Structure-dependent mechanoluminescence behaviors via 3D printing of capillary suspensions

Mechanoluminescence (ML) materials have received considerable attention due to their ability to transform mechanical stimuli into optical signals. However, the potential of ML devices has not been fully leveraged as restricted by the relatively simple geometry design, which inherently limits the programmability of the luminescence behaviors and mechanical properties. Here, we present a design strategy and fabrication technique for creating well-defined periodic cellular 2D or 3D ML devices with tunable mechanical properties and structure-depended ML behavior (i.e., anisotropic and isotropic luminescence). A granular ink formulation consisting of zinc sulfide (ZnS)-based phosphors and elastomer precursors is developed to enable 3D printing by taking advantage of the capillary state. The quantitative structure-stress-luminescence relationship is further studied, which provides fundamental knowledge support for designing next-generation ML-based stress sensors and wearable devices.