Delayed stress memory by CaAl₂O₄:Eu²⁺ mechanoluminescent phosphor with defect engineering regulation

Real-time stress sensing based on mechanoluminescence materials has been widely studied for structural health monitoring of bridges, buildings, high-pressure vessels, and other infrastructure surfaces. However, this approach is difficult to detect the stress information of closed mechanical structures. Here, we propose a delayed stress memory strategy to record the stress information of closed mechanical structure by the flexible film composed with CaAl₂O₄:Eu²⁺,Sm³⁺ phosphor. After the force is applied, the optical information on the film can be read out by the near-infrared laser after a period of time without real-time monitoring, and the stress distribution information of bearings and gears in the engine can be obtained. Furthermore, the regulation of trap depth from 0.662 to 1.042 eV allows the captured carriers to remain in the traps for a long time without being released as long persistent luminescence, which is beneficial to the delayed stress memory. Therefore, this work promotes the application prospect of mechanoluminescence materials in stress sensing, and provides a new idea to record the stress information of closed mechanical structures.