Dual mode chameleon d-f heterometallic nano-MOFs for anti-counterfeiting applications

Widespread forgery in many sectors, ranging from currency, legal documents, electronics, car parts, or pharmaceuticals, has become a real threat to the society. [1] The immense number of counterfeited products can be linked to the recent development of high-resolution equipment, such as digital cameras, printers and scanners. Counterfeiting products not only infringe the rights of copyright owners, but they also cause extensive damage to the society by reducing the value of money or for example by causing health issues (e.g. through falsified pharmaceuticals). The use of fluorescent anti-counterfeit technologies, including lanthanide luminescence has already been illustrated by the red and green emitting materials in Euro banknotes that light up when placed under a UV lamp. [2] In Euro banknotes the emission of two different colors is observed when the banknotes are placed under a UV lamp. The specific narrow-line emission color of the lanthanides is very difficult to mimic when no information is available on the exact identity of the luminescent material in the banknote. However, the emission of the two different colors can be mimicked by using other materials than lanthanide compounds. Therefore, it is no surprise that Euro banknotes have been quite successfully falsified multiple times. In our work we have studied the design of dual mode anti-counterfeit materials based on d-f heterometallic nano-MOFs. We have created a single material, which strongly emits two different colors at wavelengths well matched to the standard UV lamps. What is more we have added an extra feature based on temperature dependent luminescence, which will increase the security level significantly. The double stage coding capability of these nano-MOFs would make the materials almost impossible to falsify. Nano-MOFs have been chosen for this application due to their unique luminescence properties. The nano-size of the MOFs is crucial for further processability, such as the creation of security inks, which can then be printed onto various surfaces. References [1] L. Li, Bus Horizons 2013, 56, 167-177 [2] https://www.ecb.europa.eu/euro/html/security_features.en.htm