Different Alkali Carbonates on the Microstructure and Photoluminescence Properties of SrWO₄:Tb³⁺ Phosphors

In this research, terbium-doped strontium tungsten oxide samples were synthesized using the solid-state synthesis method. It was found through X-ray powder diffraction (XRD) that the samples belong to the tetragonal crystal system and have the space group I4₁/a. The SEM-EDS images indicate that the Na, K, W, and Tb atoms are uniformly distributed throughout the samples. Photoluminescence (PL) measurements were applied for sample characterization. All of them exhibited green emission with the highest peak at 545 nm attributable to the ⁵D₄ → ⁷F₅ transition. The highest emission intensity was observed in the Sr_0.996Tb_0.004WO₄ sample, while higher doping levels resulted in a decrease in the PL intensities due to concentration quenching. Samples with additional alkali metal ions for charge compensation were also prepared, and their PL properties were measured; the enhancement of co-doping alkali metal (A⁺ = Li⁺, Na⁺, K⁺) on the green luminescence is demonstrated thoroughly. Doping with 0.5 mol% Na⁺ ions yielded a 9.14-fold increase in peak intensity of 545 nm, a 8.02-fold enhancement in operational lifespan, and a 88.82% improvement in quantum yield. These results indicate that Sr_0.991Tb_0.004Na_0.005WO₄ materials have potential application as green phosphors in LEDs.