Study On The Synthesis And Luminescent Properties Of Molybdate Red Phosphors

Molybdate materials with scheelite structure have excellent chemical stability and luminescent properties. Due to MoO42- having strong absorption in near UV region and ability of transfering energy to rare earth ions, molybdate materials have a broad charge transfer (CT) band. Therefore, molybdate materials are superior matrix for phosphors.In this paper, rare earth ions Eu3+, Y3+, Sm3+ doped molybdate red phosphors were prepared by sol-gel methods. The crystal structure, particle morphologies and luminescent properties were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), excitation spectrum and emission spectrum. Four groups of schemes were designed as following:Ca1-1.5xMoO4:xEu3+, Cao.5Mo04:0.25Eu3+, 0.25M+(M=Li,Na,K), Ca0.25Y0.5-xMoO4:xEu3+ and Na0.5Y0.3MoO4:(20-x)Eu3+,xSm3+. The doping pattern of Ca1-1.5xMoO4:xEu3+ and Ca0.25Y0.5-xMoO4:xEu3+ phosohors is that two trivalent rare-earth ions substitute three Ca2+ ions to form two EuCa and one VCa". The doping pattern of Ca0.5MoO4:0.25Eu3+,0.25M+(M=Li,Na,K) and Na0.5Y0.3MoO4: (20-x)Eu3+,xSm3+ phosohors is that one trivalent rare-earth ion and one M+ ion replace two Ca2+ ions to form one EuCa and one MCa’.The XRD analysis shows four groups of the samples are all pure CaMoO4 phases, and no other phase appears, revealing that doping ions can enter molybdate crystal to subsitute Ca2+ ions.The CT bands of the four groups of samples locate 200-350nm in excitation spectra. Excitation peaks among 200～350nm were the direct excitation of f-f. The excitation centers of the four groups of samples at 364nm,386nm,396nm,419 run and 466nm. Characteristic peak locates at 396nm (7F0â†'5L6 transition). Moreover, Na0.5Y0.3MoO4: (20-x)Eu3+,xSm3+ samples have 6H5/2â†'4K11/2 transition at 408nm, corresponding to absorption of Sm3+ in the near ultraviolet region.Four groups of the samples all have four emission peaks in emission spectra at 596nm,616nm,656nm and 704nm. Characteristic peak locates at 616nm (5D0â†'F2 transition). The optimal doping concentration of Eu3+ was 25mol% in Ca1-1.5xMoO4: xEu3+. The effect of Li+ on the promotion extent for luminescent intensity was largest in Ca0.5MoO4:0.25Eu3+,0.25M+(M=Li,Na,K). The optimal doping concentration of Eu3+ was 20mol% in Ca0.25Y0.5-xMoO4:xEu3+. The optimal doping concentration of Sm3+ was 3mol% in Na0.5Y0.3MoO4:(20-x)Eu3+,xSm3+.The color purity of the samples improves with the increasing of Eu3+ molar content in Ca1-1.5xMoO4:xEu3+. The color purity of the sample with Li+ doping is highest among Ca0.5MoO4:0.25Eu3+,0.25M+ (M=Li,Na,K). The color purity of the samples improves with the increasing of Eu3+ molar content in Ca0.25Y0.5-xMoO4:xEu3+. The color purity of the samples improves with the decreasing of Eu3+ molar content in Na0.5Y0.3MoO4:(20-x)Eu3+,xSm3+.