Long-wavelength broadband near-infrared luminescence of Cr3+ activated tetra-fluoride RbAlF4 and its multifunctional applications

Near-infrared (NIR) light source technology has been integrated into mobile devices with the advantage of portability to provide efficient analysis in many fields. Among them, NIR light in the 850 nm band has attracted much attention due to its unique advantages. In this study, an ultra-broad NIR emission from 700 to 1100 nm with the peak at 839 nm and full width at half-maximum (FWHM) of 151 nm is achieved in a novel tetra-fluoride RbAlF4:Cr 3+ excited by 465 nm blue light, exhibiting a relatively longer emission wavelength and wider FWHM compared with the reported Cr 3+ -doped fluoride phosphors. In-depth research on its crystal structure reveals that Cr 3+ is in a weak crystal field with a distorted octahedral environment, coupled with a strong electron-phonon coupling effect, which prompts the phosphor to exhibit long-wavelength and broad NIR light characteristics. However, these reasons also lead to relatively moderate internal quantum efficiency and thermal stability. Finally, a NIR phosphor-converted light-emitting diode (NIR pc-LED) was fabricated by combining this phosphor with a commercial blue chip, which shows great potential in non-destructive testing, night-vision observation, and biomedical imaging. This work provides new insights into the design of long-wavelength broadband fluoride phosphors.