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 Na 3 Al 2 Li 3 F 12 :Cr 3+ 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 Cr 3+ 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 Na 3 Al 2 Li 3 F 12 :5%Cr 3+ sample retained ~99% of the PL intensity at room temperature, exhibiting excellent PL thermal stability. A NIR pc-LED was fabricated by combining the Na 3 Al 2 Li 3 F 12 :5%Cr 3+ 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 Na 3 Al 2 Li 3 F 12 :Cr 3+ is a promising candidate for broadband pc-LED in NIR spectroscopy applications.
Lin Xiang,Xianju Zhou,Yongjie Wang,Li Li,Sha Jiang,Guotao Xiang,Chuan Jing,Jingfang Li,Lu Yao
Near infrared (NIR) light emitting phosphors have attracted more and more attention with the development of science and technology . Herein, we report a series of environmentally-friendly low-cost Fe 3+ -activated ZnGa 2 O 4 phosphors which exhibit intense broadband NIR light emitting. According to density functional theory (DFT) calculations, ZnGa 2 O 4 host possesses an indirect wide bandgap. The emission of the Fe 3+ -doped phosphors demonstrates a wide band spanning from 650 to 850 nm, with the maximum at 720 nm and a full width at half maxima (FWHM) of 70 nm, showing a large overlap with the absorption of phytochromes (PR and PFR). The luminescence intensity remains at 71% when the temperature is raised to 423 K. The phosphors are fabricated into light emitting diodes (LEDs) which produces strong NIR emission with CIE color coordinates of (0.65, 0.31). All these results suggest that ZnGa 2 O 4 :Fe 3+ is a promising NIR luminescent material , which is expected to be a candidate for indoor plant culture LEDs.
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