Investigation Of Luminescence In Rare-Earth Ions Doped Monophasic Zircon-Type Tetragonal Nanocrystalline LnVO₄-BiVO₄ Solid-Solution

The preparation, characterization and application of rare doped the complete solid-solution of LnVO4-BiVO4 with monophasic zircon-type structure were discussed in this thesis. The research on the materials consists of two parts:the first is down-conversion materials, the second is up-conversion materials. By combining the methods of co-precipitation and hydrothermal synthesis methods, the complete solid-solution of LnVO4-BiVO4 with monophasic zircon-type structure was successfully synthesized in this thesis. The solid-solution properties of were studied by CASTEP of MS-5.5 software under PWPP based on density function theory. The structure and emission spectra excited by near violet light and visible light were investigated. The experimental and theoretic results were helpful to providing useful experimental basis and theoretical basis in red phosphor, white LED and the near infrared to ultraviolet light up-conversion application research.Eu3+, Dy3+, Yb3+ and Tm3+, Er3+ ions are most important fluorescent photoactive for down-conversion (Stocks) and up-conversion (anti-Stocks), respectively. Because they exhibiet excellent luminescent properties, and have significant interaction between the host material and luminescent properties, which may explore the relationship between host structure and properties of RE luminescent. Based on Eu3+, Dy3+, Yb3+ and Tm3+, Er3+ doped LnVO4-BiVO4, we have preformed systematic investigations on light-matter interaction through synthesis, crystals structural and ions doping. Through detailed theoretical analysis, the innovative results have been achieved. The main contents are listed as follows:The results of XRD, TEM and Raman characterization indicate that the crystalline structure of all samples is monophasic zircon-type structure. There was no phase transition occurred due to the increase of the rare earth content from 0 to 1. The formation of solid solution, the excitation have two regions:one is assigned to the VO43- at about 200-400nm, and the other is assigned to the intra-4f transitions of doped rare earth ions at 400-500 nm, enhances the range of visible light.The emission spectra of these EuxBi1-xVO4 and GdxBi0.95-xVO4:0.05Eu3+ phosphors excited at 340 nm and 466 nm exhibited a series of sharp peaks from 400 to 700 nm with. The red emission (5Do â†' 7F2) was observed to change with increase of x. The emission spectra of YxBi0.95-xVO4:0.05Dy3+ has two groups of emissions located at 483 nm (blue light,4F9/2â†' 6H15/2) and 574 nm (yellow light,4F9/2â†' 6H13/2). The tow colors make white light. The effect of Y3+ concentration on the emission intensity was investigated. The color coordinates (CIE) analysis was located at near white color region. The first-principles calculations and diffuse reflectance spectra indicated that the solid-solution resulted in forming impurity energy level. The excitation spectra shows that it has excellent broadband NUV-exciting ability, which due to the electronic transitions from the valence band to conduction band, and indicated that the solid-solution emissions can be achieved via an efficient ET process. The impurity energy level indicated that the Eu3+ and Dy3+ emissions can be achieved via an efficient ET process from the host material to Eu3+ and Dy3+.Up-conversion emission in oxide nanocrystals were investigated. Doping Yb3+ produce an sensitization were designed in BiVO4 nanocrystals. Were first reported on the synthesis of the tetragonal BiVO4 nanocrystals exhibit good thermal stabilities and are highly efficient in UC luminescence. For example, in Yb3+/Er3+ -doped BiVO4 nanocrystals, the main emission peak is the green emission band. In the Yb3+/Tm3+-doped BiVO4 nanocrystals, the strong NIR emission band had observed. Doping high concentration of Yb3+ ions enhance UV up-conersion emission Yb3+/Tm3+-doped BiVO4 nanocrystals. Pump power dependence investigations indicate that they from single photon processes, which can be well explained by using the proposed up-conversion mechanisms.