Synthesis And Properties Of ZnS Based Nanocrystal

In this paper,a series of ZnS,ZnS:Eu³⁺,ZnaexS1-x nanocrystal were synthesized by oil phase thermal solution injection method and hydrothermal method,which was simple,low cost,and environmentally friendly.The band structure and density of states of ZnS,Zn:Eu³⁺,ZnSexSi1-x were obtained using first-principles.The properties of the as-synthesized nanocrystal were characterized by XRD,SEM,TEM,photoluminescence and UV-vis absorp-tion spectra.The main contents as following:（1）On the base of a 1×1×2 cubic ZnS super cell,a series of model with different defects was built by adding or deleting an atomic.The formation energy of different defects and the electronic structure of ZnS was calculated by using first principle and the influence of different defects on the energy level and density of state has been analyzed.ZnS nanocrystal with different ratio of Zn/S was prepared by oil phase thermal solution injection method and XRD patterns shown that all obtained products belong to the cubic sphalerite structure.The TEM indicated the particles are approximately spherical and have a good dispersion.The obvious lattice fringe could be seen from HRTEM patterns and the diameter is in the range of 3 nm to 7 nm.The emission and excitation spectra of the samples were measured and what could be known is that the different ratio of Zn/S have huge effect on the properties of ZnS nanocrystal.（2）The Eu³⁺ doped ZnS atomic model was built by replacing one or two Zn atomic using Eu atomic in a 2×2×2 cubic ZnS super cell,and their electronic structure was calculated by using first principle and the influence of different doping concentration on the energy level and density of state has been analyzed.A series of ZnS:Eu³⁺ nanocrystal was prepared by oil phase thermal solution injection method and XRD patterns shown that the cubic sphalerite structure of ZnS still exist after Eu³⁺ ion doping.The TEM indicated the particles are approximately spherical and the diameters are increasing gradually with the increase of the doping concentration.From HRTEM patterns,obvious lattice fringe could be seen.There are characteristic peaks of Eu in the EDS analysis pattern.The photoluminescence spectra were also measured and characteristic emission and excitation peaks of Eu³⁺ appeared.The emission peaks located at 595,621 and 701nm and the intensity of the peak at 621nm is the strongest.The excitation peak located at 395nm has the biggest intensity.With the increasing of the doping concentration,the color coordinates gradually close to the white light area.（3）A series of ZnSe_xS_1-x（x=0.20,0.33,0.50,0.67,0.80,1.00）space model were built on the base of cubic ZnS super cell and their electronic structure was calculated by using first principle and the influence of different x value on the energy level and density of state has been analyzed.ZnSe_xS_1-x nanocrystal was prepared by oil phase thermal solution injection method and it could be find that with x value becoming bigger,the XRD diffraction peak shift to small angle,the diameter of nanoparticles gradually increased from 3.74 nm to 4.33 nm.The emission peak appeared red shift from 518 nm to 544 nm and excitation peak from 423 nm red shift to 475 nm.（4）ZnS crystallite with different conditions was synthesized through hydrothermal method.The crystallite belongs to the cubic sphalerite structure.There are two emission peak resulted from the sulfur vacancy and zinc vacancy defect in the emission spectra,and the relative intensities of the two emission spectra change with the ratio of Zn/S.The crystallite repared by different ratio of water and absolute ethanol is spherical and the optimal ratio is 1:1.