Color-resolved mechanoluminescence of Eu and Mn co-doped SrMg₂(PO₄)₂

Mechanoluminescence (ML) materials can convert mechanical stimuli into visible signals for real-time visualization of stress sensing. Since stress sensing solely based on ML absolute strength is susceptible to the external environment, ratiometric ML detection approach is expected to provide stress description with improved accuracy and stability. In this study, a stress-dependent ratiometric ML is achieved using the Eu2+ and Mn2+ co-doped SrMg2(PO4)2 (SMP) phosphors, enabling color-resolved visualization of uploaded stress stimulus. Moreover, the linear relationship between the ML intensity ratio (MLIR) and the applied stress leads to an obvious variation in ML color upon different applied stress. Herein, the as-explored ML composites films as an artificial skin could provide a visualization and quantification tool for monitoring human knee motion with great accuracy and precision.