Development of luminescent forensic security materials utilising ionic liquid technology Anthony Fitzpatrick Nottingham Trent University, UK Counterfeiting money has existed for as long as money has been in use. However, gone are the days of shaving coins or engraving a printing press, as modern technologies like digital printing and graphic arts have made it easier to forge items like banknotes and important documents. Therefore, features based on molecular properties that can be verified in a short space of time are integral to increasing the security needed to easily identify counterfeit materials. 1 Formulation of luminescent composite materials is a challenge in the security industry, banknote fabrication in particular, consists of multiple chemical processes to embed security features. The solubility of novel luminescent complexes and material stability are two components that can make or break a new compound going to market. Ionic liquids being a class of materials that exist as a liquid but only consist of a positively charged species (cation) and a negatively charged species (anion) without the need for a solvent inherently overcome these issues of solubility. 2,3 These functional liquids can then be mixed with ease to form novel photo responsive materials. We have investigated fabrication of ionic liquid composite materials based on lanthanide coordination complexes, to cover both the visible and near infrared emission wavelengths, for use in security inks aimed at application in banknotes, food security and raw materials labelling. This has resulted in stable luminescent materials that give spectral features much harder to counterfeit or fake.
Figure 1: (Left) Luminescent ionic liquid materials under shortwave UV light. (Right) €10 banknote under shortwave UV light. References 1. H. Wang and L. Sun, Acc Mater Res, 2021, 2, 1–6. 2. T. Endo, K. Sunada, H. Sumida and Y. Kimura, Chem Sci, 2022, 13, 7560–7565. 3. D. Prodius and A. V. Mudring, Coord Chem Rev, 2018, 363, 1–16.
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