Sol-gel synthesis and photoluminescence studies on colour tuneable Dy3+/Tm3+ co-doped NaGd(WO4)2 phosphor for white light emission

A series of Dy3+/Tm3+ ion co-doped NaGd(WO4)(2) (NGW) phosphors were synthesised by a sol-gel method at low temperature for white light emission. The structural and luminescence properties of the synthesised phosphors were studied by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman and photoluminescence techniques. In Dy3+/Tm3+:NGW phosphors, the dopant ions substituted Gd3+ ions that are located in S-4 sites of NGW host lattice. In NGW host, under UV excitation the Dy3+ ions have shown strong yellow (F-4(9/2) --> H-6(13/2)) and comparatively weak blue (F-4(9/2) --> H-6(15/2)) emission transitions at 575 and 488 nm, respectively. Due to deficient blue colour the overall emission falls in yellow region. Hence, Tm3+ ions having strong blue emission at 455 nm corresponding to the transition D-1(2) --> F-3(4) were co-activated along with Dy3+ ions in NGW matrix. BY changing the doping concentrations of Tm3+ and Dy3+ ions in NGW, white light emission was tuned by 353 nm excitation wavelength. Their corresponding colour co-ordinates were calculated and found to be very close to the white colour chromaticity co-ordinates (0333, 0333). (C) 2014 Elsevier B.V. All rights reserved.