Laser-Engraved Multilevel Encryption Enabled by FRET-Based Tunable Multicolor Polymeric Afterglow Materials
Polymeric multicolor afterglow materials with tunable phosphorescence and environmental adaptability remain a bottleneck in optical anti-counterfeiting. This work integrates triplet-to-singlet Förster resonance energy transfer (TS-FRET) with ultraviolet (UV) laser direct writing to fabricate phosphorescent anti-counterfeiting labels. Using poly(acrylamide-co-4'-vinyl-[1,1'-biphenyl]-3,5-dicarboxylic acid) (BCA2PAM) as the donor and rhodamine 6G (R6G) as the acceptor, precise color tuning is achieved. Time-resolved multicolor displays are realized by loading afterglow materials onto filter paper, while luminescent elastomers are synthesized via integration with polydimethylsiloxane (PDMS). Laser inscription of 'disappear' on R6G-doped BCA2PAM films at varying laser powers yields exclusive visibility of 'appear' under UV irradiation; upon UV off, 'disappear' emerges, followed by reappearance of 'appear' after 1 s, demonstrating encryption efficacy. High-power laser-inscribed QR codes remain imperceptible under UV but become visible after simulated breath exposure and subsequent UV activation. Integrated with polyethylene terephthalate (PET) adhesive tapes, the films form tamper-evident labels with customizable branding. Laser-written patterns visible under UV can be erased under ambient humidity and re-encrypted with new motifs, exhibiting rewritable capability. These results provide a new method based on ultraviolet light and multicolor time-resolved coupling in optical encryption, demonstrating industrial production potential for high-end anti-counterfeiting labels.