Bright yellow pigment and broadband NIR-I phosphor based on octahedral coordinated mix-valence Cr in Ca2LiScB4O10

The novel yellow color compounds Ca2LiSc1-xB4O10: xCr with NIR emission were successfully synthesized by the solid state method. All samples are of pure phases through X-ray diffraction results. The oxidation state of Cr dopant in this borate is confirmed to be mix-valence (+3 and + 6) using XPS analysis. Based on the analysis of Cr oxidation state and UV–Visible spectrum, the Cr–O charge transfer from Cr6+ octahedral sites in the visible light range is the reason for the yellow color. Meanwhile, a near infrared (NIR) broadband emission at 800 nm with FWHM of 141 nm is from Cr3+ in octahedron, which could be effectively excited by 495 and 630 nm. The yellow chromophore and NIR lumophore are successfully combined in Ca2LiScB4O10: Cr using economical raw materials through simple method, and may be applied in the field of yellow pigment and NIR phosphor.