Preparation And Luminescent Properties Of Nanocrystalline ZnO And ZnO:RE

Lü Shuchen(Condensd Matter Physics)Directed by Prof. Huang Shihua Preparation and room temperature emission of nanocrystalline ZnO, colloidal ZnO solutions and rare earth doped nanocrystalline ZnO are presented in the present paper, including the near infrared and upconversion luminescence. The main contents and the important results are as following: Nanocrystals ZnO are prepared by chemical precipitation. Crystal structure and ceramoc microstructure of powder samples are examined by XRD and TEM. The mean grain size of the materials ranges from 10nm to 50nm by controlling the reaction concentration and annealing temperature. The results indicate that there exists a critical concentration which makes the size of nano-ZnO smallest under the same annealing temperature and that the dependence of the mean grain size on the reaction concentration is nonlinear. The luminescence properties of the unannealed samples show that the band gap luminescence is predominant and the green defect induced luminescence, typical of ZnO, is strongly quenched. Two weak features located at 450nm and 492nm are observed. The samples annealed at high temperature exhibit intense green emission, but the spatial distributions of the band edge luminescence and the green emission are not completely complementary as the annealing temperature is increased. The common feature of the emission spectrum observed in the nanocrystalline ZnO is that its width is larger than that of the bulk ZnO. The mechanism behind the visible green luminescence is attributed to the transition between O vacancies and Zn vacancies. Colloidal chemistry techniques are used to synthesize ZnO particles in colloidal suspensions. The mean grain size of the ZnO particles is less than 5nm. A simple, but practical theoretical mode established in this paper is used to describe the dependence of the particles size on the reaction, where the experiment data of optical absorption have been employed in the model. In addition the surface-modified ZnO nanoparticles are found to enhance the band edge luminescence. We have made a great breakthrough in the preparation of ZnO:RE. The nanocrystalline ZnO:RE powders with room temperature sharp photoluminescence have been prepared successfully for the first time in this paper. This is a great progress in the studying history of rare earth doped ZnO. For the ZnO:Er obtained in the present paper, the room temperature sharp characteristic emissions from the trivalent rare earth Er3+, including upconversion and near infrared emissiom, and the energy transfer between the nanocrystalline ZnO host and the dopants are observed for the first time in this paper. For the ZnO:Eu obtained in the present paper, Eu3+ ions have successfully inserted into ZnO host lattices with two different structure phases. The selective excitations are used to differ from the two different symmetry sites. The charge transfer state of Eu3+ ions is observed for the first time in the ZnO host.