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

A series of orange-red phosphors NaGd1-x(MoO4)(WO4):xSm(3+) (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 I4(1)/a. Upon excitation at 406 nm, the emission peaks at 564 nm ((4)G(5/2)-> H-6(5/2)), 600 nm ((4)G(5/2)-> H-6(7/2)), 646 nm ((4)G(5/2)-> H-6(9/2)) and 700 nm ((4)G(5/2)-> H-6(11/2)) transitions of Sm3+ were observed. The optimum doping concentration of Sm3+ ions in NaGd1-x(MoO4)(WO4):xSm(3+) 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 angstrom. Compared with NaGd0.97(MoO4)(2):0.03Sm(3+), the fluorescence thermal quenching temperature of NaGd0.97(MoO4)(WO4):0.03Sm(3+) 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.