Study On Synthesis And Photoluminescence Properties Of ZnO, ZnO?S?ZnS?O And Their Core-shell Structure Nanoparticles

The visible luminescence mechanism of ZnO has been the focus of research,and it is very important to make a summary of the photoluminescence in the visible range.The photoluminescence spectrum can reflect some important information,such as surface deficiency and oxygen vacancies,the surface state of semiconductor materials,the photoinduced charge transfer process and so on.Some scholars think that the luminescence mechanism of ZnO is related to the crystal defects,and the researchers believe that the luminescence mechanism is related to oxygen vacancies.Therefore,this paper explains the visible light emission mechanism of ZnO in the field of quantum confinement effect,surface modification and defect control.The relationship between the change of the microstructure and the luminescent properties of the nanoparticles was discussed,and the fluorescence properties were controlled by the growth mechanism and microstructure of the quantum dots.Therefore,the main research contents and results are as follows:?1?ZnO nanoparticles were prepared using direct precipitation method and hydrothermal method,respectively.The XRD analysis showed that the sample had a hexagonal wurtzite crystal structure and the average particle size was 3.9 nm and 34.1nm,respectively.The diffraction peak of hydrothermal method is stronger than that of precipitation method,which indicates that the crystallinity is higher.The results of scanning electron microscopy?SEM?and transmission electron microscopy?TEM?showed that the ZnO nanoparticles were spherical and flaky.The emission spectra show that the PL intensity of Hydrothermal synthesis of particles are better than that of the precipitation method.?2?ZnO/ZnO core-shell nanoparticles were prepared by direct precipitation method and hydrothermal method,respectively.The effects of the thickness of ZnO shell on the particle size,structure and luminescence of ZnO/ZnO core-shell structure were studied.The SEM and TEM showed that the samples were spherical and flaky,respectively.The results of PL showed that the photoluminescence properties of ZnO prepared by the two methods were increased by ZnO coating.The maximum photoluminescence intensity of ZnO/ZnO core-shell structure synthesized by direct precipitation method and hydrothermal method was about 2 times and 4 times as high as that of the ZnO sample,respectively.According to the UV visible transmission spectrum,the average band gap widths of the ZnO/ZnO core-shell structures obtained by direct precipitation methods is 3.32 eV,which shows that the width of the band gap will be reduced after the ZnO nanoparticles are coated.Because when the ZnO nanoparticles are coated,surface defect state were reduced by the coating,the free carrier concentration increased at the same time,this resulted in a downward shift of the Fermi energy to the conduction band and get close to the top of the valence band,the electron transition occurs between the conduction band and the Fermi energy,so the band gap decreases.?3?Under the condition of 15 h and 90?,The core-shell structure of graphene/ZnO was synthesized using a hydrothermal method.Experimental results show:the sample had a hexagonal wurtzite crystal structure.The luminescence intensity of the samples increases with the increase of the graphene concentration,and then decreases.The maximum luminous intensity of the sample is about 3 times as high as that of the ZnO nanoparticles.The result showed that the formation of core-shell structure with graphene can enhance the photoluminescence intensity of ZnO nanoparticles.Graphene lead to a decrease in the surface defects of ZnO and then resulted in an increase in photoluminescence intensity.?4?Synthesis of ZnO:S^2-nanoparticles by direct precipitation method.The results show that the sample had a hexagonal wurtzite crystal structure.The SEM showed spherical shape and the particle size was about 40nm.The PL intensity of ZnO:S^2-nanoparticles first increased and then decreased with the increase of S^2-doping concentration,which was higher than that of ZnO.S^2-can replace the O^2-into the lattice of ZnO,and resulted in the lattice distortion to form new defects to enhance the fluorescence intensity of ZnO in the visible region.?5?ZnS:O^2-nanoparticles were prepared by solid state reaction method.XRD showed that the crystallinity of the samples decreased gradually,which indicated that the S^2-was replaced by O^2-into the ZnS lattice.The morphology of ZnS:O^2-samples was spherical and the particle size was in the range of 40-130 nm.The emission peak position of the sample appears blue shift with the increase of O^2-concentration.When the Zn/O was 10:5.3,the emission intensity reached the highest.This proved that the doping of O^2-can improve the PL intensity of ZnS.?6?ZnS:O^2-/ZnO nanoparticles were obtained by direct precipitation method.The results showed that:With the increase of ZnO coating,the diffraction peaks of ZnS and ZnO appeared simultaneously.With the increase of ZnO content,the PL intensity of ZnS:O^2-nanoparticles increases first and then decreases.One explanation could be that the coating of ZnO play the role of surface modification,which can lead to the decrease of surface defects of ZnS:O^2-and then resulted in an increase in photoluminescence intensity.The increase of ZnO increased the size of the whole particle,leading to the decrease in PL intensity.