Accessing Excitation‐ and Time‐Responsive Afterglows from Aqueous Processable Amorphous Polymer Films through Doping and Energy Transfer

Abstract Smart afterglow materials in response to excitation and delay time, including crystals, polymeric films, and carbon dots, have attracted considerable attention on account of their fundamental value in photophysics and promising applications in optoelectronics. However, the fabrication of amorphous and flexible polymer films with fine control remains underexplored. Herein, new doped polymer films based on sodium alginate and aromatic carboxylates are developed, which demonstrate following advantages: (i) easy and fast fabrication through the aqueous solution process, (ii) flexible, transparent, and re‐dissolvable characteristics, (iii) multi‐tunable afterglow colors from blue to red and even white with fine control. Specifically, even better controllability can be achieved through co‐doping and triplet‐to‐singlet Förster resonance energy transfer (TS‐FRET). Multimode advanced anti‐counterfeiting of these materials is demonstrated using their excitation‐ and time‐dependent as well as TS‐FRET‐mediated afterglow colors.