Research On Thermal Diffusion Of Eu³⁺ In YVO₄:Eu³⁺@YVO₄Core-shell Luminescent Nanomaterials

ABSTRACT:Core-shell structure has been used to weaken surface effect and raise luminescent efficiency of nano-materials. The shell can provide a protective layer, isolate the emission centers from the outer environment and cut off the energy transfer access between the emission centers and the surface quenching centers, which could reduce the degree of surface quenching and raise luminescent efficiency of nano-materials. A lot of research works revolve around optimizing the thickness of the shell, and then the ions'diffusion in the core-shell nano-materials was discovered. If the doped ions diffuse through the shell from the core of nanoparticles (NPs) to the surface, surface effects and surface quenching will reproduce and the protective effect of the shell would be meaningless. Thus, ions'diffusion might significantly influence the luminescent properties of core-shell nano-materials. It is quite necessary to study and find out the doped ions would diffuse at what temperature to what extent and how it will influence luminescent properties of core-shell nano-materials. My research mainly includes the following three parts:1. Synthesize YVO4:Eu3+NPs and YVO4:Eu3+@YVO4core-shell NPs with different shell thickness by co-precipitation method. Characterize the prepared nano-materials' phase, morphology, size and luminescent properties by X-ray diffraction, transmission electron microscopy, and photoluminescence spectrum. Verify the influence of shell thickness on luminescent properties of core-shell NPs.2. Heat-treat the YVO4:Eu3+@YVO4core-shell NPs under certain protective conditions. Make sure that the Eu3+diffuse outward without NPs'aggregation. Characterize Eu3+'s diffusion extent of different heat-treatment stages by photoluminescence spectrum, photoluminescence decay and fitting method.3. Simulate the diffusion process and luminescence decay of the YVO4:Eu3+@YVO4core-shell NPs, and compare the simulation result and the actual test data to obtain the parameters of the diffusion process.These studies will give a direct impression of Eu3+diffusion in YVO4: Eu3+@YVO4core-shell NPs and help understanding the surface effect and concentration effect. The acquired data should be reference to preparation and application of other core-shell structure of nano-materials. It also provides new options to design and synthesize high luminescent efficiency core-shell nano-materials at elevated temperatures.If the core-shell NPs can be annealed at high temperature without aggregation, then it is possible to optimize luminescent efficiency from three aspects:1. Improve the crystallinity of nano-materials at elevated temperature;2. Prevent surface quenching by controlling the ions'diffusion in a located range.3. Prevent concentration quenching by delicately design the doping concentration in the core and the diffusion extent.