Effect of local structural symmetry on mechanoluminescencent materials

Mechanoluminescent materials exhibit light emission in response to mechanical stimuli.Its intensity is expected to be correlated with the local symmetry around the luminescent center.This study aimed to quantitatively investigate the correlation between the D index, representing the distortion of the oxide ion coordination polyhedron around the luminescence center, and mechanoluminescence (ML) intensity, focusing on four representative ML materials.The materials studied, including SrAlO:Eu (SAO), SrSnO:Sm (SSS), (Li, Na)NbO (LNNO), and SrSnO:Nd (SSN), exhibited visible and near-infrared ML.For these materials, the average D index, considering the occupancy and multiplicity of luminescent center, was determined from the Rietveld analysis of X-ray powder diffraction patterns, and a quantitative comparison was made with ML intensity.A quantitative correlation between the D index and ML intensity was observed within the same host crystal structure.This demonstrates that the D index is an effective indicator in material development to enhance ML intensity.The study revealed that when multiple host ion sites are available for the luminescence center, preferentially substituting the sites with a lower D index is crucial.This research provides valuable insights for developing high-performance ML materials.