Interstitial Solid Solution Design Breaks the Property Ceiling: Cr ³⁺ Doped Near‐Infrared Phosphors with EQE Exceeding 50% and Zero‐Thermal‐Quenching Characteristics

Abstract Ultra‐efficient near‐infrared (NIR) phosphor‐converted light‐emitting diodes are essential for advancing biomedical imaging and nondestructive testing. However, existing Cr ³⁺ ‐doped phosphors encounter challenges such as low external quantum efficiency (EQE) and severe thermal quenching. Herein, we propose an innovative interstitial solid solution strategy by incorporating quadrivalent ions (e.g., Ge ⁴⁺ , Sn ⁴⁺ , Ti ⁴⁺ ) into Cr ³⁺ ‐activated β‐Ga ₂ O ₃ derivatives. The formation of interstitial oxygen ions during this process enhances structural rigidity and relaxes the spin selection rule of Cr ³⁺ by reducing the structural symmetry, as confirmed by first‐principles calculations and extended X‐ray absorption fine structure analysis. The optimized Ga _2–y Sc _y O ₃ :Cr ³⁺ , Ge ⁴⁺ phosphors, with emission tunable from 689 to 780nm, achieve ultra‐high EQEs exceeding 50% and exhibit nearly zero‐thermal‐quenching (ZTQ) characteristics. This is the first report of successfully developing NIR phosphors that simultaneously achieve EQE exceeding 50% and exhibit ZTQ properties. A representative as‐fabricated NIR pc‐LED device demonstrates superior performance, achieving an output power of 67.0 mW and a photoelectric conversion efficiency of 24.5% at 100 mA, surpassing state‐of‐the‐art devices and showcasing immense potential in bioimaging, night vision, and nondestructive testing. This work not only provides high‐performance NIR phosphors but also establishes a pioneering paradigm for designing advanced NIR phosphors via the interstitial solid solution strategy.