Controlling Cr3+/Cr4+ concentration in single-phase host toward tailored super-broad near-infrared luminescence for multifunctional applications

Full control on the valence of the active ions in solids to improve properties is the central topic of chemistry and materials. Cr3+ and Cr4+ ions generally emit wavelength-different near-infrared (NIR) light. Here, we have developed a chromium valence-controllable single-phase phosphor, Mg2GeO4:Cr3+,Cr4+ to achieve super-broad NIR luminescence. High Li + content charge compensators can stabilize Cr3+, whereas high-temperature sintering tends to facilitate the formation of Cr4+. Through fine adjusting the synthesis conditions, pure Cr3+ or Cr4+ luminescence can be obtained with peak emission locating at 935 nm and 1190 nm, respectively. Super broad band dual emission spanning from 650 nm to 1600 nm is realized via fully controlling the concentration ratio of Cr3+ to Cr4+ in a single host. By measuring the transmission spectra of several foodstuff illuminated by our phosphors, non-destructive analysis in food safety areas can be realized. This study provides a new strategy for exploiting super broad band NIR luminescent materials.