Defect engineering via Li+ co-doping for enhanced afterglow in Eu2+-activated Sr2MgSi2O7 phosphors: oxygen vacancy modulation and trap optimization

This study employs an integrated experimental-theoretical approach to systematically investigate Li + co-doping effects in Eu 2+ -activated Sr 2 MgSi 2 O 7 phosphors. Combined X-ray Photoelectron Spectroscopy (XPS) analysis, Electron Paramagnetic Resonance (EPR) characterization, and Density Functional Theory (DFT) calculations experimentally and theoretically confirm that Li + doping effectively induces oxygen vacancy formation, thereby significantly enhancing afterglow performance. Computational results demonstrate that Li + doping increases electron density near the Fermi level by 2.5-fold, substantially improving oxygen's electron delocalization capability. Simultaneously, it reduces oxygen vacancy formation energy from –3.6 eV to –4.0 eV, confirming Li + 's role in facilitating vacancy formation. Experimental measurements reveal that the 0.015 Li + -doped sample exhibits 1.67-fold stronger Eu 2+ characteristic emission at 470 nm compared to undoped counterparts, demonstrating optimal luminescence. Further EPR and thermoluminescence analyses indicate this optimal doping concentration doubles oxygen vacancy defects, creating suitable carrier trap energy levels. Consequently, the optimized phosphor shows 2-fold enhancements in both afterglow decay constant and thermoluminescence intensity, validating significant afterglow improvement through optimized trap distribution. These findings provide critical insights for defect engineering strategies in developing high-performance blue long-afterglow materials.