Interface-engineered calcium phosphate-hydroxyapatite heterostructure with enhanced full-spectrum mechanoluminescence for bridge stress distribution mapping

Mechanoluminescent (ML) materials, with their self-powered and real-time response characteristics, have demonstrated significant potential in structural health monitoring. However, limitations such as narrow spectral width and insufficient quantitative analysis capability still restrict their practical applications. This work presents an Eu-doped Ca 3 (PO 4 ) 2 /Ca 5 (PO 4 ) 3 OH (CPO/CPOH) heterostructured ML material. By synergistically optimizing interfacial electron behavior and phase composition, this heterostructure design increases ML intensity by 230 % compared to single-phase materials. Notably, an interface-induced Eu 3 + →Eu 2+ self-reduction phenomenon is first observed . Introducing a reducing atmosphere , ML intensity is further amplified by 10.7 times, and full-spectrum ML emission with a full width at half maximum (FWHM) of 170 nm is successfully realized. Density functional theory (DFT) calculations confirm that the oxygen-bridge-connected interface structure exhibits thermodynamic stability, and directional electron transfer from CPO to CPOH reduces the system band gap (2.73 eV), providing an efficient pathway for carrier migration. Combined with thermoluminescence analysis, cycling stability, and interfacial electric field correlation, the ML mechanism is clarified as an interfacial electric field-driven carrier detrapping process. Furthermore, by integrating digital image correlation (DIC) technology with Lagrange transformation, this material successfully visualizes and enables quasi-quantitative analysis of stress concentration regions (0.05 - 1.16 MPa) in bridge structures, validating compressive performance differences among T-beam bridges, cylindrical bridges, and arch bridges. This study not only provides a novel heterostructure ML system and regulating spectral properties but also establishes a reliable visual quasi - quantitative analysis platform for real-time health monitoring of large-scale structures.