Self-Recovering Multicolor Calcium Phosphate Mechanoluminescent Materials for Wearable Skin and Biomedical Applications

Mechanoluminescent (ML) materials are promising for applications in structural health monitoring, biomedicine, stress sensing, and stress distribution visualization due to their ability to emit light without external circuits. However, current ML materials face challenges, including limited luminescent colors, high raw material costs, toxicity, and lack of emissions in the invisible light spectrum. To overcome these challenges, Ca₂P₂O₇ (CPO) is selected as the matrix material due to its excellent piezoelectric properties, low cost, and biocompatibility. CPO is doped with various luminescent ions (X, X = Ce³⁺, Eu^2+/3+, Tb³⁺, Dy³⁺, Mn²⁺, Sm³⁺) to achieve the emission bands of CPO:X across a wide range of wavelengths including UV, blue, green, yellow and red. Unlike traditional trap-controlled ML materials, CPO:X does not require UV pre-irradiation and exhibits remarkable self-recovery properties. First-principles density functional theory (DFT) calculations confirmed that CPO is an ideal matrix for self-recovering ML materials. Based on these properties, several practical devices are designed, including a fencing competition scorekeeper, a wearable flexible skin, and a protective dental crown layer. These innovations offer new directions for the development and application of ML materials.