Enhanced photoluminescence properties of Eu3+/Li+ co-doped ZrO2: A focus on red and far-red emissions

In this study, Eu³⁺ and Li⁺ co-doped ZrO₂ nanophosphors were synthesized using a microwave-assisted gel combustion method. While the synthesis method ensures phase stabilization, it does not directly enhance photoluminescence (PL) intensity. Instead, the observed PL enhancement originates from Li⁺ co-doping, which improves charge compensation and modifies local symmetry. Structural analysis confirmed the stabilization of the tetragonal phase due to Li⁺ co-doping, which introduced controlled oxygen vacancies. These structural changes led to a 4.67-fold intensity enhancement in red emission at 611 nm (⁵D₀ → ⁷F₂ transition), and a 4.26-fold increase in far-red emission at 711 nm (⁵D₀ → ⁷F₄ transition). Optimal doping concentrations of Eu³⁺ (0.02) and Li⁺ (0.03) achieved the highest luminescence intensity while maintaining color purity values up to 88.71 %. High-temperature PL measurements revealed stable emission peaks up to 550 K, demonstrating the material’s thermal stability despite intensity reductions due to thermal quenching. These findings establish Eu³⁺/Li⁺ co-doped ZrO₂ nanophosphors as promising candidates for solid-state lighting, plant growth lighting, and optoelectronic applications requiring enhanced red and far-red emissions.