Carbon dots for epoxy curing: Anti-forgery patterns with long-term luminescent stability

• Epoxy monomers were cured by CDs alone to produce luminescent epoxy resins. • The photoluminescent properties of CDs in the epoxy were preserved over 8 weeks. • Epoxy curing by CDs was used for stealth patterning for anti-forgery applications. Here, we demonstrate that pristine CDs, obtained from amine-containing precursors, were available for the curing of epoxy monomers. The optical properties and the surface chemical functionality of the CDs depended on the nature of the precursors. The CDs showed good compatibility with the epoxy monomer before and during the curing reaction, which led to their uniform dispersion in the epoxy matrix. In addition, it was found that the direct growth of the epoxy chains on the CD surface led to the effective passivation of the CDs. The CD/epoxy nanocomposites showed retentions of more than 80% in PL intensity even after 8 weeks of storage in ambient conditions. Together with those beneficial properties, the CD/precursors were readily patterned or printed on various substrates. The chemical components of the luminescent CDs are similar with the epoxy matrix and furthermore are common in various organic substrates, prohibiting reverse engineering. The combination of the CD/epoxy resin showed strong potential for stealth patterning and printing to enhance anti-forgery protection. Importantly, the use of CDs as curing agents can be further extended to other various kinds of resins.