Unlocking Cr<sup>3+</sup>–Cr<sup>3+</sup> Coupling in Spinel: Ultrabroadband Near-Infrared Emission beyond 900 nm with High Efficiency and Thermal Stability
Geng Chen, Yahong Jin, Lifang Yuan, Bo Wang, Jiansheng Huo, Hao Suo, Haoyi Wu, Yihua Hu, Feng Wang
Abstract
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 x Zn 1– x Ga 2 O 4 to tune the NIR emissions of Cr 3+ activators. By combining crystal field engineering and heavy doping, the Cr 3+ –Cr 3+ ion pair emission from the 4 T 2 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.