Broadband near-infrared light source derived from Cr 3+ -doped phosphors and a blue LED chip

NIR-emitting YAl3(BO3)4:Cr3+/Yb3+ (YAB:Cr/Yb) and NaScSi2O6:Cr3+ (BSSO:Cr) phosphors were demonstrated as luminescent converters for broadband NIR phosphor-converted LEDs (pc-LEDs). YAB:Cr/Yb phosphors show emissions in 670–800 nm (Cr3+ emission) and 950–1050 nm (Yb3+ emission) upon excitation at 450 nm. In the BSSO host, Cr3+ ions occupy Sc3+ sites with relatively weak crystal field, and thus a broadband Cr3+ emission at longer wavelengths of 750–950 nm is found for BSSO:Cr phosphors. Moreover, temperature-dependent spectral studies indicate that both YAB:Cr/Yb and BSSO:Cr phosphors exhibit good thermal stability, and more than 80% of the initial emission intensities can be sustained at 150°C. A NIR pc-LED prototype was fabricated by integrating these two phosphors with a blue LED chip (∼450 nm), which generated a broadband emission in the NIR spectral range from 780 to 1050 nm. A NIR light output power of ∼26 mW was achieved at the injection current of 100 mA, with the corresponding energy conversion efficiency of ∼8.6%.