Study on preparation, optical properties and mechanism of Zn₂SnO₄:Cr³⁺ with high NIR luminescence intensity

In this work, Zn2SnO4:xCr(3+) with high near-infrared luminescence intensity (broad emission centered at 800 nm and sharp emission at 703 nm) were successfully prepared by high temperature solid state method. Measurements indicated that the samples exhibited obvious photoluminescence as well as persistent luminescence properties. The results of X-ray diffraction indicated that high temperature facilitated the entry of Cr3+ into the Zn2SnO4 crystal lattice and formed replacement doping and promoted the luminescence efficiency of the samples. And, under the condition of 1450 degrees C and 0.002 at% Cr3+ concentration, sample with optimum NIR fluorescence properties was prepared. In the high-temperature sintering process, many defects of Zn2SnO4 were generated, which effectively promoted the formation of vacancies. The energy levels of these lattice defects (trap energy levels) facilitated the sub-stable trapping of electrons and produce afterglow properties. Analysis of luminescence mechanism reveals that the broad emission band centered at 800 nm and the sharp emission peak at 703 nm were derived from the energy level transitions of T-4(2)(F-4)->(4)A(2) and E-2 ->(4)A(2) of Cr3+, respectively. Though, the long afterglow luminescence duration of Zn2SnO4:Cr3+ needs to be further improved compared with gallate-based NIR phosphors, Zn2SnO4:Cr3+ do have a promising application in bio-imaging due to its special NIR emission range.