Luminescence And Mechanism Studies Of Rare Earth Eu Ions Activated Antimonite And Silicate Phosphors

Rare-earth（RE） is an enormous fortune for the development of luminescence materials. Rare-earth ions have many advantages, such as abundant element types, unique electronic structure, and stable physical and chemical properties. The luminescence properties of rare earth ions have attracted much attention from scholars at home and abroad, thus promoting the development of inorganic luminescent material. Rare earth ions activated phosphors with all kinds of colors are widely studied, and their excellent luminescent properties are used in lighting, display, laser, and biomedical area. In this paper, the antimonate and silicate matrix were choosed and Eu doped red phosphors and yellow-green phosphors were synthesized respectively. The crystal-phase structure and morphology were verified by X-ray powder diffraction and structural refinements. The luminescence properties such as photoluminescence excitation and emission spectra, fluorescence decay curves, CIE color coordinates, and absolute luminescence quantum efficiency were investigated, and the luminescent transitions fâ†'f of Eu³⁺ and dâ†'f of Eu²⁺ were analysised, the results have shown that these phosphors can have potential applications in the field of inorganic luminescent material.In chapter 3, the red-emitting rare earth antimonates of Eu³⁺-doped R₃SbO₇（R=La, Gd, Y） were prepared by the high-temperature solid-state reaction. The crystal-phase formations were verified by X-ray powder diffraction and structural refinements. The luminescence properties such as photoluminescence excitation and emission spectra, fluorescence decay curves, absolute luminescence quantum efficiency, CIE color coordinates and the dependence of luminescence intensity on doping level were investigated. The luminescence QE, CIE color coordinations, and the spectrum characteristics of Eu³⁺ ions have the strong dependences on both R（La, Gd, Y） cations and Eu³⁺ doping levels. 5D0â†'7F4 emission peak at 710 nm was the dominated transition in Eu³⁺-doped La₃SbO₇, while 5D0â†'7F0 at 580 nm presents the strongest transition intensity in Eu³⁺-doped Y₃SbO₇. The luminescence properties were discussed on the base of the crystal structure. Different Eu³⁺ luminescence centers such as isolated centers, the pair broadening, and cluster centers were discussed on the dependence of the lifetime values on Eu³⁺-concentration. The luminescence QE of La₃SbO₇:0.4Eu³⁺ can reach 63.8% under the excitation of UV light at room temperature. It can have potential application as a red-emitting phosphor for solid-state lighting.In chapter 4, Rare earth Eu²⁺ ions doped halosilicate Ca₁₀Si₆O₂₁Cl₂ was prepared by solid state reaction method. The X-ray powder diffraction patterns, the scanning electron micrographs, the photoluminescence excitation and emission spectra, and the thermal stability were measured. The luminescence properties were investigated by dynamic excitation of a pulsed UV laser. Two typical Eu²⁺ emission centers were suggested from two different Ca²⁺ cation sites in the lattices. With increasing Eu²⁺-doping concentration, the energy transfer between the two Eu²⁺ centers can happen. The emission mechanism was discussed by analyzing the excitation and emission spectra, the concentration-dependent luminescence intensity, and the lifetimes. The colors of Ca₁₀Si₆O₂₁Cl₂:xEu²⁺ change from bluish green to yellowish green by increasing the Eu²⁺-doping concentration. The luminescence stability with temperature was evaluated by the activation energy（ΔE） for thermal quenching.In chapter 5, Eu-activated（x=0.001–0.05） calcium chloride silicate Ca₇Si₂O₈Cl₆:xEu phosphors were prepared by solid state reaction method, which were characterized by X-ray powder diffraction and SEM measurements. The luminescence properties were investigated by the photoluminescence excitation and emission spectra, the luminescence decay lifetimes, the color coordinates and the internal quantum efficiency. Ca₇Si₂O₈Cl₆:xEu contains two kinds of Eu-emission centers, i.e., Eu²⁺ and Eu³⁺ ions, even it was prepared in a reducing atmosphere. Eu²⁺ and Eu³⁺ ions which present the characteristic broad band（5dâ†'4f） and narrow 4fâ†'4f luminescent features, respectively. The luminescence mechanism was discussed by analyzing the spectra, concentration-dependent emission intensity and lifetimes. With increasing Eu-doping, the energy transfer happens from Eu²⁺ to Eu³⁺ centers. Upon an excitation with near UV light, the luminescence color can be tunable from green to orange with increasing the Eu-doping because of the changes of the luminescence components from Eu³⁺ and Eu²⁺ ions in Ca₇Si₂O₈Cl₆ host. This is a potential phosphor combining both luminescence effects of Eu²⁺ and Eu³⁺ ions.Finally, the structural and morphology features, typical luminescence properties of rare earth Eu ions doped antimonate R₃SbO₇:xEu³⁺（R=La, Gd, Y, x=0.05-1.0） red phosphors, silicate Ca₁₀Si₆O₂₁Cl₂:xEu²⁺ green phosphors, and Ca₇Si₂O₈Cl₆:xEu yellow-green phosphors, were systematically studied. Among them, the evolution about crystal phase and luminescence spectra were firstly studied in Eu³⁺ doped antimonate R₃SbO₇:xEu³⁺（R=La, Gd, Y, x=0.05-1.0） phosphors and the craystal phase evolved from Cmcm phase（R=La） to C2221 phase（R=Gd, Y）. In the luminescence spectra of R₃SbO₇:xEu³⁺（R=La, Gd, Y, x=0.05-1.0）, the dominant transitions are different from each other in all kinds of hosts, and the best doping concentration of Eu³⁺ is 40 mol%. The silicate Ca₁₀Si₆O₂₁Cl₂:x Eu²⁺ green phosphors were synthesized through the high temperature solid state method, and investigated their structure features and luminescence properties. There are two different Eu²⁺ luminescence centers. With the increase of Eu²⁺-doping concentration, the emission spectra show a red shift, and the luminescence colors are tunable. The structure features and luminescence properties of silicate Ca₁₀Si₆O₂₁Cl₂:xEu yellow-green phosphors were investigated. There are two independent luminescence centers of Eu²⁺ and Eu³⁺ in the lattice of Ca₇Si₂O₈Cl₆ host. This kind of phosphors has a potential application as a color-tunable emitting material for lighting and display.