Achieving high performance ultra-broadband near-infrared emission through a multi-site occupancy and energy transfer strategy for NIR LED applications†

Broadband near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are considered to be at the forefront of the development of next-generation NIR light sources. However, the performance of NIR pc-LEDs is severely limited due to the narrow band emission, low quantum efficiency, and thermal quenching of NIR-emitting materials. Herein, an efficient and thermally stable broadband NIR LaMgGa₁₁O₁₉:Cr³⁺,Yb³⁺ (LMG:Cr³⁺,Yb³⁺) phosphor has been successfully designed by [Cr³⁺–Yb³⁺] co-doping. The broadband emission phenomenon of LaMgGa₁₁O₁₉:Cr³⁺ was confirmed to be due to selective lattice occupancy of Cr³⁺ ions based on the analysis of crystal structures, crystal field calculations, and fluorescence lifetimes. The NIR emission spectra in the range of 1000–1200 nm were enriched by using the highly efficient energy transfer of Cr³⁺ → Yb³⁺ ions and the energy transfer mechanism is discussed in detail. The prepared LMG:Cr³⁺,Yb³⁺ phosphors exhibit highly efficient ultra-broadband NIR emission from 650 to 1200 nm under 440 nm excitation with high internal and external quantum efficiencies of 94.2%/40.5% and excellent luminescence thermal stability of 89.3%@373 K. A NIR pc-LED prototype was fabricated by combining the optimized phosphor with a commercial 440 nm blue LED chip, providing 84.5 mW NIR output power at a 350 mA driving current. Finally, the potential applications of the phosphor in night vision lighting and non-destructive testing were demonstrated. The results show that this work is expected to provide a new strategy for efficient ultra-broadband NIR phosphor design.