Design and control luminescence of Li2ZnGe3O8:Cr3+ in NIR І region by cationic regulation

Li2ZnGe3O8:Cr3+ deep-red phosphor is synthesized, and the excitation spectrum ranges from 250 nm to 640 nm, and the emission peak locates at 713nm. In order to obtain NIR light, Mg2+/Ca2+/Sr2+/Ba2+ ions were introduced into Li2ZnGeO8:Cr3+. The emission spectra firstly show a blue shift and then present an obvious red shift by tuning the Zn/Mg ratio. A common effect between the crystal field splitting and the nephelauxetic effect makes it possible to blue shift, and the red shift is ascribed to the reduced site symmetry around some Cr3+ ions caused by the disorder. In addition, the emission spectra have a red shift when Zn2+ is substituted by Ca2+, Sr2+ or Ba2+, which is also a common effect between the crystal field splitting and the nephelauxetic effect. As a results, the luminescence materials realize the regulation from deep red to near-infrared light by increasing the doping ionic (Ca2+, Sr2+, and Ba2+) radii.