Valence and Site Engineering Enable Efficient Broadband Near-Infrared Emission at 960 nm in Cr³⁺-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 Cr³⁺-activated forsterite (Mg₂SiO₄:1.5%Cr³⁺, 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 Cr⁴⁺ formation but also enhances the cross section of Cr³⁺ d-d forbidden transitions in Mg₂SiO₄. More importantly, Li⁺ promotes excited-state energy transfer between Cr³⁺ 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.