Key Takeaways & Executive Findings
- •• • TS-FRET between BCA2PAM and R6G enables precise color tuning, with a 1 s delayed reappearance of 'appear' after UV off, providing a time-resolved encryption dimension that thwarts static counterfeit inspection. • • Laser power variation (high vs. low) on R6G-doped BCA2PAM films produces distinct visible patterns under UV and afterglow, allowing multilevel encryption; high-power QR codes are invisible under UV but emerge after breath exposure, offering humidity-triggered authentication. • • Integration with PDMS yields luminescent elastomers, and PET adhesive tapes create tamper-evident labels with customizable branding, demonstrating mechanical robustness and adaptability for industrial labeling. • • Rewritable capability: laser-written patterns visible under UV can be erased under ambient humidity and re-encrypted with new motifs, enabling reuse and reducing material waste in high-end anti-counterfeiting applications.
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Abstract
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.
1. Introduction
Polymeric multicolor afterglow materials offer tunable phosphorescence and superior processability compared to metal complexes and organic small molecules, but achieving precise color control and environmental stability remains challenging. Existing strategies, such as copolymerizing luminophores or incorporating multiple emitting centers, often suffer from complex synthesis and limited tunability. TS-FRET has emerged as a promising alternative, yet its integration with scalable patterning techniques for anti-counterfeiting has not been fully realized.
This study addresses the bottleneck by coupling TS-FRET with UV laser direct writing to fabricate phosphorescent labels. Using BCA2PAM as donor and R6G as acceptor, the authors achieve tunable afterglow and time-resolved multicolor displays. The method enables laser-engraved encryption with humidity-responsive and rewritable features, demonstrating a viable route for industrial anti-counterfeiting labels with multiple security levels.
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Xuhui Zhu, Jinting Huang, Yizhi Lin, Baoyu Wang, Shaolin Lu, Shuidong Chen, Zhaowei Lan, Dengchong Feng, Xirui Gu, Zetong Ma, Zhongke Yuan, Yuzhao Yang, Xudong Chen (2025). Laser-Engraved Multilevel Encryption Enabled by FRET-Based Tunable Multicolor Polymeric Afterglow Materials. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3540-y
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Frequently Asked Questions
What is the mechanism behind the time-resolved color change observed after UV irradiation?
The time-resolved color change arises from TS-FRET between the BCA2PAM donor and R6G acceptor. Upon UV excitation, the donor's triplet excitons transfer energy to the acceptor, resulting in delayed fluorescence. After UV off, the donor's long-lived phosphorescence dominates initially, but as the acceptor's delayed fluorescence decays at a different rate, the emission color shifts. The 'appear' pattern reappears after 1 s due to the persistence of the acceptor's emission, enabling temporal encryption.
How does laser power affect the encryption patterns and their visibility?
Laser power controls the degree of R6G doping and thus the FRET efficiency. High-power laser inscription creates patterns that are invisible under UV because the high acceptor concentration quenches donor emission, but become visible after breath exposure (humidity enhances FRET) and subsequent UV activation. Low-power laser inscription yields patterns visible under UV. This power-dependent behavior enables multilevel encryption.
What is the role of humidity in the encryption and erasure processes?
Ambient humidity plasticizes the polymer matrix, increasing molecular mobility and facilitating the diffusion of R6G or disrupting hydrogen bonds. This leads to erasure of laser-written patterns visible under UV, allowing re-encryption with new motifs. Conversely, breath exposure temporarily increases local humidity, activating hidden high-power laser patterns by enhancing FRET, as demonstrated by the emergence of QR codes.
How does the integration with PDMS and PET tapes enhance the material's applicability?
PDMS integration yields luminescent elastomers with mechanical flexibility, suitable for wearable or conformable labels. PET adhesive tapes provide a robust substrate for tamper-evident labels; the afterglow film adheres to the tape, and any attempt to remove it disrupts the pattern, revealing tampering. This combination offers customizable branding and practical deployment in high-end anti-counterfeiting.
What are the limitations regarding long-term stability and scalability of this encryption technology?
Long-term stability under varying humidity and temperature requires further optimization; the rewritable feature may degrade after multiple cycles due to material fatigue. Scalability is promising because laser writing is a mature industrial process, but uniform film fabrication over large areas and precise control of R6G doping remain challenges. Cost parity with existing anti-counterfeiting methods depends on the availability of BCA2PAM and R6G at scale.
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