Luminescent properties of orange-red emitting phosphors NaGd(MoO4)(WO4):Sm3+ for white LED

Abstract A series of orange-red phosphors NaGd1-x(MoO4)(WO4):xSm3+ (x = 0.01, x = 0.02, x = 0.03, x = 0.04, x = 0.05 and x = 0.06) were prepared by a high temperature solid state reaction in air atmosphere. X-ray diffraction, photoluminescence (PL) spectra and fluorescent thermal stability analysis were utilized to characterize the structure and luminescence properties of as-prepared phosphors. The chromaticity coordinates of the samples were calculated and located in the orange-red region. These phosphors possessed scheelite tetragonal crystal structure with a space group of I41/a. Upon excitation at 406 nm, the emission peaks at 564 nm (4G5/2 → 6H5/2), 600 nm (4G5/2 → 6H7/2), 646 nm (4G5/2 → 6H9/2) and 700 nm (4G5/2 → 6H11/2) transitions of Sm3+ were observed. The optimum doping concentration of Sm3+ ions in NaGd1-x(MoO4)(WO4):xSm3+ was x = 0.03. The energy transfer mechanism between the Sm3+ ions was confirmed as dipole–dipole interaction and the critical distance was obtained to be 21.59 A. Compared with NaGd0.97(MoO4)2:0.03Sm3+, the fluorescence thermal quenching temperature of NaGd0.97(MoO4)(WO4):0.03Sm3+ increases from 398 K to 473 K, which preformed higher thermal stability and emitting-color stability, and shows a great potential for its application in LEDs as a suitable orange-red-emitting phosphor.