Pushing the Limits of Fe ³⁺ Luminescence: An F ⁻ Regulation Strategy for NIR Phosphors With 88% IQE and Anti‐Thermal‐Quenching Behavior

ABSTRACT Near‐infrared (NIR) phosphors find extensive applications in plant growth lighting. Yet, the limited efficiency, poor thermal stability, and match to phytochrome absorption hinder the advancement of plant lighting technologies. Herein, this study successfully developed a novel Fe 3+ ‐doped NIR phosphor, Li 1.5 Al 4 O 5.7 F 2.1 : Fe 3+ , through a dual strategy combining excess LiF regulation and F − substitution for O 2− , achieving an internal quantum efficiency (IQE) of up to 88% and a significant anti‐thermal quenching effect (126.9%@453 K). The introduction of F − not only shifts the emission peak to 730 nm for an optimal match with the absorption of the far‐red phytochrome, but also enhances structural rigidity, reduces electron‐phonon coupling, and repairs oxygen vacancy defects, setting a new performance record (IQE = 88.2% and 126.9%@453 K) for Fe 3+ ‐doped materials. Moreover, the fabricated NIR phosphor‐converted light‐emitting diodes exhibit outstanding operational stability under high drive currents and Cu 2+ quantitative detection, constructing an intelligent plant growth illumination system. Their potential applications in night vision, non‐destructive testing, and bioimaging were also demonstrated. Thus, this work not only provides a high‐performance Fe 3+ ‐activated NIR phosphor for plant growth lighting but also offers a universal strategy for optimizing luminescence properties through anion regulation and defect engineering.