UV excitation band induced novel Na3Gd(VO4)2:RE3+ (RE3+ = Eu3+ or Dy3+ or Sm3+) double vanadate phosphors for solid-state lightning applications

Highlights: • Na₃Gd(VO₄)₂ RE³⁺ (RE³⁺ = Eu³⁺ or Dy³⁺ or Sm³⁺) phosphors were prepared by a citrate-based sol-gel method. • Under CTB excitations, Eu³⁺, Dy³⁺ or Sm³⁺ ions activated Na₃Gd(VO₄)₂ phosphors showed red, yellow and orange-red emissions. • The optimized red, yellow and orange-red phosphors exhibited good thermal stability. • The CIE chromaticity coordinate values were calculated for the optimized phosphor samples. The Na₃Gd(VO₄)₂ (NGVO):RE³⁺ (RE³⁺ = Eu³⁺ or Dy³⁺ or Sm³⁺) single doped phosphor materials were synthesized by a citrate-based sol-gel method. The phase formation of NGVO host lattice at different calcination temperatures was analyzed by X-ray diffraction results, which confirmed a monoclinic phase with a space group of P21/c (14). The field-emission scanning electron microscope image of the NGVO sample revealed an agglomerated morphology which was further analyzed by its corresponding energy dispersive X-ray spectrum. Under ultraviolet excitations, the photoluminescence (PL) properties of NGVO:Eu³⁺, NGVO:Dy³⁺ and NGVO:Sm³⁺ phosphors exhibited intense red, yellow and reddish-orange emissions at 618, 575 and 646 nm owing to their characteristic ⁵D₀ → ⁷F₂, ⁴F_9/2 → ⁶H_13/2 and ⁴G_5/2 → ⁶H_9/2 electronic transitions, respectively. The optimum doping concentrations of Eu³⁺, Dy³⁺ and Sm³⁺ ions in the NGVO host lattice were determined to be 0.09, 0.02 and 0.01 mol, respectively. Dexter's theory demonstrates that the quadrupole interactions are responsible for the concentration quenching mechanism in the NGVO:Dy³⁺ and NGVO:Sm³⁺ phosphors. Furthermore, Commission International de I'Eclairage chromaticity diagram was obtained and temperature-dependent PL emission spectra were measured for the optimal NGVO:Eu³⁺, NGVO:Dy³⁺ and NGVO:Sm³⁺ phosphors.