The limitation lies in that efforts to tune the reflection color of luminescent materials by modifying inherent chemical structures would inevitably change the fluorescence properties at the same time, because both of them are determined by the molecular structures (organic) or energy level structures (inorganic) of the pigments. Although researchers have reported plenty of paradigms to tune the fluorescence for encoding intricate information, it is a great challenge to arbitrarily program the reflective patterns while maintain the integrity of the fluorescent patterns, and vice versa. If both reflection and fluorescent colors are simultaneously programmed to design a geminate label, which is capable of demonstrating entirely different information in reflective and fluorescent states, the reflection color will also be adopted to offer more optical states for carrying information, thus enhancing the anti-counterfeiting level of the security labels. As another color of the inks, reflection color arising from the selective absorption of visible light by pigments (pigment color), however, has rarely been taken into consideration in security labels with fluorescent color. To this end, researchers strive to develop novel inks of luminescent materials as carriers of authentic messages, including lanthanide-doped nanoparticles, semiconducting quantum dots, organic dyes, and metallic nanoparticles, by tuning fluorescent color, intensity, and lifetime value 3, 4, 5, 6, 7, 8, 9. The cutting edge in the development of next-generation anti-counterfeiting technologies currently focuses on designing security inks that are able to offer numerous optical states to convey distinct information. Such two-tone inks have enormous potential to provide a platform for encryption and protection of valuable authentic information in anti-counterfeiting technology.Īnti-counterfeiting technology, in which security labels are popular elements for protecting authentic articles, is of significance to help companies, customers and governments reduce economic loss threatened by counterfeit goods in paper currency, medicine, edible, clothing, and microelectronics 1, 2. These structurally defined microdroplets fabricated by a capillary microfluidic technique contribute to different but intact messages of both reflective and fluorescent patterns in the geminate labels. Here, a strategy is reported to design geminate labels by programming fluorescent cholesteric liquid crystal microdroplets (two-tone inks), where the luminescent material is ‘coated’ with the structural color from helical superstructures. Efforts to tune the reflection color of luminescent materials by modifying inherent chemical structures remain outweighed by substantial trade-offs in fluorescence properties, and vice versa, which destroys the information integrity of labels in either reflection or fluorescent color.
Creating a security label that carries entirely distinct information in reflective and fluorescent states would enhance anti-counterfeiting levels to deter counterfeits ranging from currencies to pharmaceuticals, but has proven extremely challenging.
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