Study Of Luminescence Properties Of Phosphors Based On Gallate Salts Hosts Doped With Rare Earth Ion Or Metal Ions

CaGa2O4:Eu3+ reddish phosphor and Si4+ co-doped ZnGa2O4:Cr3+ reddish persistent phosphors have been prepared by the means of high temperature solid state reaction method. The crystalline phase was characterized by the x-ray diffraction meter (XRD) and their optical properties such as photoluminescence, decay and thermoluminescence (TL) were investigated as well. The results of both experiments and analysis are briefly underlined as follows:(1) The rare earth (RE) ions doped CaGa2O4 phosphors with good reddish emission was firstly prepared by the high temperature solid-state reaction, having potential applications to improve the color render index (CRI) and color temperature in white LED lighting. Under the excitation 255 nm light, CaGa2O4:Eu3+ phosphors exhibit two emission bands:A weak emission band with 420～550 nm range attributed to the host emission, and the band of multi-lines sharp emissions, such as 578 nm (5D0-7F0),586 and 597 nm (5D0-7F1),612 and 617 nm (5D0-7F2),655 nm (5D0-7F3) and 702 nm (5D0-7F4), assigned to the characteristic transitions of Eu3+ ions. The strongest 5D0-7F2 emission demonstrated that the doped Eu3+ ions occupied distorted sites without an inversion symmetry center in CaGa2O4 host lattice. The dependence of the emission intensity upon Eu3+ concentration indicates that the optimum doping concentration of Eu3+ is 0.04. The intensity quenching occurs when Eu3+ content over 0.04. The inner energy transfer between the host and the doped RE ions (luminescence center) has been observed by monitoring the characteristic emission of RE ions under the host absorption at 255 nm.(2) ZnGa2O4:Cr3+ phosphors with addition of Si4+ were synthesized by conventional solid-state reaction method. The influence of the co-doped Si4+ ions on both fluorescent and phosphorescent properties of ZnGa2O4:Cr3+ phosphors were investigated by means of photoluminescence (PL) spectrum, luminescence decay curves and thermoluminescence (TL) curves. As observed in photoluminescence (PL) spectra, the relative intensities of N2 line and R lines increase along with the increasing of the anti-site defects due to the co-doped Si4+. According to the fitting of the TL glow curves, the density and depth of Zn vacancies vary with different Si4+ contents: the sample with Si4+ at 0.01 reaches the optimal persistent performance as it possesses the most amount of Zn vacancies. By comparing to the previous results, it was proposed that the Zn vacancies gradually rise with the increasing Si4+ dopant, then up to a maximum value, and finally descend at larger Si4+ content. In addition, Si4+ might preferentially occupy the Zn vacancies and sequentially fill into the Ga3+ sites, producing the substitution of Zn2+ by Ga3+.