Preparation And Luminescent Properties Of Core-shell Structured Rare Earth Oxysulfide Nanocrystals

During the past few years,intensive research efforts have been focused on the development of rare earth doped upconversion luminescent(UCL)materials.Among them,lanthanide-doped oxysulfide,presents promising applications in broad areas as an excellent luminescence material.In this thesis,core-shell structured rare earch oxysulfide nanocrystals were prepared by the homogeneous co-precipitation method,and luminescence properties of these nanocrystals were studied.The main research contents and results are shown as below:1.Core-shell Y2O2S:Er3+ @ Y2O2S:Yb3+,Tm3+ upconversion(UC)nanoparticles were synthesized by the homogeneous co-precipitation method combining with the solid-gas sulfidation route.Photoluminescence spectra were used to characterize the optical properties.1G4?3H6 transition of Tm3+,4S3/2,2H11/2?4I15/2 and 4F9/2?4I15/2 of Er3+ can be observed in Y2O2S:Er3+ @ Y2O2S:Yb3+,Tm3+ under 980 nm excitation.Simultaneously,emissions of Er3+ and Tm3+ ions confirm the occurrence of energy transfers of Yb3+?Tm3+ process in the shell layer and Yb3+?Er3+ process from shell layer to core layer.Observation of 3H4?3H6 transition of Tm3+ ions at 1550 nm excitation further verifies the energy transfer of Er3+?Yb3+?Tm3+ between core and shell layers.2.The homogeneous co-precipitation method combining with the solid-gas sulfidation route was adopt to prepare the core-shell Y2O2S:Er3+ @ Y2O2S:Yb3+,Ho3+UC nanoparticles.Core-shell Y2O2S:xEr3+ @ Y2O2S:8%Yb3+,1%Ho3+ samples presented green emission under 980 nm excitation,and optimal doping concentration of Er3+ is 12%,whereas the Y2O2S:12%Er3+,8%Yb3+,1%Ho3+ sample shows red emission.Spectra analyses revealed that UCL of Y2O2S:Er3+ @ Y2O2S:Yb3+,Ho3+ was managed by the Ho3+ ions(5S2,5F4?5I8 transition).Er3+ ions play a dominant role in the UCL of Y2O2S:Er3+,Yb3+,Ho3+ sample.Furthermore,Er3+(core)?Yb3+(layer)?Ho3+(layer)energy transfer processes can be further confirmed by the emission of Ho3+ under 1550 nm excitation.3.The homogeneous co-precipitation method combining with the solid-gas sulfidation route were employed to prepare Y2O2S:Er3+ @ Y2O2S @ Y2O2S:Yb3+ UC nano-particles.Emission intensities of Y2O2S:Er3+,Y2O2S:Er3+ @ Y2O2S and Y2O2S:Er3+@ Y2O2S @ Y2O2S:Yb3+ present an increasing trend both under 980 and 1550 nm excitations,green and red emission components gradually increase under 980 and 1550 nm excitation,respectively.This improvement of UCL efficiency confirms the formation of core-shell structure.