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 (Dq/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.

Interstitial Li+ Occupancy Enabling Radiative/Nonradiative Transition Control toward Highly Efficient Cr3+-Based Near-Infrared Luminescence.

Highly efficient and stable broadband near-infrared (NIR) emission phosphors are crucial for the construction of next-generation smart lighting sources; however, the discovery of target phosphors remains a great challenge. Benefiting from the interstitial Li+ occupancy-induced relatively large distorted octahedral environment for Cr3+ and suppressed nonradiative relaxation of the emission centers, an NIR emission fluoride phosphor Na3GaF6:Cr3+,Li+ peaking at 758 nm with a high internal quantum efficiency of 95.8% and an external quantum efficiency of 38.3% is demonstrated. Moreover, it exhibits a good thermal stability (84.9%@150 °C of the integrated emission intensity at 25 °C) and excellent moisture resistance as well. A high-power light-emitting diode (LED) with a record watt-level NIR output (974.12 mW) and a photoelectric conversion efficiency of 20.9% is demonstrated by combining Na3GaF6:Cr3+,Li+ and a blue InGaN chip, and a special information encryption/decryption technology suitable for rapid and long-distance identification of machines is further presented based on this device. This study not only advances the development of efficient NIR emission phosphors for broadband NIR LEDs but also for NIR-related emerging applications and devices.