Synergistic Optimization Between Chromium Local Coordination States Toward Self-Powered High-Repeatability...

Self-powered mechanoluminescence (S-ML) elastomer with near-infrared (NIR) emission exhibits great potential for the next generation of bio-imaging, bio-sensing, and human-machine interaction fields. However, due to the lack of understanding of the mechanical-photon conversion mechanism, the emission efficiency and cycling stability of ML materials reported so far are still unable to meet the application needs. Herein, high-repeatability (>10000 times) and tunable near-infrared (650-1000 nm) mechanoluminescent materials are reported by optimizing Cr³⁺ local coordination states in a simple centrosymmetric MgO host. The constructed electron transfer model among multiple Cr³⁺ ion states (isolated Cr³⁺, Cr³⁺ pair, and Cr³⁺ cluster) reveals the structure-activity relationship between local piezoelectricity and photoelectric output. Theoretical calculations and experimental results reveal that the heterovalent substitution of Cr³⁺ ions promotes the [MgO₆] distortion to activate the nearest neighboring defect to form suitable intermediate gap states, facilitating stress-driven electron tunneling to Cr³⁺ states. Proof-of-concept multi-layered bright field sensing and imaging is developed with all-round interactive NIR tactile perception. This work not only provides a high-repeatability NIR ML phosphor but also establishes the integrated thinking mode for material-performance-device rational design.