Dual-Functional Alumina Additive Enabling Efficient, Volumetric Mechanoluminescence for Nighttime Safety Footwear

Visualizing mechanical force distribution through mechanoluminescent foams allows real-time optical monitoring of human motion for energy, sensing, and safety applications. However, conventional polymer-based mechanoluminescent composites often suffer from inefficient stress transmission in thick structures due to their high elasticity, resulting in surface-confined emission and weak luminescence in the global regions. In this study, Al₂O₃ is introduced as a simple additive that performs dual functional roles in both structural and electrical aspects. During fabrication, surface-adsorbed species on Al₂O₃, such as oxygen and moisture, induce spontaneous bubble formation, generating a sponge-like porous architecture that enhances force dispersion and consequently improves mechanoluminescent performance in the global region of the foam. Moreover, the intrinsically strong positive triboelectricity of Al₂O₃ strengthened the interfacial triboelectric field, leading to highly bright emission even with a low loading ratio of ML particles. When applied to shoe soles, the foam enables not only full-area signal monitoring but also spatially resolved detection of dynamic loading during human motion. This study reveals the dual structural and triboelectric enhancements induced by a simple additive and highlights its potential for realizing practical self-luminous platforms in smart footwear, healthcare monitoring, and wearable stress sensing.