Modeling Polyhedron Distortion for Mechanoluminescence in Mixed-Anion Compounds RE2O2S:Ln3+

Mechanoluminescent (ML) materials with the characteristics of photon emission under mechanical stimulation show broad application prospects in building structural health diagnosis, biomechanical engineering, and wearable devices. However, existing ML materials cannot fully meet the requirements of different stress sensing applications due to the limited understanding of the structure and mechano-to-photon conversion mechanism of ML materials. Herein, we report novel ML materials with excellent self-recoverable ML performance in the family of mixed-anion compounds RE2O2S:Ln(3+) (RE = Y, Lu, La, Gd). The ML intensity is linearly related to the applied force, and the ML wavelength is tunable over a broad range of 514-1550 nm. More importantly, we construct a polyhedron distortion model that describes the local symmetry breaking. This model well explains the origin of ML and piezoelectricity in the compounds with centrosymmetric crystal structures. The findings may deepen the understanding of the microstructure and the mechano-to-photon conversion mechanism in ML materials and are expected to provide important guidance for the development of high-performance ML materials.