Robust Solar‐Blind Ultraviolet Mechanoluminescence in Flexible Elastomers Without Pre‐Irradiation

Flexible mechanoluminescence (ML) composite elastomers have emerged as promising materials for wearable devices, sensing, and monitoring applications. However, most reported systems emit predominantly in the visible or near-infrared region, which can only be effectively detected in darkness. Solar-blind ultraviolet (UV) ML systems that can be monitored under all-weather conditions, in contrast, remain scarce and typically rely on pre-irradiated phosphors. Herein, a robust solar-blind ultraviolet-C (UVC) ML composite elastomer composed of polydimethylsiloxane (PDMS) and Sr₃(PO₄)₂:Pr³⁺ (SPO:Pr) phosphors is developed. This composite elastomer exhibits self-powered and self-recovered UVC emission centered at 264 nm in response to various mechanical stimuli, such as stretching, rubbing, and impacting. Notably, it demonstrates remarkable repeatability and cyclic stability, maintaining detectable UVC emission over 10,000 continuous stretching cycles (the UVC power intensity during the first cycle can reach 12.1 mW·m^-2), accompanied by rapid self-recovery behavior. Comprehensive experimental analyses reveal that interfacial triboelectrification, originating from electron transfer from the SPO:Pr phosphors to the PDMS matrix, dominates the underlying UVC ML mechanism. This new series of pre-irradiation-free and self-recoverable UVC ML elastomers holds great potential for practical applications under all-weather conditions, such as structural failure monitoring, covert optical tagging and tracking, and collision detection.