Nonequivalent Substitution and Charge-Induced Emitter-Migration Design of Tuning Spectral and Duration Properties of NaCa2GeO4F:Mn2+ Persistent Luminescent Phosphor

We combine nonequivalent substitution and charge-induced emitter-migration approaches and design an efficient method to optionally tune the spectral and duration properties of NaCa2GeO4F:Mn2+ phosphor. A series of representative codopants have been investigated in detail and classified into two categories: R-A (R-A = Li+, Al3+, N3-, Ga3+, B3+) and R-B (R-B = Mg2+, F-, Bi3+, Zn2+, Cd2+, Sc3+, Tm3+). Results reveal that the nonequivalent substitution of RA codopants would induce foreign negative defects and stabilize Mn2+ emitters at octahedral Na/Ca sites for red emission. In constrast, the R-B codopants would generate foreign positive defects and make Mn2+ emitters migrate to tetrahedral Ge4+ sites for green yellow emission. At the same time, the R-A codopants are in favor of the generation of intrinsic positive traps with shallow trap depth and thus efficiently improve the duration properties of phosphors. On the basis of the experimental results, a possible nonequivalent substitution and charge-induced emitter-migration model has been proposed, and we can optionally tune the spectral (568 <-> 627 nm) and the duration (minutes to more than 6 h) properties according to this model.