Multi-site occupation of Cr3+ toward developing broadband near-infrared phosphors

The near-infrared (NIR) light source has a huge potential for foodstuff analysis, biometric identification, physiological monitoring, and night vision technology with real-time and non-destructive advantages. Demand-led growth impels the exploration of novel NIR phosphors with broadband emission. Here we report a new kind of blue-light excitable NIR phosphor Mg7Ga2GeO12: xCr(3+), in which the multi-site occupation of Cr3+ induces broadband NIR emission in the range of 600-1200 nm with a large full width at half maximum (FWHM) of -190 nm and a NIR photoluminescence quantum yield (PLQY) of 12.06% at x = 0.02. The FWHM can be effectively adjusted from 101 to 226 nm via multisite occupancy preference of Cr3+ ions. The PL intensity remains -50% and nearly 100% of the initial level after heated up to 400 K and immersed in hot water (100 degrees C) for 24 h, respectively, demonstrating good thermal stability and robust chemical stability. The broadband emission originated from multi-site PL centers of Cr3+ is discussed in detail by the temperature-dependent PL behaviors and PL decay lifetime. Finally, a broadband emission NIR-LED is fabricated, based on which a proof-of-concept application for night vision is demonstrated. This work not only provides a strategy for the design and developing of novel broadband NIR phosphors, but also indicates the potential for various advanced spectroscopy applications.