Broadband short-wave near-infrared-emitting phosphor MgNb₂O₆:Cr³⁺ for pc-LED applications

Broadband short-wave near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) have been attracting keen interest for miniature NIR spectroscopy, while still lacking sufficient novel broadband NIR-emitting phosphors. Herein, we report a novel MgNb₂O₆:Cr³⁺ polycrystalline phosphor with a broad NIR emission band centered at 970 nm and a large full-width at half-maximum of approximately 155 nm under excitation of bluish-green light at around 515 nm. The optimized phosphor MgNb₂O₆:1%Cr³⁺ features a high internal quantum efficiency (IQE) of ∼85.5% and a moderate external QE of 25.2%. The fluorescence properties determined by two distorted hexa-coordination octahedral sites (i.e. [MgO₆] and [NbO₆]), low crystal field strength (D_q/B ∼ 1.65), and Cr³⁺-doping concentration were systematically investigated for comprehensive understanding of photophysical mechanisms. Besides, this broadband NIR phosphor MgNb₂O₆:Cr³⁺ exhibits a moderate thermal quenching of 21.4%@373 K for pc-LED application. An NIR pc-LED self-built by combining the optimal phosphor with a commercial cyan of ∼515 nm exhibits an NIR output power increase from 3.19 to 11.38 mW as the drive current is varied from 40 to 220 mA. With the help of this prototype pc-LED device, multiple applications were successfully performed to clearly recognize blood vessel distributions in the human finger, penetrate a plastic cap, and distinguish multi-color text. Undoubtedly, further development of such broadband short-wave NIR-emitting phosphors will make novel pc-LED devices for significant applications in biomedical imaging, nondestructive safety detection, intelligent identification, etc.