Heterovalent Co‐Occupation Strategy Unlocks Self‐Activating Multicolor Mechanoluminescence for Visualizing Muscle Activation and Advanced Anti‐Counterfeiting

ABSTRACT Self‐activating mechanoluminescent (ML) materials are highly promising for wearable biomechanical monitoring, while their application is severely restricted by monochromatic emission and limited repeatability. Here, we break this limitation via a “heterovalent co‐occupation” cationic design strategy, leading to a new family of SrLaGa 3 O 7 :X 3+ (X = Tb, Pr, Sm, Eu, Dy, Bi) phosphors. When mixed with polydimethylsiloxane, the fabricated flexible ML elastomers exhibit self‐activating, repeatable, and vivid multicolor emission under mechanical stimuli. Cathodoluminescence and triboelectric potential measurements clarify that the ML emission originates from a triboelectric field at the particle–polymer interface, requiring no pre‐irradiation. Benefiting from their unique multicolor and repeatable ML, these composites enable advanced high‐security anti‐counterfeiting and handwritten force mapping. Furthermore, we develop a novel application for visualizing muscle activation regions during fitness training, providing real‐time feedback. This work not only provides a versatile design strategy for novel multicolor self‐activating ML materials but also paves the way for a new generation of visualized human motion monitoring.