Photoluminescence Characteristics Of Zinc Sulfide Doped By Thermal Diffusion Of Halogen In Gas Phase

Zinc sulfide (ZnS) has been used as a host material of the conventional luminescence. ZnS has wide energy band gap (Eg) of 3.74 eV at room temperature, which make it easy to induce defect energy levels in its forbidden band. In other hand, its advantage of high temperature resistance and the wide energy gap provide the potentiality to realize different light emitting by doping appropriate activator impurity. And this material's practical significance in producing multi-color display has attracted many scientific researchers' attention for many years. In the present study, the photoluminescence characteristics of zinc sulfide doped by thermal diffusion of halogen in gas phase were systematically investigated.The main results of this study are as following: ZnS phosphor powder was prepared by halogen thermal diffusion in gas phase. In the experiment, we prepared ZnS material by chemical synthesis at first in order to exclude the disturbing impurities such as copper (Cu), manganese (Mn), etc by analysis of atom absorption spectrum. The thermal diffusion was selected as the main method of doping, and the halogen was used as the dopant. Concretely, we prepared blue light emitting ZnS powders by doping chlorine (Cl) and bromine (Br), respectively. The experimental conditions were preferred for preparing blue light emitting ZnS phosphor. Firstly, as for the diffusion temperature, we have tested the preferential range of 700 -1000 "C in which the blue light emitting ZnS powder could be prepared. When excited by ultraviolet radiation of 365 nm at room temperature, the sample emitted a blue photoluminescence. Secondly, the other influence factors, such as the diffusion duration of halogen and the protective ambience, on the photoluminescence of ZnS phosphor was studied. The test halogen diffusion duration and protective ambience were preferred for one hour and argon, respectively. Thirdly, an aging test of the blue light emitting ZnS powder was conducted at different temperature and in differentambience. The aging effect of blue light emitting ZnS powder was tested at 400 -1000 in argon (Ar), oxygen (02) and in air, respectively. The results show that the blue light emitting ZnS powder can work after one hour annealing below 900 癈 in inert ambience such as Ar, and below 500 癈 in oxygen or in air.A tentative light emitting mechanism for the sample of Cl-doped has been proposed, which is supported by experiment phenomena, X-ray diffusion (XRD) and transmitting electronic microscope (TEM) analysis. By analyzing the phenomena of doping and aging experiments, the mechanism of the light emitting ZnS samples can be summarized as following: The blue light emitting comes from the recombination of D-A couple in which the donor energy level is located 0.615 eV below the edge of conduction band and VznCls impurity (acceptor) level is located at 0.44 eV above the edge of valence band. The green light emitting is the result of the recombination between the electrons in the conduction band and ionized vacancy, Vzn" , which is deep energy level defect located 1.22 eV above the valence band.Finally, an attempt has been made to prepare a luminescence film of Cl-doped ZnS by means of electrophoresis method. The electrophoresis deposition thin film shows the same photoluminescence characteristics as the as-prepared phosphor of Cl-doped ZnS and the relationship between the photoluminescence intensity of the films and the density of ZnS suspension was investigated.