Suppressing oxygen vacancies and boosting Fe3+ near-infrared emission via charge compensation

The development of efficient, environmentally friendly, and ecologically benign near-infrared (NIR) phosphors is crucial for advancing NIR applications. Although Fe 3+ -doped phosphors are promising candidates, their practical application is often hindered by low luminescence efficiency and severe thermal quenching, which are primarily caused by valence state instability associated with oxygen vacancies. Herein, a strategy of Li + co-doping significantly enhances the performance of Fe 3+ -activated Zn 2 GeO 4 NIR phosphors has been developed. Results demonstrate that Li + co-doping effectively modulates the Fe valence state, suppresses the formation of charge-compensating oxygen vacancies, and promotes the incorporation of Fe 3+ into tetrahedral lattice sites as efficient luminescent centers. Consequently, the optimized Li 0.1 Zn 1.9 GeO 4 : 0.9% Fe 3+ phosphor exhibits a remarkable 26 times enhancement in emission intensity at 770 nm, with a quantum yield surge from 2% to 53% and superior thermal stability (58%@423 K compared to 6% for the undoped sample). A NIR phosphor-converted LED fabricated with the optimal phosphor demonstrates great potential in night vision, biomedical imaging, non-destructive testing, and covert imaging. This work provides a viable charge compensation strategy for engineering high-performance, eco-friendly NIR phosphors. • Li + co-doping boosts Fe 3+ NIR phosphor emission by 26 times. • Thermal stability at 423 K improved from 6% to 58% after Li + co-doping. • Li + co-doping can suppress the formation of oxygen vacancies and Fe 2+ .