Giant luminescence enhancement in Li2MSiO4:Eu2+ (M = Sr, Ba) via two-step synthesis and charge compensation

Abstract

Eu²⁺-activated phosphors are prominent candidates for next-generation solid-state lighting, but their performance is often limited by incomplete Eu³⁺ reduction and poor thermal stability. Herein, we present a universal strategy combining a two-step synthesis with charge compensation to simultaneously stabilize Eu²⁺ centers and suppress parasitic Eu³⁺. Initially, M₂SiO₄:Eu²⁺ (Pnma) precursors were synthesized to promote effective Eu²⁺ incorporation. Subsequent P⁵⁺ co-doping induces charge-compensated substitution (Si⁴⁺→P⁵⁺). This structural evolution yields the target phosphor phases: the yellow-emitting Li₂SrSi_0.96P_0.04O₄:Eu²⁺ (P3₁21) and the green-emitting Li₂BaSi_0.96P_0.04O₄:Eu²⁺ (P6₃cm) with excitation/emission maxima at 394/580 and 365/520 nm, respectively. Importantly, the heterovalent substitution facilitates the Eu³⁺→Eu²⁺ reduction and optimizes the defect distribution. Consequently, the photoluminescence quantum yield (PLQY) is significantly enhanced from 26% to 78% for Li₂SrSi_0.96P_0.04O₄:Eu²⁺ and from 32% to 83% for Li₂BaSi_0.96P_0.04O₄:Eu²⁺, along with improved thermal stability (93.3%@450 K). Fabricated near-UV pumped white light-emitting diodes (LEDs) incorporating these phosphors demonstrate superior color rendering (Ra = 91.1) and stable electroluminescence across varying currents. The robust Eu²⁺ stabilization and charge compensation paradigm paves the way for rational design of high-performance phosphors for advanced lighting.