Synthesis and luminescence properties of Sm3+ doped Na5Ln(WO4)4 (Ln=Y, La, and Gd ) red phosphor for near UV LED

Abstract

White light-emitting diodes (LEDs) presented many advantages are receiving much attention to be the candidate for new lighting systems in the future. The most common used yttrium aluminum garnet (Ce3+:YAG) phosphor is dominating, however, the lack of red emitting component cannot give rise to high quality true white light. Studies are focusing on the UV-LED with triple-wavelength RGB phosphor to improve the problem recently. Tungstate phosphors, as a new host material, doped with Sm3+ can generate red emission from 4G5/2 level to 6H5/2, 6H7/2 and 6H9/2 respectively. Samarium(III) ions exhibit enhanced luminescence emission owing to excitation energy transfer from groups WO42- to Sm3+ ions in the Na5Ln(WO4)4 salt. The Na5Ln(WO4)4 powder phosphors are prepared by the common solid state reaction method. The well crystallized Na5Ln(WO4)4 powder phosphors were characterized by X-ray diffraction, field emission scanning electron microscopy (FESEM), and photoluminescence (PL) spectra. The crystalline structure of the phosphors were discussed, all the samples obeys the cubic shape tetragonal phase with approximate diameter of 500 nm. All prepared powders have been crystallized in corresponding to the JCPDS card. The PLE and PL spectra of the Na5Ln1-xSmx(WO4)4 powder phosphors are measured and compared with the changing of temperature and rare-earth ion doping concentration. To the aspect of practical application, the CIE chromaticity coordinates values of Sm3+ ion doped Na5Y(WO4)4, Na5La(WO4)4, and Na5Gd(WO4)4 were calculated to be x = 0.65, y = 0.35 in view of their emission spectra.