An efficient garnet-structured Na3Al2Li3F12:Cr3+ phosphor with excellent photoluminescence thermal stability for near-infrared LEDs

The emerging applications of near-infrared (NIR) spectroscopy technology in medicine and food security call for compact and efficient NIR light source such as NIR phosphor converted LEDs (pc-LED). Currently, most of the NIR phosphors suffer from low photoluminescence (PL) quantum yield and poor thermal or chemical stability. Herein, a fluoride garnet NIR Na3Al2Li3F12:Cr3+ phosphor was successfully synthesized via coprecipitation method. It can be excited efficiently by blue or red light and shows a broad emission band covering 650–1000 nm (bandwidth of ~110 nm) with a PL quantum yield of 78%. The fine electronic structure of Cr3+ ions in the host was revealed by the measurement of temperature-dependent (8–300 K) excitation and emission spectra analysis. Particularly, at 423 K, the Na3Al2Li3F12:5%Cr3+ sample retained ~99% of the PL intensity at room temperature, exhibiting excellent PL thermal stability. A NIR pc-LED was fabricated by combining the Na3Al2Li3F12:5%Cr3+ phosphor with a commercial blue LED chip, and radiant flux of 14.3 mW in NIR region was obtained at 60 mA drive current. Furthermore, the penetration of NIR light generated by this pc-LED in chicken breast was reached. The results suggested that Na3Al2Li3F12:Cr3+ is a promising candidate for broadband pc-LED in NIR spectroscopy applications.