Designing a novel red to near-infrared persistent phosphor CaMgGeO:Mn,Sm based on a vacuum referred binding energy diagram.

In this work, we designed and successfully synthesized a novel germanate-based persistent luminescence (PersL) phosphor host, CaMgGeO, via a solid-state reaction. We constructed an empirical energy level scheme of the CaMgGeO:Ln/Ln phosphors according to the Dorenbos model. Then, we successfully theoretically predicted the choice of the optimal codopant of CaMgGeO:Mn phosphors using this empirical energy level scheme. As a result, after co-doping with Sm, the PersL intensity is increased 16 times and the time duration is effectively improved 52 times due to the high concentration of new traps. CaMgGeO:Mn,Sm shows red to near-infrared long persistent emission located at 675 nm, which can be sustained for about 60 minutes above the recognizable intensity level (≥0.32 mcd m), and the persistence duration of samples was three times that of the red commercial phosphor YOS:Eu. The experimental results coincide well with the theoretical predictions. These results demonstrate that the strategy concepts of this work are feasible for the design of persistent luminescence materials. Moreover, a possible afterglow mechanism is studied and discussed with the assistance of thermoluminescence (TL) curves.