The Preparation and Optical Properties of Novel LiLa(MoO4)2:Sm3+,Eu3+ Red Phosphor

Abstract

Novel LiLa1−x−y(MoO4)2:xSm3+,yEu3+ (in short: LL1−x−yM:xSm3+,yEu3+) double molybdate red phosphors were synthesized by a solid-state reaction at as low temperature as 610 °C. The optimal doping concentration of Sm3+ in LiLa1−x(MoO4)2:xSm3+ (LL1−xM:xSm3+) phosphor is x = 0.05 and higher concentrations lead to emission quenching by the electric dipole—electric dipole mechanism. In the samples co-doped with Eu3+ ions, the absorption spectrum in the near ultraviolet and blue regions became broader and stronger than these of the Sm3+ single-doped samples. The efficient energy transfer from Sm3+ to Eu3+ was found and the energy transfer efficiency was calculated. Under the excitation at 403 nm, the chromaticity coordinates of LL0.95−yM:0.05Sm3+,yEu3+ approach to the NTSC standard values (0.670, 0.330) continuously with increasing Eu3+ doping concentration. The phosphor exhibits high luminous efficiency under near UV or blue light excitation and remarkable thermal stability. At 150 °C, the integrated emission intensity of the Eu3+ remained 85% of the initial intensity at room temperature and the activation energy is calculated to be 0.254 eV. The addition of the LL0.83M:0.05Sm3+,0.12Eu3+ red phosphors can improve the color purity and reduce the correlated color temperature of WLED lamps. Hence, LL1−x−yM:xSm3+,yEu3+ is a promising WLED red phosphor.

Keywords

• molybdate
• red phosphor
• energy transfer
• thermal stability