Correlation between persistent luminescence and mechano-luminescence of Sm3+-doped YPO4

Abstract

Persistent luminescence (PersL) and mechanoluminescence (ML) are two interesting optical phenomena, which are initiated by trapped charge carriers in some materials upon applying heat or force stimulations. Therefore, it is meaningful to jointly investigate PersL and ML in a single material to better understand the correlation between them. Herein, we focused on Sm³⁺-doped YPO₄ because it can emit both PersL and ML. On the one hand, we demonstrated that after being charged by X-ray, YPO₄:Sm³⁺ emitted orange PersL for over one hundred minutes, which can be attributed to the ⁴G_5/2 → ⁶H_7/2 transition of Sm³⁺. During the PersL stage, Sm³⁺ ions consistently served as luminescent centers. Using thermoluminescence measurements, we confirmed a continuous distribution of traps in YPO₄:Sm³⁺, with trap depths ranging from 0.59 to 0.81 eV. On the other hand, during the PersL process, we observed a significant enhancement in YPO₄:Sm³⁺ upon receiving an external force stimulation. It suggested that in addition to heat, external force stimulation enabled the release of the same trapped charge carriers in YPO₄:Sm³⁺, resulting in ML. Additionally, we confirmed that the ML of YPO₄:Sm³⁺ belonged to the trap-controlled type, with both piezoelectric and triboelectric effects playing pivotal roles in the force-activated luminescence process. Our work offers insights into the coupling between PersL and ML, laying the foundation for the rational design of future multi-stimuli responsive luminescent materials.