Mechanism of mechanical quenching and mechanoluminescence in phosphorescent CaZnOS:Cu

This article reports a new phosphorescent material, CaZnOS:Cu, that exhibits two types of mechano-optical conversion: mechanical quenching and mechanoluminescence. An intense mechanical quenching of phosphorescence corresponding to mechanical stimuli can be achieved in CaZnOS:Cu within a short decay time period. Over time, it gradually changes to mechanoluminescence when a mechanical load is applied. We propose that the mechanical quenching and mechanoluminescence arise from the different roles of shallow and deep traps in CaZnOS:Cu. CaZnOS:Cu has promising applications in monitoring mechanical stress in industrial plants, structures, and living bodies. A phosphor has been made that initially exhibits quenching and subsequently excitation of phosphorescence when a mechanical load is applied. Mechanoluminescent materials emit phosphorescence when a compressive load is applied. Recently, Chao-Nan Xu and co-workers at the National Institute of Advanced Science and Technology and Kyushu University in Japan discovered some materials that exhibit the opposite effect, namely quenching of phosphorescence on application of a load. In this study, they found that CaZnOS:Cu shows both effects: intense mechanical quenching of phosphorescence with a short decay time period followed by a gradual change to mechanoluminescence. The researchers propose that the two processes arise from differing roles of shallow and deep traps in the material. They suggest that the material could be used as a stress sensor to monitor stress in industrial plants and living bodies.