Surface Modification, Self-Assembly And Optical Properties Of ZnO Nano-Crystals

As a wide band gap semiconductor material possesses large exciton binding energy of 60 meV at room temperature, ZnO is rationally expected to be promising candidates for room-temperature UV laser or other interesting phenomena involving excited states. ZnO nanocrystal is an exceptionally important material for the envisaged applications in many technologies, such as solar energy conversion, and optoelectronic devices. Sol-gel process is well known as a versatile technique that can control the purity and homogeneity at molecular scales without any requirment of special equipments. Also is sol-gel technique widely employed in fileds of synthesis of various materials for its other advantageous qualities such as low cost and enviementally friendly nature. This thesis is focused on the hotspots and challenges in the field of ZnO materials research. ZnO nanocrystals were synthesized via sol-gel technique and its optical properties were investigated. The following is the major results: 1. ZnO nanocrystals with high UV luminescence is prepared via sol-gel technique, and its optical properties were studied. Based on the temperature dependent relationship of integral intensity of free-exciton, peak energy and linewidth that revealed by temperature dependent photoluminescence of ZnO nanocrystals, the influence of aging upon optical properties of ZnO nanocrystals was discussed. Surface modification of ZnO nanocrystals is carried out by sol-gel technique. ZnS enveloped ZnO notably enhanced the chemical stability of ZnO cores, and qualified the ZnO nanaocrystals for further bio-conjugation. 2. Monodispersed ZnO colloids with different diameters were synthesized by sol-gel process. The effect of experimental condition on the morphology and properities of the resulting ZnO were investigated. Monodispersed colloids were self-assemblied into 3D colloidal crystals of opal structure which exhibites weak pseudogap. 3. ZnSeO nanocrystalline film is prepared by annealing of ZnSe film at low temperature. Its structure and optical properities were investigated. Transmutation from ZnSe to ZnSeO and then to ZnO took place at the annealing temperature ranging from 450℃to 550℃. Topologic and phase imaging by atomic force microscopy indicates that specific structure appeared at this temperature interzone. Optical properities of specimen annealed at low temperature revealed that the resultant ZnO have obvious quantum confinement effects on ZnSe.