The Synthesis And Photoluminescence Propertie Of Silica And Alumina Based Phosphors

This paper is aimed at improving the luminescent intensity and temperature stability of the phosphor by means of rare earth ions doped, cationic exchange and incorporation of N3- ions. The main results obtained are listed as follow:(1) La3+ doping Li2Sr0.995-xSiO4:0.005Eu2+ were prepared through high-temperature solid-state reaction method under reducing atmosphere. Crystal structures,luminescence properties and fluorescent lifetimes as well as diffuse reflection spectra were characterized by X-ray diffraction, fluorescence spectrophotometer and UV-visible light spectrophotometer. XRD patterns revealed that the samples were single phase of Li2SrSiO4 compounds. The excitation spectrum of all samples showed wide excitation band with the strongest peak at 408 nm. Under the excitation of 408 nm, typical band emission spectrum with single peak at about 570 nm can be achieved, which was attribute to the energy level transition of Eu2+(4f65d1â†'4f7). The complex defects in the host lattice caused by doping La3+ can absorb some energy and then transfer them to Eu2+, which is considered to be the mechanism that significantly enhance the luminous intensity of Li2Sr0.995SiO4:0.005Eu2+ phosphor.(2) A series of Si4+ doping Y2.9Ce0.1Al5-xSixO12 phosphors were prepared by solid-state reaction in 95%N2-5%H2 reduced air ambience. XPS results further revealed that the addition of Si3N4 can promote the reduction degree of Ce4+ ions to Ce3+ ions. Meanwhile, the average decay times of the phosphors are prolonged from 44.8 ns(x=0) and 76 ns(x=0.3). The thermoluminescence properties suggested that the thermal stability of YAG phosphors by Si3N4 doping is well improved compared with undoing phosphors.(3) Si3N4 modified Li2Sr0.995SiO4:0.005Eu2+(Li2Sr0.995SiO4-3x/2Nx:0.005Eu2+) phosphors powder was synthesized with the conventional solid-state reaction in the reduced atmosphere. The crystal structure and vibrational modes are analyzed by X-ray diffraction, Raman scattering spectroscopy and Rietveld crystal structure refinement. Photoluminescence(PL) and photoluminescence excitation(PLE) spectra showed that Li2Sr0.995SiO4-3x/2Nx:0.005Eu2+ powder exhibited a broad yellow emission band centered at 560 nm under the excitation of 460 nm visible light, due to the 4f65d1â†'4f7 transition of Eu2+. The partial nitridation of Li2Sr0.995SiO4-3x/2Nx:0.005Eu2+(x=0.01) phosphors led to a large enhancement in the luminescence intensity. The temperature quenching characteristics and the thermal activation energy calculation results confirmed that the oxynitride based Li2Sr0.995SiO4-3x/2Nx:0.005Eu2+ showed slightly higher stability. At the same time, the fluorescence decay behavior curves further showed that the photoluminescence efficiencies of Li2Sr0.995SiO4-3x/2Nx:0.005Eu2+ phosphors were enhanced by addition of Si3N4.(4) A series of Si3N4 doping M1.99SiO4:0.01Eu2+(M=Sr, Ba) phosphors were prepared by solid-state reaction in 95%N2-5%H2 reduced air ambience. The XRD characteristics plus Rietveld structure refinement analysis revealed that the nitrogen atoms could be incorporated into the host lattice of M2SiO4 through partial occupation of the oxygen atoms sites to form M1.99SiO4-3x/2Nx:0.01Eu2+(M=Sr, Ba). The excitation and emission spectra of M1.99SiO4-3x/2Nx:0.01Eu2+(M=Sr, Ba) phosphors were characterized in detailed as well as the diffuse reflection spectra. It is found that the doped N3- could increase the excited state energy of Eu2+ luminescent centers and enhance luminescence intensity。Emission spectra of Sr1.99SiO4-3x/2Nx:0.01Eu2+ phosphors took on a slight red shift, contrary to that of Sr1.99SiO4:0.01Eu2+. By comparing the fluorescence decay behavior of N3- doping M1.99SiO4:0.01Eu2+(M=Sr, Ba) phosphors with those of undoping, it is found that adding appropriate amounts of Si3N4 into M1.99SiO4:0.01Eu2+(M=Sr, Ba) phosphors are beneficial to further improve the luminescence intensity.