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 crucial for assembling portable NIR light sources. However, developing efficient and thermally stable broadband NIR phosphors remains challenging. Here, a novel Cr³⁺-doped garnet phosphor, Gd₃Sc_1.5In_0.5Ga₃O₁₂:Cr³⁺, is developed by modulating the six-coordinate polyhedral structure. Under 460 nm blue light excitation, it exhibits broadband NIR emission centered at 775 nm with a full width at half maximum (FWHM) exceeding 135 nm, which is attributed to the increased distortion of the B-sites via cation substitution. Specifically, substituting Sc³⁺ with In³⁺ in the designed samples reduces the local site symmetry, overcomes the parity selection rule, and results in greater oscillator strength for electronic transitions, thereby improving optical properties. This leads to an impressive internal quantum efficiency (IQE) of 98.29%, along with excellent thermal stability performance (I_{423 K} = 85.50%), which is conducive to practical applications in NIR light sources. The NIR phosphor-converted light-emitting diode (pc-LED) fabricated with the optimized phosphor and a 460 nm blue LED chip demonstrates an outstanding NIR power conversion efficiency (PCE) of 19.75% at 30 mA and an NIR output power of 276.01 mW at 1200 mA. Potential applications in night vision, non-invasive imaging, and non-destructive testing are explored. These results highlight the enhancement of phosphor performance through cation substitution strategies, achieving a balance between QE and thermal stability. These findings are expected to promote the development of NIR pc-LEDs as high-performance light sources for miniaturized NIR spectrometers.