A promising route for developing yellow long persistent luminescence and mechanoluminescence in CaGa2O4:Pr3+,Li+

Abstract

In this study, we identified a novel yellow long persistent luminescent phosphor of Pr³⁺,Li⁺-doped CaGa₂O₄ (CGO) and investigated its crystal structure, photoluminescence (PL), long persistent luminescence (LPL), thermoluminescence (TL) and mechanoluminescence (ML). The crystal structure of CGO can be described as [GaO₄] tetrahedrons connected with each other, forming large tunnels at the center, which are filled by Ca²⁺. Defects are likely to exist in such a structure, which are also beneficial to the generation of LPL and ML. The spectrum analysis shows the yellowish PL of CGO:Pr³⁺,Li⁺, which is attributed to the transitions of Pr³⁺. However, the LPL of CGO:Pr³⁺,Li⁺, with a yellow afterglow lasting for nearly 6 hours (above 0.32 mcd m⁻²), originates from Pr³⁺ and the host. According to TL analysis, the traps of CGO:Pr³⁺,Li⁺ mainly come from the intrinsic defects of CGO, and doping with Pr³⁺ could greatly increase the trap concentration. Moreover, co-doping with Li⁺ as the charge compensating agent and cosolvent can not only enhance the trap concentration, but also adjusts the LPL emission. The highly anisotropic crystal structure of CGO is the main cause of the yellow ML. The similarities between the ML and LPL spectra suggest that they have common emission centers. Finally, a feasible mechanism is proposed to illustrate these LPL and ML processes.