A highly efficient NIR-II-emitting MgGa2O4:Cr3+,Ni2+ phosphor via the Cr3+ ions in tetrahedral sites as the Cr3+-Ni2+ energy transfer bridge

The Ni2+ ion has garnered increasing attention due to its broadband emission in the near infrared (NIR) II region (1000-1700 nm). However, it exhibits low light absorption efficiency and cannot be effectively excited by blue light chips, thereby significantly impeding its commercial application. Herein, we introduced the Cr3+ sensitizer ion into MgGa2O4:0.01Ni(2+), which remarkably enhanced the absorption efficiency of blue light and improved the photoluminescence properties. It is noteworthy that the MgGa2O4:0.24Cr(3+),0.01Ni(2+),2 wt% H3BO3 sample exhibits a broadband emission spanning from 1000 to 1600 nm, with an emission peak at 1290 nm, achieving high internal and external photoluminescence quantum yields of 81.91% and 62.51%, respectively. The occupancy of Cr3+ ions at the lattice sites in MgGa2O4 was comprehensively discussed and analyzed using various optical characterization techniques. Additionally, based on X-ray absorption near-edge structure spectra and low-temperature photoluminescence spectra, it has been determined that the energy level of Cr3+ in tetrahedral sites acts as an intermediate level for energy transfer from Cr3+ to Ni2+, leading to high energy transfer efficiency. The electro-optical conversion efficiency of the packaged NIR phosphor-converted light-emitting diode device reaches 11.38% under a driven current of 20 mA, and the NIR output power can reach up to 52.66 mW at 350 mA, showcasing the exceptional electro-optical properties of the as-fabricated NIR pc-LED within the NIR II range.