Plastic luminescence in mechanoluminescent composites

Mechanoluminescence (ML) materials are a novel class of substance that emit light in response to mechanical stimuli. When combined with other materials, their luminescence mechanisms remain unclear, especially during irreversible plastic deformation. In this study, an ML material [(3ZnS/2CaZnOS) 0.98 SrZnOS 0.02 :2%Mn 2+ ] was developed and incorporated into epoxy resin to fabricate ML-composite cubic, cylindrical, and spherical specimens. Plastic luminescence of the ML composites was observed after yielding in uniaxial compression tests. Supported by numerical simulations, a strong correlation between luminescence intensity of ML composites and plastic strain was revealed. This indicates that plastic deformation was found to be closely associated with the observed luminescence of homogeneous ML composites. In more complex granular systems, ML-composite particles were synthesized for compression and ring-shear experiments. The results demonstrated that the interparticle frictional slip, a general form of plasticity in granular assembly, coincided with the recorded luminescence. These findings provide critical insights for the luminescence in ML composites during the plastic stage.