High‐Performance Tunable Near‐Infrared Emitters of Cr3+‐Activated Garnet Phosphor Enabled by Chemical Unit Co‐Substitution

The escalating demand for portable near‐infrared (NIR) light sources has posed a formidable challenge to the development of NIR phosphors characterized by high efficiency and exceptional thermal stability. Taking inspiration from the chemical unit co‐substitution strategy, high‐performance tunable (Lu3‐xCax)(Ga5‐xGex)O12:6%Cr3+ (x = 0–3) phosphors are designed with an emission center from 704 to 780 nm and a broadest full width at half maximum (FWHM) of up to 172 nm by introducing Ca2+ and Ge4+ ions into the garnet structure. In particular, Lu3Ga5O12:6%Cr3+ demonstrates an anti‐thermal quenching phenomenon (I423K = 113.1%). Compared to Lu3Ga5O12:6%Cr3+, Lu2CaGa4GeO12:6%Cr3+ exhibits significantly improved FWHM and IQE by 108 nm and 25.5%, respectively, while maintaining good thermal stability (I423K = 80.4%). Finally, Lu2CaGa4GeO12:6%Cr3+ phosphor is combined with a 465 nm blue LED chip to fabricate NIR LED devices, exhibiting a NIR electroluminescence efficiency of 13.31%@100 mA and demonstrating successful applications in nocturnal illumination and biomedical imaging technology. This work offers a fresh perspective on the design of highly efficient NIR garnet phosphors. Through a chemical unit co‐substitution strategy, the narowband‐emitting Lu3Ga5O12:6%Cr3+ is transformed into a broadband‐emitting Lu2CaGa4GeO12:6%Cr3+. Simultaneously, the internal quantum efficiency is increased to 80.7% while maintaining good thermal stability (I423 K = 80.4%). Ultimately, a prototype NIR pc‐LED with Lu2CaGa4GeO12:6%Cr3+ is fabricated and exhibited superior electro‐optical conversion efficiency (13.31%@100 mA).