Synthesis And Luminescence Properties Of SiO₂@(Zn, Sr)₂ SiO₄: Re³⁺ (Re=Eu, Dy) Materials

With the rapid development of rare earth nano-composites, the core-shell structure of rare earth nano-materials has become the study focus of the fluorescent material in recent years. By precise control of experimental conditions, people can synthesis core-shell luminescent and functional materials with special morphology and size according to specific needs. These core-shell luminescent materials not only retain the luminescent properties of original fluorescent materials, but also own spherical shape morphology and independent luminescent centers. In short, the core-shell luminescent materials can be used as a kind of fluorescent and functional material. Therefore, in this paper, the core-shell structure of silicate luminescent materials SiO2@Zn2SiO4:Eu3+and SiO2@Sr2SiO4:Eu3+,Dy3+ had been prepared by sol-gel method. In addition, the coating mechanism, preparation, microstructure, and optical properties of the core-shell structure of the silicate luminescent materials had been studied deeply and systematically.The main contents in this paper are as follows:(1)Regulate and control the morphology and size of Zn2SiO4:Eu3+ particles. With changing the reactant concentration of ammonia, different morphology and size of Zn2SiO4:Eu3+ particles had been prepared by hydrothermal method, in which TEOS was used as silicon source. Furthermore, the reaction conditions were studied and improved by adding an appropriate amount of surfactant (sodium oleate and n-heptane). Finally, the spherical and smaller Zn2SiO4:Eu3+ particles were obtained with a small amount of ZnO impurities in samples. On the basis of this work, the effects of the amount of water on the formation of ZnO impurities were discussed in detail.(2)Determine quenching concentration of Eu3+. The SiO2@Zn2SiO4:Eu3+ core-shell phosphors with uniform coating, smooth shell and controllable thickness were prepared by sol-gel method. Otherwise, the fluorescence lifetime model comprising of fast and slow components was built, which is used to analysis and determine the quenching concentration of Eu3+.(3)Build theoretical models of relationship between the photoluminescence (PL) emission intensities of SiO2@Zn2SiO4:Eu3+, coated layers (N) and particle size (D). According to these models, the effects of coated layers and particle size on the PL intensities were discussed, respectively.(4) Regulate and control the color temperature of SiO2@Sr2SiO4:Eu3+,Dy3+ particles. The results show that the SiO2@Sr2SiO4:Dy3+phosphors emit blue and yellow light under the near ultraviolet (UV) light (386nm) excitation, and the CIE chromaticity coordinate (x, y) cannot be changed by increasing Dy3+ content. On this basis, the CIE chromaticity coordinates (x, y) and color temperatures can be adjusted by introducing Eu3+.(5)Regulate and control the PL emission intensities. The effects of annealing temperature (T) and charge compensation (Li+) on the PL intensities of SiO2@Zn2SiO4:Eu3+and SiO2@Sr2SiO4:Eu3+,Dy3+particles were studied, respectively.