A series of Sr3Y(PO4)3:Eu2+ samples are synthesized by the high temperature solid-state method. Sr3Y(PO4)3:Eu2+shows an asymmetrical emission band under excitation of 350 nm. The emission peaks at 426 nm and 497 nm are assigned to the nine-coordination Eu2+ and six-coordination Eu2+, respectively. The effects of Eu2+ doping content on the emission intensity and color are observed, and the concentration quenching effect is also observed. For two different Eu2+ luminescence centers, the quenching mechanisms are dipole-dipole interaction and quadrupole-quadrupole interaction, respectively. And the critical distance of energy transfer is calculated by concentration quenching and turns out to be about 3.67 nm. The results above show that the asymmetrical emission band of Sr3Y(PO4)3:Eu2+ comes from two different Eu2+ luminescence centers in the lattice.
A series of Tb3+ doped Na Y(Mo O4)2 are synthesized by a solid-state reaction at 550 °C for 4 h, and their luminescent properties are investigated. The phase formation is carried out with X-ray powder diffraction analysis, and there is no other crystalline phase except Na Y(Mo O4)2. Na Y(Mo O4)2:Tb3+ can produce the green emission under 290 nm radiation excitation, and the luminescence emission peak at 545 nm corresponds to the 5D4→7F5 transition of Tb3+. The emission intensity of Tb3+ in Na Y(Mo O4)2 is enhanced with the increase of Tb3+ concentration, and there is no concentration quenching effect. The phenomena are proved by the decay curves of Tb3+. Moreover, the Commission International de I'Eclairage(CIE) chromaticity coordinates of Na Y(Mo O4)2:Tb3+ locate in the green region.
A blue phosphor was obtained by doping Eu^(2+)into a multi-cation host Sr_(0.8)Ca_(0.2)Al_2Si_2O_8 through high temperature solid state reaction.The emission spectra show a continuous red-shift behavior from 413 nm to 435 nm with Eu^(2+)concentration increasing.The substitution priority of Eu^(2+)in Sr_(0.8)Ca_(0.2)Al_2Si_2O_8 was investigated via x-ray diffraction(XRD)and temperature properties in detail:the Ca^(2+)ions are preferentially substituted by Eu^(2+)at lower doping,and with the Eu^(2+)concentration increasing,the probability of substitution for Sr^(2+)is greater than that of replacing Ca^(2+).Accordingly,we propose the underlying method of thermal property to determine the substitution of Eu^(2+)in the multi-cation hosts.Moreover,the abnormal increase of emission intensity with increasing temperature was studied by the thermoluminescence spectra.The energy transfer mechanism between the Eu^(2+)ions occupying different cation sites was studied by the lifetime decay curves.A series of warm white light emitting diodes were successfully fabricated using the blue phosphors Sr^+_(0.8)Ca_(0.2)Al_2Si_2O_8:Eu^2 with commercial red phosphor (CaSr)SiAlN_3:Eu^(2+)and green phosphor(Y Lu)_3Al_5O_(12):Ce^(3+),and the luminescent efficiency can reach 45 lm/W.
