Valence and Site Engineering Enable Efficient Broadband Near-Infrared Emission at 960 nm in Cr3+-Activated Forsterite

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.