Sm3+ -activated KLa(WO4)2 phosphors with Gd3+ Co-doping: Orange-Red emission and thermal stability toward potential plant lighting applications

Orange-red KLa(WO 4 ) 2 phosphors co-doped with Sm 3+ -Gd 3+ were synthesized via high-temperature solid-state reaction. Phase purity and crystal structure were confirmed by XRD, while SEM revealed non-uniform particle distribution. XPS verified elemental composition and suggested the chemical states of dopants. Under 403 nm excitation, KLa(WO 4 ) 2 : Sm 3+ exhibited intense orange–red emissions, dominated by the 4 G 5/2 - 6 Hᵢ (i = 5/2, 7/2, 9/2, 11/2) transition from 500 to 750 nm. Substitution by Gd 3+ lowers the local symmetry, as evidenced by the increased asymmetry ratio, resulting in a 1.88-fold increase in emission intensity. Notably, the optimized phosphor, KLa 0.8 Gd 0.15 (WO 4 ) 2 :0.05Sm 3+ , exhibits a high color purity (CP) of 99 % and excellent thermal stability retaining 85 % of its room-temperature emission intensity at 423K. When combined with a 405 nm InGaN chip, the fabricated LED displayed strong spectral overlap with chlorophyll and phytochrome absorption peaks, confirming its potential for plant-growth illumination.