Preparation And Luminescence Properties Of ZnS:Mn/ZnS Composite Materials

Semiconductor luminescence materials possess many excellent and unique properties, As a II-VI direct wide band gap semiconductor, ZnS material has the most excellent performance, ZnS doped can also obtain better luminescence properties. However, because there are a large number of defects on the surface of materials, these defects can act as a fluorescence quenching center and then cause non radiative recombination, which leads to the decrease of the luminous efficiency. Using the surface coating modification treatment of the materials can effectively decrease defects of surface state and improve the luminous efficiency. The study on the preparation and optical properties of ZnS and doped luminescence material, and the surface modification of their, will be beneficial to enhance the luminescent properties of the material, which has the important theory and the practical application value.In this study, The ZnS:Mn luminescent materials were firstly prepared by hydrothermal method using zinc acetate as the zinc source and thiourea as the sulfur source. The structure, morphology and luminescence properties of ZnS:Mn luminescent materials were characterized by means of XRD, SEM, TEM, HRTEM, PL spectr and UV-Vis. Then ZnS:Mn/ZnS composite materials were fabricated by Larmer method using zinc nitrate as source of zinc, sodium sulfide as sulfur source.The luminescence efficiency of ZnS:Mn/Zn S composites prepared with different coating concentration and different coating layers was studied, and a preliminary study on the luminescence mechanism of ZnS:Mn/ZnS composite luminescent materials was carried out. The specific research contents are as follows:The ZnS:Mn luminescent materials were prepared under different Mn doping content, Zn:S ratio, reaction temperature and reaction time. The study found that the ZnS:Mn luminescent materials prepared by the solvent thermal method had a high crystallinity and with the structure of wurtzite. No other diffraction peaks are observed in the diffraction pattern, which indicated the product of ZnS:Mn is pure phase. The structure of ZnS: Mn have not changed with the increasing amount of Mn dope, but the diffraction peak of ZnS: Mn shifts to the left, indicating that Mn2+ enters the ZnS lattice.It was found that the structure of ZnS:Mn prepared under different conditions is wurtzite, but the preparation condition had a great influence on the morphology of the luminescent materials. Using four factors and four levels orthogonal experiment to optimize the preparation condition of ZnS:Mn( Zn:S=1:2, Mn content 1%, 220 oC, 14h). Combined orthogonal experimental method and luminescence performance, the research results of the ZnS coating show that coating the structure of ZnS:Mn has been not effected by the ZnS coating, but the diffraction peaks of ZnS:Mn/ZnS are shifted to the left and the migration degree increases with the increase of coating ratio. With the increase of the ratio of ZnS coating, the particles on the surface of ZnS:Mn showed a gradually increasing trend. the approximate hexahedron morphology of ZnS:Mn were not significantly influence by the different layers of the ZnS coating. with the increase of coating layers, the particles to the surface of the ZnS: Mn gradually show the trend of becoming large and more.The luminescence properties of ZnS:Mn prepared at different Mn doping content, Zn:S ratio, and different reaction time and reaction temperature were studied. The result indicated that the luminescence intensity in 390nm~450nm is affected by the S vacancy in ZnS and the surface defect states of ZnS. The luminescence intensity in 580nm~600nm come from the electronic transitions of 4T1-6A1 in Mn, at the same time, was influenced by S vacancy in ZnS:Mn and the surface defect state of ZnS:Mn.The study of composite materials(Zn:S=1:2, Mn=1%, 220 oC, 14h) with different coating ratio of ZnS:Mn and ZnS and the coating layers of ZnS showed that the matching of the crystal lattice of ZnS:Mn and coated ZnS is better, the surface of ZnS:Mn is not smooth, and the lattice fringes at the grain boundaries are staggered, which may lead to the effect of certain degree of tension of ZnS on ZnS:Mn. However, with the increase of the coating ratio and the coating layers, the thickness of the coating layer increases, and the orientation of ZnS particles in the coating layer away from the interface is randomly distributed.The study of ZnS:Mn/ZnS composite materials(Zn:S=1:2, Mn=1%, 220 oC, 14 h and Zn:S=1:2, Mn=6%, 210 oC, 12h) with different coating ratio of ZnS:Mn and ZnS(0,0.05,0.10,0.15,0.20,0.25) showed that the coating ratio has a significant effect on the luminescent properties of the materials, and the luminescence intensity increases gradually with the increase of the coating ratio. When the coating ratio is 0.1, the luminescence intensity of ZnS:Mn/ZnS composite materials(Zn:S=1:2, Mn=1%, 220 oC, 14h) reaches the maximum, and then the luminescence intensity decreases with the increase of the coating amount. When the coating ratio is 0.05, the luminescence intensity of ZnS:Mn/ZnS composite materials(Zn:S=1:2, Mn=6%, 210 oC, 12h) reaches the maximum, and then the luminescence intensity decreases gradually with the increase of the coating amount, and slightly elevated later. ZnS:Mn/ZnS composites materials with different layers of coating ZnS(the ratio of ZnS to ZnS:Mn in each layer are 0.05) were prepared. When coated the first layer, the luminescence intensity of ZnS:Mn/ZnS composite materials(Zn:S=1:2, Mn=1%, 220 oC, 14h) reaches the maximum and is obviously increased than that without coating, and then the luminescence intensity decreases with the increase of the coating layers. When coated the first layer, the luminescence intensity of ZnS:Mn/ZnS composite materials(Zn:S=1:2, Mn=6%, 210 oC, 12h) reaches the maximum and is obviously increased than that without coating, and then the luminescence intensity present the trend of decreasing first and then increasing with the increase of the coating layers.The luminescence intensity increases due to the decrease of the surface quenching center. At the beginning, with the increase of the coating ratio and the coating layer, the surface quenching center decreases, and the luminescence intensity increases gradually. However, with the increase of the ratio of the coating and the coating layer, the thickness of the coating layer becomes larger, the non radiative transition increases, and the luminescence intensity is reduced.The luminescence properties of ZnS:Mn/ZnS composites prepared by different coating ratio and coating layers are affected by many factors,which included the energy level of discrete luminescent center Mn2+, the intrinsic energy level and defect energy levels of matrix ZnS, the interface state of ZnS:Mn and ZnS, the interface bonding state of ZnS:Mn and ZnS, as well as the state of the ZnS coating layers. UV-Vis results show that the corresponding interface bonding were obtained due to the different ZnS:Mn under different ZnS:Mn in different coating ratio and coating layer, which leads to the grain size of produced ZnS coating on the surface of ZnS:Mn will also be different. The position of the different absorption band edge will be changed under the action of the various factors.