Visible droplet luminescence in daylight

Droplet luminescence (DL), which is based on the coupling of contact electrification and electroluminescence, has great potential in various fields owing to its unique motion-driven optical response. However, the current DL method is limited by its weak intensity, complex structure, and laborious techniques. In this study, intense DL, visible even in daylight, was realized using a facile method. An exact multi-physics simulation confirmed that DL could be directly excited by the interfacial electric field in liquid-solid contact without any pretreatment. A relevant strategy of semi-embedding luminescent particles in ultra-thin polymer film was proposed to ensure sufficient liquid-solid contact to transfer the interfacial charge and maximize the direct excitation of luminescent particles by the interfacial electric field. This bright DL demonstrates considerable potential for practical applications in sensors, display, and information storage. More importantly, this DL throws a light onto the liquid-solid interface for visualizing the dynamic process of charge transfer throughout the liquid-solid contact, which may provide insights for the exploration of interfacial charge transfer.