Thermodynamic Stabilization and Cr ³⁺ Luminescence Tuning in Gd ₃ Al ₅ O ₁₂ Garnet Phosphor via Multi‐Cation Incorporation

To explore broadband near‐infrared (NIR) emission phosphor based on the thermodynamic metastable Gd 3 Al 5 O 12 garnet, a new strategy of Ca 2+ ‐Sn 4+ pairs substituting for Gd 3+ ‐Al 3+ was utilized to stabilize the lattice, followed by using Ga 3+ doping to tune the crystal structure, Cr 3+ local coordination environment, and luminescence. Then the novel Gd 1.02 Ca 1.98 Al 3− y Ga y Sn 1.98 O 12 :0.02Cr 3+ (GCAGSO:Cr) phosphors were successfully devised and fabricated, and systematic research revealed that increased Ga 3+ incorporation induced an enhanced degree of the [(Sn,Ga,Cr)O 6 ] octahedron distortion, weakened the magnitude of the crystal field Cr 3+ experienced, and red‐shifted/broadened the emission band. The optimal phosphor exhibits efficient broadband NIR emission and outstanding thermal stability ( I 423K = 84.3%, S = 3.52, Δ E a = 0.31 eV), with a maximum center at ∼782 nm, a full‐width at half‐maximum of ∼138 nm, and internal/external quantum efficiencies of ∼80.3%/24.2%. The constructed pc‐NIR‐LED adopting this optimal phosphor manifests desirable luminous performance (output power ∼19.05 mW, efficiency ∼8.24%), demonstrating promise for practical applications in non‐invasive biological imaging, non‐destructive inspection, and night vision.