Direct recording and reading of mechanical force by afterglow evaluation of multi-piezo mechanoluminescent material Li0.12Na0.88NbO3 on well-designed morphotropic phase boundary

Mechanoluminescence (ML) refers to the photon emission from materials subjected to mechanical stimuli. A general concept concerning ML materials is that they cannot directly record a stress history (mechanical record; MR). Here, we report an approach that retrieves a quantitative recording of stress history through the afterglow characteristics analysis of a specific multi-piezo ML material Li0.12Na0.88NbO3:Pr (LNNO), which has been designated to exist near the structural phase boundary of rhombohedral R3c and orthorhombic P21ma. Contrary to the general expectation that the afterglow characteristics are irrelevant to mechanical loading history, LNNO was strongly correlated with the stress distribution after UV excitation. This enabled us to read the recorded stress precisely from the afterglow image of the material. Furthermore, the spatial distribution of the MR was also realized, showing the capability of the readout of stress history in both time and space. This unusual MR function is attributed to eliminating shallow trap sites, which affected the afterglow characteristics upon applying mechanical load.