The broadband emission of Cr3+-doped CaY2Mg2Ge3O12 and its applications for NIR detectors†

A phosphor-converted light-emitting diode (pc-LED) is a prime light source in smart broadband near-infrared (NIR) spectroscopy. The performance of NIR pc-LEDs crucially depends on the employed NIR luminescent materials. In this study, we synthesized a novel high-efficiency broadband NIR phosphor, CaY₂Mg₂Ge₃O₁₂:Cr³⁺ (CYMG:Cr³⁺). Under 450 nm excitation, CYMG:Cr³⁺ exhibited remarkable broadband NIR emission from 650 to 900 nm with a full width at half maximum (FWHM) of 115 nm. Within the CYMG lattice, the Cr³⁺ ion occupies Ca/Y sites in the dodecahedron Ca/YO₈ and Mg sites in the octahedron MgO₆, giving rise to two distinct Cr³⁺ luminescence centers. Remarkably, the emission at 100 °C remained at 92% of its room temperature intensity and 81% at 150 °C, showcasing its exceptional thermal stability. The internal quantum efficiency (IQE) reached an impressive 81.1%, with an activation energy ΔE of 0.324 eV. Furthermore, we integrated the CYMG:Cr³⁺ phosphor with a commercial 450 nm blue chip to fabricate a micro NIR pc-LED, which exhibited stable NIR emission across different driving currents, with a NIR output power of 49.65 mW@400 mA and a photoelectric conversion efficiency of 10.52% at 20 mA. All findings highlight CYMG:Cr³⁺ as a stable and efficient broadband luminescent material for high-performance NIR LEDs.