A Highly Efficient NIR-II-Emitting MgGa2O4:Cr3+,Ni2+ Phosphor via Cr3+ Ions in Tetrahedral Sites as the Cr3+-Ni2+ Energy Transfer Bridge

• • Internal photoluminescence quantum yield (PL QY) of 81.91% and external PL QY of 62.51% at an emission peak of 1290 nm, with a broad full width at half maximum spanning 1000–1600 nm. This addresses the scarcity of high-efficiency NIR-II phosphors excitable by blue light, enabling compact, high-brightness pc-LEDs for biomedical imaging and food quality assessment. • • Electro-optical conversion efficiency of 11.38% under a driven current of 20 mA in a packaged NIR pc-LED device. This metric directly impacts energy savings and thermal management in portable NIR spectroscopy systems, where low efficiency has historically limited battery life and signal-to-noise ratios. • • NIR output power reaching 52.66 mW at 350 mA, demonstrating scalability for high-power applications such as night vision and remote sensing. The linear power scaling with current indicates minimal thermal quenching, a critical requirement for continuous-wave operation in industrial monitoring. • • Cr3+ ions in tetrahedral sites serve as an energy transfer bridge, achieving high Cr3+→Ni2+ energy transfer efficiency, as confirmed by X-ray absorption near-edge structure and low-temperature photoluminescence spectra. This mechanistic insight allows rational design of other transition-metal co-doped systems, reducing trial-and-error in phosphor development.