease of ZnS nanoparticle size, it shows significant quantum-size effect. Controlling over both nanocrystal morphology and crystal size is always an important factor to tune the optoelectronic properties of ZnS nanocrystals. ZnS nanoparticles of excellent optoelectronic properties have been obtained by modifying the surfaces of them with organic substance and varying the reaction condition. ZnS nanostructures have great potential applications in electroluminescence, field emission flat plate display, optoelectronic diode, light electrode, cell battery, dielectric filtering, infrared window, sensing device, laser etc. In this thesis, the preparations of ZnS nanostructures and optical properties concerned about them have been discussed.The main works and results of the thesis are as following:ZnS nanoparticles were modified by dodecylthiol and stabilized by poly(vinyl alcohol) (PVA). UV-VIS spectra and PL spectra results indicate that ZnS nanoparticles exhibit significant quantum size effect by varying the reaction condition.A novel ultraviolet-irradiation technique had been successfully developed to synthesize ZnS nanocrystals , using poly(vinyl alcohol)(PVA) as protecting agent. The produced ZnS nanocrystals can exhibit spherical and wire-shaped morphologies by adjusting the complex reaction time and irradiation time. According to the results of experiments, the possible mechanism was proposed. The optical properties of ZnS nanocrystals can be influenced by varying the reaction condition.ZnS nanostructures including nanoparticles and one-dimensional nanocrystals were obtained by in-situ synthesis in Aa-AMPS-hT ternary copolymer network. Aa-AMPS-hT as SAM is a polymer providing strong chelation ability with Zn²⁺ due to its sulfonic group. UV-VIS spectra and PL spectra results indicate that ZnS nanocrystals exhibit significant quantum size effect by varying the reaction condition.Pure phase hexagonal wurtzite ZnS nanowhiskers were obtained by solvothermal method, using ethylenediamine as solvent. ZnS nanowhiskers have diameters ranging from 6nm to lOnm and length of 1.2 u m. The ratio aspect of ZnS nanowhiskers is nearly 200. XRD results show that the diffraction peak of (002) was intenser than the standard value. This intenser and narrower diffraction peak of (002) indicates a possible preferential orientation along the c axis. UV-VIS spectra and PL spectra results indicate that ZnS nanocrystals exhibit significant quantum size effect with increasing the reaction time at 120°C.Long ratio aspect ZnS nanotubes and nanowires were synthesized by a simple PVA-assisted ethylenediamine solvothermal method. The nanotubes are 2.5 umin length. The outer diameters of nanotubes range from 20nm to 50nm while the wall thicknesses are in the range of 5-20 nm. The inner diameter of nanotubes is around lOnm. The ZnS nanowires are uniform in diameter of around 50nm and of 7 u m in length. In addition to straight nanowires, winding ZnS nanowires were also obtained. The bending ZnS nanowires are not reported in previous works. These nanostructures show significant quantum size effects. It is expected that this method could be used to prepare other metal sulfide nanotubes.