Highly Efficient and Thermally Stable Na₅Lu(WO₄)₄:Sm³⁺ Red-Emitting Phosphors for Near-Ultraviolet-Pumped White Light-Emitting Diodes

Due to the lack of red light, currently available commercial phosphor-converted white light-emitting diodes (pc-WLEDs) have a poor color rendering index. In order to improve the color rendering performance of pc-WLEDs, it is urgent to develop satisfactory bright red emission phosphors. Herein, we reported a bright red luminescent Na5Lu(WO4)4:Sm3+ phosphor. By studying the effect of Sm3+ doping concentration on luminescence performance, it was found that the concentration quenching effect was attributed to the dipole–dipole interaction. The quantum yield, color purity, and CIE coordinates of the optimal Sm3+ concentration activated Na5Lu(WO4)4:9%Sm3+ phosphor were 49.37%, 95.12%, and (0.653, 0.346), respectively. Furthermore, the phosphor had strong resistance to thermal quenching, and the luminous intensity at 425 K was only reduced by 10.20% compared with that at 300 K, while maintaining excellent color stability (Δε = 9.27 × 10–3). Finally, we used Na5Lu(WO4)4:9%Sm3+ phosphor as the red component, and additionally added commercial blue and green phosphors, combined with the 365 nm near-ultraviolet chip to produce a white LED device with a CRI of up to 90.5 and a CCT as low as 4581 K. These results indicated that Na5Lu(WO4)4:Sm3+ phosphors had broad potential applications in high color rendering index white LEDs excited by near-ultraviolet light.