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 (⁴F_9/2→⁶H_13/2) and comparatively weak blue (⁴F_9/2→⁶H_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 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). - Highlights: • Dy³⁺ and Dy³⁺/Tm³⁺:NGW phosphors were synthesised by sol–gel methods. • The excitation spectrum confirmed the strong absorption in near-UV region. • The emission spectrum shows the yellow and white emission to doped and co-doped phosphors respectively. • The CIE co-ordinate conforms close to daylight emission