Structure and Luminescence Regulation in Y ₃ Al ₅ O ₁₂ :Cr ³⁺ via Cation Substitution to Achieve Broadband Near-Infrared Emitting Garnet Phosphor

To modulate the structure and optical properties of Cr³⁺-activated Y₃Al₅O₁₂ garnet with typical narrowband near-infrared (NIR) emitting, cation substitution was implemented to establish novel Y3-xCaxAl5-xSnxO₁₂:yCr³⁺ broadband NIR phosphors in this work. Density functional theory calculations, Rietveld refinement, X-ray photoelectron spectroscopy, and UV-vis-NIR/photoluminescence spectroscopy analysis clearly elucidated that the equimolar Ca²⁺ and Sn⁴⁺ doping led to the expansion of the lattice and the enhanced distortion degree of the [(Al,Sn,Cr)O₆] octahedron. They thus resulted in a reduction in the crystal-field magnitude and in a massive redshift and spectral broadening of the emission band. The optimal x = 1.5/y = 0.06 phosphor manifested wide-band NIR emission with a center at ∼764 nm and a full width at half-maximum of ∼135 nm, a high luminous efficiency (internal quantum efficiency = 75.6% and external quantum efficiency = 25.1%), and favorable thermal stability (74.5% at 423 K). The manufactured pc-NIR-LED device using this optimal phosphor exhibited satisfactory NIR output power (∼21.1 mW) and efficiency (8.53%), signifying that this garnet phosphor has potential for application in the construction of pc-NIR-LEDs for night vision, noninvasive medical diagnosis, and nondestructive detection.