Tunable NIR long persistent luminescence and discovery of trap-distribution-dependent excitation enhancement in transition metal doped weak-crystal-field CaZnGe2O6

A long persistent phosphor (LPP) CaZnGe2O6: Cr3+ has been rationally designed and successfully fabricated. The weak crystal field surrounding Cr3+ activator enables an afterglow emission band 700-1200 nm almost covering the biological transparency window. In this work, a feasible route of Mn2+ codoping is suggested to precisely control the spectral shape, which further meets the demand of wide range and steady response to different photo-detectors in the biological transparency window. An interestingly synchronous improvement of persistent duration of Cr3+ and Mn2+ emission center is discovered in this process. Meanwhile, this codoping technique also achieves the enhancement of afterglow-excitation intensity. The design approach employed here inherently involves the ingenious engineering for combining the isolated traps in Cr3+, Mn2+ singly doped LPP, and for forming a continuous-distribution trap in Cr3+, Mn2+ co-doped LPP according to the thermoluminescent measurement. The highlighted redeployment of trap distribution will opens a vista of potential avenues for LPP design, afterglow mechanism analysis and functionalized application of bio imaging.