Structural and luminescence analysis of Li+/Na+ co-doped K7 CaGd2 (B5 O10)3:Tb3+ phosphors with enhanced green emission and thermal stability

Abstract

Li⁺/Na⁺ co-doped K7CaGd2(B5O10)3:Tb3+ (KCGBO) green phosphors were synthesized via a microwave-assisted combustion method. XRD confirmed a pure rhombohedral phase (R32). Under 378 nm excitation, strong green emission at ~544 nm (⁵D₄→⁷F₅) was observed, optimized at 3 wt% Tb³⁺ before quenching. Li⁺/Na⁺ codoping enhanced luminescence through local field distortion and improved energy transfer. Judd–Ofelt anal ysis revealed superior radiative efficiency for Li⁺ co-doped samples (AJ = 1.12 × 10⁶ s⁻¹, τrad= 0.089 ms, G = 1.08 × 10–22 cm²). Thermal studies showed 82% intensity retention at 450 K with partial anti-thermal quenching and activation energy of ~0.52 eV, indicating suppressed non-radiative losses. The results demonstrate that Li⁺/Na⁺ co-doping and optimized Tb³⁺ content synergistically improve emission efficiency and thermal stability, making KCGBO:Tb³⁺ a promising green phosphor for near-UV solid-state lighting.