Visual Representation of the Stress Distribution with a Color‐Manipulated Mechanoluminescence of Fluoride for Structural Mechanics

Abstract Mechanoluminescence (ML) materials are capable of converting applied stress into luminescent signals, and offer fascinating potential applications in biomedicine, safety testing, structural diagnosis, and mechanical sensing. Color‐responsive ML sensing, combined with quantitative evaluation of loaded stress, is preferred for visual description and sensing reliability. In this work, Yb²⁺ and Mn²⁺ ions co‐doped MgF₂ with a fascinating ratiometric ML performance are successfully explored. ML color can be manipulated based on the distinct stress‐dependent ML intensity of the activators. Furthermore, a self‐activated orange persistent ML is observed even after the removal of the mechanics stimuli, allowing a delayed stress sensing with the memorized optical signals. Accordingly, a visualized stress sensing with the as‐explored ML composites using the ultraviolet curing 3D printing technique is demonstrated for structural mechanics. Herein, a feasible optical description of the loaded stress distribution in space for objects free from concerns with dimensions and geometrical shapes can be realized, benefiting the study of 3D structural mechanics, especially for complex structures.