Study On The Synthesis And Optical Properties Of Zinc Oxide Nanocrystallines

Nanomaterials means materials in nanometer (1-100 nm) with at least one dimension in space or materials made up of units in nanometer. Because of its unique properties including surface effect, volume effect and quantum confinement effect different from bulk materials and single molecular and the promising application values in areas such as electronics, optics, chemistry, ceramics, biology and medicine, it invokes much interest among researchers all of the world. Fabrication of materials is the basis of property study. Synthesis and preparation of nanomaterials goes deeper with the understanding of their unique properties. Synthesis and preparation of zero-dimensional materials has been made great development since the eighties of twenty century. But the synthesis of one-dimensional (1D) and two-dimensional (2D) materials is challenging. Because of its special electronic, optical, magnetic and mechanical property, it will be the key problem for the application in microelectronics and nano-electronics and will be the emphases of nanomaterials research for a long time.ZnO is a direct and wide band gap semiconductor of II -VI group with an energy gap of 3.37eV at room temperature. Nanostructured ZnO materials are the excellent unity of nanomaterials and semiconductors and have the promising applications in LCD displays, solar cells, protecting coatings, gas sensors, solid illuminations and UV optical devices. The method for preparation of ZnO nanomaterials can be divided into physical methods and chemical methods among which, the chemical solution method is favorable because it is simple, cheaper and need no expensive apparatus. But the chemical process is complicated and the reaction mechanism is not well understood.This paper is interested in synthesizing and preparing nanostructured ZnO crystalline. 1D and 2D ZnO nanomaterials have been synthesized with the combination method including precipitation method, hydrothermal method and polymer template method by controlling the parameters such as reaction time, pH value, temperatures, and concentrations. Phase compositions and microstructures were studied by XRD, TEM/HRTEM, SEM techniques. XPS, FTIR, UV-Vis absorption, PLspectra were used to study the spectra characterization. The photoluminescence property of rare earth doped ZnO nanocrystals were studied also.Hexagonal wurtzite ZnO nanorods have been prepared by precipitation and hydrothermal method with surfactant CTAB as additives. The results show that increase of pH value of the initial solution, the aspect ratio of the nanorod decreased and the nanorods changed from rod-like to spindle-like morphology. Oriented attachment mechanism was used to explain the growth mechanism of the nanorods. CTAB absorbed on the surface of the nanocrytals and act as a transporter, which made the nanocrystals aggregate and easy to attach. Non-perfect oriented attachment leads to defects on the surface of the nanorods resulting in UV-Vis absorption red shifted. By annealing the nanorod crystals in ammonia gas, the PL spectra show obvious UV near band-edge emission. While annealing the crystals in air, the orange emission was greatly enhanced.Complicated ZnO morphologies were obtained by using the mixture of polymer and surfactant as additives when prepare ZnO nanocrystals under hydrothermal method. The polymer and surfactant can affect each other in the solution and form a kind of compound. The temperature, concentrations and other factors can affect the compound and in turn affect the morphology of the nanocrystals. The morphology of nanomaterials can be controlled by this method.Two-dimensional ZnO nanosheets have been synthesized by hydrothermal method with urea as the homogeneous precipitant. The thickness of the nanosheet is about 40 nm and the length of the boarder reaches micrometer. The nanosheets has network structure with macro pores. Urea has played the key role in forming the sheet-like ZnO nanomaterials. NiO nanowire was also prepared with urea as homogeneous precipitant by solution method under normal pressure. Arrays of NiO nanorods and aggregations of NiO nanocrystals were obtained when the reactant were treated under hydrothermal condition. These results indicate that urea is an excellent precipitant and controller in synthesizing nanomaterials.Rare earth doped ZnO nanocrystals were studied. XRD results show that the diffraction peak widened and intensity decreased with the increase of rare earthconcentrations in the ZnO nanocrystals which means that the size of the ZnO nanocrystals decreased. The doping of rare earth ions can hold back the growth of ZnO nanocrystals. The characteristic photoluminescence of Ce3+ was observed in Ce doped ZnO nanocrystals. Strong blue photoluminescence was observed in 1 at% Ce doped ZnO nanocrystals. The doping La ions can affect the visible photoluminescence of ZnO nanocrystals.This paper developed and improved the system of ZnO nanomaterials. The preparation method can be applied to prepare other metal oxides. The experimental results are the basis for the application and development of ZnO nanomaterials.