Temporal pattern of the mechanoluminescent lighting from impact-loaded ZnS ceramics

Mechanoluminescence (ML) from deformed ductile materials is caused by sliding of charged dislocations. The main source of the ML in loaded brittle solids is the interatomic bond breakage. In this work, the ML from impact damaged ductile ZnS ceramics was studied. It was revealed that the time series of ML pulses exhibited two well-separated peaks. A two-stage ML excitation of this kind in ZnS ceramics was observed when the applied load exceeded an ultimate plastic deformation. The positions of each peak along the time axis were found to be dependent in different ways on physical and mechanical properties of crystallites that constituted the given ceramics. The investigated ceramics were produced by four different technological methods. The obtained samples differing in the dimensions of grains and separation of grain boundaries were tested. The statistical analysis of a temporal pattern of the ML lighting showed that the mechanisms of excitation of the two peaks were not the same. The first ML peak was assigned to the plastic deformation preceding the ceramics cracking. The second peak originated from the interatomic bond breakage in nucleated and growing cracks.