A Highly Efficient NIR-II-Emitting MgGa2O4:Cr3+,Ni2+ Phosphor via Cr3+ Ions in Tetrahedral Sites as the Cr3+-Ni2+ Energy Transfer Bridge
The Ni2+ ion exhibits broadband near-infrared (NIR) II emission (1000–1700 nm) but suffers from low absorption efficiency and cannot be effectively excited by blue light chips, impeding commercial application. This study introduces Cr3+ sensitizer ions into MgGa2O4:0.01Ni2+, markedly enhancing blue-light absorption and photoluminescence. The optimized MgGa2O4:0.24Cr3+,0.01Ni2+,2 wt% H3BO3 sample exhibits broadband emission from 1000 to 1600 nm with a peak at 1290 nm, achieving internal and external photoluminescence quantum yields of 81.91% and 62.51%, respectively. Comprehensive optical characterization, X-ray absorption near-edge structure spectra, and low-temperature photoluminescence spectra determine that Cr3+ ions occupy tetrahedral sites, and their energy level acts as an intermediate for efficient Cr3+→Ni2+ energy transfer. The packaged NIR phosphor-converted light-emitting diode (pc-LED) demonstrates an electro-optical conversion efficiency of 11.38% at 20 mA and a NIR output power of 52.66 mW at 350 mA, showcasing exceptional performance for NIR-II applications.