Inducing B-site distortion in Gd3Sc1.5In0.5Ga3O12 garnet to accommodate Cr3+ ions: achieving high quantum efficiency and thermally stable broadband NIR phosphors for NIR spectroscopy applications
Broadband near-infrared (NIR) phosphors are essential for portable NIR light sources, yet achieving high quantum efficiency (QE) and thermal stability simultaneously remains a persistent challenge. This study reports a Cr3+-doped garnet phosphor, Gd3Sc1.5In0.5Ga3O12:Cr3+, engineered via B-site cation substitution to induce local structural distortion. The substitution of Sc3+ by In3+ reduces the symmetry of the six-coordinate polyhedra, lifting the parity selection rule and enhancing the oscillator strength of Cr3+ 3d-3d transitions. Under 460 nm blue excitation, the phosphor exhibits broadband NIR emission centered at 775 nm with a full width at half maximum (FWHM) exceeding 135 nm. The optimized material achieves an internal quantum efficiency (IQE) of 98.29% and maintains 85.50% of its room-temperature emission intensity at 423 K. A prototype NIR phosphor-converted LED (pc-LED) fabricated with this phosphor and a 460 nm blue chip delivers a power conversion efficiency (PCE) of 19.75% at 30 mA and an NIR output power of 276.01 mW at 1200 mA. These results demonstrate that cation substitution strategies can effectively balance QE and thermal stability, offering a viable route for high-performance NIR pc-LEDs in miniaturized spectrometers, night vision, and non-invasive imaging.