Universal in situ supersaturated crystallization enables 3D printable afterglow hydrogel

Stretchable afterglow materials have garnered widespread attention owing to their unique combination of optical properties and mechanical flexibility. However, achieving a crystal environment to suppress the non-radiative transition of triplet excitons poses a challenge in constructing stretchable afterglow materials. Herein, we utilize an in situ supersaturated crystallization strategy to form afterglow microcrystals within a hydrogel matrix. This approach enables afterglow emission with a lifetime of 695 ms while maintaining high stretchability with tensile stress surpassing 398 kPa, extensibility over 400% and a high water content of 65.21%. Moreover, the universal supersaturated crystallization strategy allows for conferring tunable afterglow performance. Successful demonstrations in hydrogel 3D printing and anti-counterfeiting purposes showcase the potential for advanced applications of 3D printable afterglow hydrogels. This investigation provides guidelines for generally designing efficient afterglow hydrogels and addresses the inherent contradiction between flexibility and rigid in stretchable afterglow materials.