Interfacial Triboelectricity Lights Up Phosphor‐Polymer Elastic Composites: Unraveling the Mechanism of Mechanoluminescence in Zinc Sulfide Microparticle‐Embedded Polydimethylsiloxane Films

Composites comprising copper‐doped zinc sulfide phosphor microparticles embedded in polydimethylsiloxane (ZnS:Cu–PDMS) have received significant attention over the past decade because of their bright and durable mechanoluminescence (ML); however, the underlying mechanism of this unique ML remains unclear. This study reports empirical and theoretical findings that confirm this ML is an electroluminescence (EL) of the ZnS:Cu phosphor induced by the triboelectricity generated at the ZnS:Cu microparticle–PDMS matrix interface. ZnS:Cu microparticles that exhibit bright ML are coated with alumina, an oxide with strong positive triboelectric properties; the contact separation between this oxide coating and PDMS, a polymer with strong negative triboelectric properties, produces sufficient interfacial triboelectricity to induce EL in ZnS:Cu microparticles. The ML of ZnS:Cu–PDMS composites varies on changing the coating material, exhibiting an intensity that is proportional to the amount of interfacial triboelectricity generated in the system. Finally, based on these findings, a mechanism that explains the ML of phosphor–polymer elastic composites (interfacial triboelectric field‐driven alternating‐current EL model) is proposed in this study. It is believed that understanding this mechanism will enable the development of new materials (beyond ZnS:Cu–PDMS systems) with bright and durable ML. This study demonstrates that the mechanoluminescence observed in ZnS:Cu‐PDMS composites is attributed to the electroluminescence of ZnS:Cu phosphors induced by the triboelectricity generated at the interface between ZnS:Cu and the PDMS matrix. The intensity of ML is influenced by variations in the interfacial composition, which directly correlates with the interfacial triboelectricity. Based on the experimental findings, a theoretical model is proposed to elucidate the mechanism underlying ML generation in ZnS:Cu‐PDMS composites.