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 S4 sites of NGW host lattice. In NGW host, under UV excitation the Dy3+ ions have shown strong yellow (4F9/2→6H13/2) and comparatively weak blue (4F9/2→6H15/2) 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 1D2 →3F4 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 (0.333, 0.333).