Preparation And Luminescence Properties Of Rare Earth Doped Phosphors

Silicate phosphors are widely used in lighting device due to their stable physicaland chemical property. Meanwhile, the photoluminescence (PL) andphotoluminescence excitation (PLE) spectra of tungstate phosphors are not easilyaffected by other factors and the characteristic absorption band has a large scopecovering almost the visible light range, all making the phosphors get more and moreattention. In the paper, the luminescence properties, energy transfer between certainrare earths and charge compensation about the phosphors were studied. The mainobtained results were as following:1. Solid solution Ca1.855Si0.71P0.29O4was obtained according to theCa2SiO4-Ca3(PO4)2phase diagram. With this solid solution as the host,Ca1.855Si0.71P0.29O4: Eu2+phosphors were made using the solid state technique. Eu2+doping is benefit for the stability of the solid solution. Luminescence properties ofCa1.855Si0.71P0.29O4: Eu2+phosphors were discussed and the mechanism of energytransfer between Eu2+was energy transfer among the nearest neighbor ions. Theasymmetrical PLE spectra of Eu2+as well as the fitting fluorescent decay results showthe existence of two Eu2+sites.2. CaWO4: Dy3+, Eu3+phosphors were prepared by the high temperature solidstate reaction. Luminescence properties of CaWO4: Dy3+，CaWO4: Eu3+and CaWO4:Dy3+, Eu3+were discussed. First the optimum doping concentration of Dy3+wasdefined, and then Eu3+was co-doped successfully. PL and PLE spectra of CaWO4:Dy3+, Eu3+indicated both the characteristic spectra of Dy3+and Eu3+. Results provedthe energy transfer between Dy3+and Eu3+.3. CaWO4: Sm3+phosphors were successfully synthesized. As we know, thesubstitution of Ca2+by Sm3+was charge unbalanced, and three approaches to chargecompensation were investigated in order to reduce the influence on the luminousintensity in the work. First,3Ca2+→2Sm3++vacancy, that is, three Ca2+ions arereplaced by two Sm3+ions to balance the charge. Secondly,2Ca2+→Sm3++M+,where M+is a monovalent ion like Li+, Na+, K+. Thirdly, Ca2+→Sm3++N-, where N- is a monovalent ion like F-, Cl-, Br-, I-. Results demonstrated that the first two wayscan improve the luminous intensity.