Sustainable Long‐Living Afterglow From a Natural Polyphenol Embedded in Urea‐Formaldehyde Resin

Room-temperature phosphorescent (RTP) materials have attracted considerable attention for optoelectronics and anti-counterfeiting, but developing sustainable, high-performance RTP systems from natural resources remains challenging. Here we report a strategy to achieve long-lived afterglow by embedding ellagic acid (EA) into a urea-formaldehyde (UF) resin matrix. The EA/UF composite exhibits green RTP emission with a lifetime of 984.2 ms. Mechanistic studies reveal that the restricted carbonyl moieties of EA and the formation of a compact crosslinked network with UF promote spin-orbit coupling and stabilize triplet excitons. By incorporating rhodamine B (RhB), red afterglow was achieved through a triplet-to-singlet Förster resonance energy transfer (TS-FRET) mechanism. This strategy is universal: tannic acid, gallic acid, caffeic acid, and vanillic acid can all be converted into afterglow RTP materials in the UF matrix. As proof-of-concept, EA/UF was used for latent fingerprint imaging, time-resolved anti-counterfeiting, and 3D shaping. This work provides a sustainable platform for activating long-lived afterglow RTP from renewable natural polyphenols.