Cr3+-Activated Mg4GaSbO8 Orthorhombic Spinel-Derived Phosphors with Multisite Occupation for Tunable Broadband Near-Infrared Emission

High-performance broadband near-infrared (NIR) phosphors are essential for the development of state-of-the-art NIR phosphor-converted light-emitting diodes (pc-LEDs). Herein, we report a novel Cr3+-doped Mg4GaSbO8 (MGSO) luminescent material based on an orthorhombic spinel-derived superstructure featuring multiple crystallographically distinct octahedral sites. By precisely modulating Cr3+ concentration, NIR emission with a remarkable tunability in full width at half-maximum from 100 to 308 nm is realized. Comprehensive spectroscopic analyses reveal three inequivalent Cr3+ emission centers (CrI, CrII, and CrIII) arising from selective substitution at Mg1, Mg2, and Mg3 octahedral sites with progressively weakened crystal fields. Increasing dopant concentration drives sequential site occupation and energy transfer among Cr3+ centers, leading to pronounced spectral redshift and ultrabroadband emission. The optimized MGSO:0.07Cr3+ shows a high quantum yield of 80.4% and solid thermal stability with 85.6% emission intensity retention at 373 K. At high doping levels (x = 0.20), the phosphor exhibits reduced thermal robustness but exceptional spectral broadening. Finally, MGSO:Cr3+ was integrated into NIR pc-LED prototypes, underscoring their potential applicability in nondestructive inspection and NIR spectroscopy.