Unlocking Broadband Near-Infrared Luminescence from Cr³⁺-Activated NaGd₂Ga₃Ge₂O₁₂ Garnet Induced by Intrinsic Cation Disorder.

Integrating near-infrared (NIR) activators into host lattices with intrinsic cation disorder yields broadband luminescence for phosphor-converted LEDs, yet the microscopic mechanism for the structure-property relationship remains elusive. Here we report a novel Cr³⁺-activated NIR-emitting phosphor, NaGd₂Ga₃Ge₂O₁₂:Cr³⁺, featuring intrinsic Na/Gd and Ga/Ge site-occupation disorder in the second coordination shell of Cr³⁺. The multiple distinct crystal-field sites created by the intrinsic disorder enables Cr³⁺ to emit inhomogeneously from 600 to 1300 nm with a maximum (λmax) at 820 nm. Co-doping Sc³⁺ widens the emission band to a full width at half-maximum of 183 nm while retaining an internal quantum efficiency of 85%, an external quantum efficiency of 35%, and a thermal stability of 71% at 423 K. These figures are on par with previously reported best-performing Cr³⁺-activated intrinsic disordered garnet phosphors with λmax > 800 nm. Density functional theory calculations are conducted to elucidate the underlying mechanism in correlation with random second neighbors and Sc³⁺ influence on the band gap. The fabricated NIR pc-LED demonstrates application potential in night vision, nondestructive examination, and information encryption. This work underscores intrinsic structural disorder as a design route to high-performance broadband NIR phosphors.