Interstitial‐Li Induced Oxygen Defect in Self‐Activated BaAl ₂ B ₂ O ₇ for Enhancing Near‐Infrared Luminescence and Thermal Stability

Abstract Self‐activated near‐infrared (NIR) phosphors are promising candidates for advanced NIR light sources due to their intrinsic non‐toxic composition and cost‐effectiveness. However, their practical implementation is hindered by low defect concentration, which critically restricts luminescence efficiency. This study introduces a novel defect engineering strategy via interstitial lithium incorporation in BaAl 2 B 2 O 7 (BAB:Li + ), achieving simultaneous enhancement of NIR emission intensity, spectral modulation, and thermal stability. Structural characterization and density functional theory (DFT) calculations reveal that the broad 780 nm emission under 330 nm excitation originates from interstitial oxygen (O i ) defects in the BAB host. Remarkably, through this interstitial‐Li induced oxygen defect engineering method, BAB:0.10Li + demonstrates an eight‐fold emission intensity increase accompanied by a 72 nm blueshift, compared to the pristine BAB. Thermoluminescence (TL) analysis confirms that the improvement stems from dual key reasons: O i defects concentration and introduction of additional deep traps. The engineered deep traps endow the phosphor with excellent thermal stability, retaining 86% of initial intensity at 150 °C versus 37% for unmodified counterpart. This validates possible applications in night‐vision, biological imaging and fingerprint detection. The defect engineering paradigm probably establishes a general approach for developing high‐performance self‐activated NIR phosphors, opening a new avenue for advanced optical materials design.