Eu 2+ Doping Concentration‐Driven Site Selectivity Enables Tunable Luminescence in Sr 2 LuTaO 6 for Lighting and Optical Authentication

Eu 2+ ‐activated phosphors are promising for various photonic applications; however, luminescence control and modification are always challenging. In this study, Eu 2+ doping concentration‐driven site‐selective luminescence is realized in monoclinic Sr 2 LuTaO 6 , with oxalic acid enhancing Eu 3+ →Eu 2+ conversion efficiency. Increasing Eu 2+ concentration drives its redistribution from SrO 8 sites to LuO 6 sites, giving rise to green emission at 534 nm under UV excitation and red emission at 612 nm under blue excitation. Eu 2+ at the SrO 8 site exhibits superior thermal stability, retaining 93% of its room‐temperature emission intensity at 150°C, compared with 70.2% for the LuO 6 site, due to its larger thermal activation barrier. These distinct luminescence properties enable the applications of Sr 2 LuTaO 6 :Eu 2+ phosphors in white‐light lighting and optical authentication. This work clearly shows the potential of site‐occupation engineering for the rational design of multifunctional phosphors.