Valence and Site Engineering Enable Efficient Broadband Near‐Infrared Emission at 960 nm in Cr ³⁺ ‐Activated Forsterite

Abstract Near‐infrared (NIR) light sources hold great potential for applications in night vision illumination, bio‐imaging, and non‐destructive testing. However, radiationless de‐activation and low absorption restrict the development of high‐efficiency blue light excitable NIR phosphors, especially for emissions beyond 900 nm. Herein we report a high‐performance Cr ³⁺ ‐activated forsterite (Mg ₂ SiO ₄ :1.5%Cr ³⁺ , 5%Li ⁺ ) phosphor exhibiting broadband NIR emission peaking at 960 nm with a record external quantum efficiency (EQE) up to 48%. The introduction of Li ⁺ as a charge compensator and symmetry distorter not only suppresses Cr ⁴⁺ formation but also enhances the cross section of Cr ³⁺ d ‐ d forbidden transitions in Mg ₂ SiO ₄ . More importantly, Li ⁺ promotes excited‐state energy transfer between Cr ³⁺ emitters, yielding exceptional thermal stability and external quantum efficiency. A fabricated NIR phosphor‐converted light‐emitting diode (LED) achieved a NIR radiated power of 356 mW (at a driving current of 700 mA) and an electro‐optical conversion efficiency up to 12.9% (at 100 mA). This work unlocks new possibilities for smart spectroscopy applications, from non‐destructive testing to human angiography and biometric recognition.