Luminescence enhancement and thermal stability of alkali co-doped Eu3+:LaMgB5O10 phosphors.

Eu³⁺-activated LaMgB₅O₁₀ (LMBO:Eu³⁺) phosphors were synthesized and systematically investigated to elucidate the role of alkali co-doping (Li⁺, K⁺) on their structural and luminescence properties. XRD, Raman, and FTIR analyses confirmed the phase purity and revealed subtle lattice distortions upon alkali incorporation, while SEM/EDS verified homogeneous dopant distribution. Photoluminescence spectra are dominated by the characteristic ⁵D₀→⁷FJ transitions of Eu³⁺, with alkali ions inducing pronounced modifications in band distribution and emission intensity. Li⁺ co-doping yields a moderate enhancement and redistributes oscillator strength toward the ⁵D₀→⁷F₄ transition, whereas K⁺ co-doping produces nearly an order of magnitude increase in far-red emission. Judd-Ofelt analysis provided intensity parameters (Ω₂, Ω₄, Ω₆), radiative lifetimes, and quantum efficiencies, highlighting the impact of alkali-induced site symmetry perturbations. Temperature-dependent PL measurements revealed distinct quenching and anti-thermal quenching (ATQ) behaviors: undoped Eu³⁺ exhibited conventional quenching with an activation energy of 0.404 eV, K⁺ co-doping reduced the barrier to 0.205 eV and triggered moderate ATQ above 470 K, while Li⁺ co-doping produced strong ATQ with emission intensity increasing nearly fourfold at 550 K. These findings demonstrate that alkali co-doping not only enhances far-red emission at room temperature but also stabilizes or even amplifies luminescence at elevated temperatures, making LMBO:Eu³⁺,M⁺ phosphors promising candidates for high-power pc-WLEDs and plant-growth lighting.