Unlocking Cr3+–Cr3+ Coupling in Spinel: Ultrabroadband Near-Infrared Emission beyond 900 nm with High Efficiency and Thermal Stability

Broadband near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) hold promising potential as next-generation compact, portable, and intelligent NIR light sources. Nonetheless, the lack of high-performance broadband NIR phosphors with an emission peak beyond 900 nm has severely hindered the development and widespread application of NIR pc-LEDs. This study presents a strategy for precise control of energy-state coupling in spinel solid solutions composed of Mg_xZn_1-xGa₂O₄ to tune the NIR emissions of Cr³⁺ activators. By combining crystal field engineering and heavy doping, the Cr³⁺-Cr³⁺ ion pair emission from the ⁴T₂ state is unlocked, giving rise to unusual broadband NIR emission spanning 650 and 1400 nm with an emission maximum of 913 nm and a full width at half-maximum (fwhm) of 213 nm. Under an optimal Mg/Zn ratio of 4:1, the sample achieves record-breaking performance, including high internal and external quantum efficiency (IQE = 83.9% and EQE = 35.7%) and excellent thermal stability (I_{423 K}/I_{298 K} = 75.8%). Encapsulating the as-obtained phosphors into prototype pc-LEDs yields an overwhelming NIR output power of 124.2 mW at a driving current of 840 mA and a photoelectric conversion efficiency (PCE) of 10.5% at 30 mA, rendering high performance in NIR imaging applications.