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Low-cost upconversion nanomaterials for anti-counterfeiting solutions
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This work consisted on the production and characterization of low-cost upconversion (UC) nanoparticles based on zirconia oxides (ZrO2). The production was made by a hydrothermal process assisted by microwave irradiation, where 4 reagents were tested: sodium hydroxide, hexamethylenetetramine, urea and ethylenediamine. Ytterbium (Yb) and erbium (Er) were used as dopants to allow the upconversion process. The aim was that the nanoparticles would match photoluminescent characteristics of a detector provided by INCM (Imprensa Nacional – Casa da Moeda) so that it can be used as a security marker.
Hexamethylenetetramine has proven to be the best reagent to reach the desired nanoparticles with a maximum size of 100 nm. It was concluded that no dispersant was necessary to stabilize the powder when added directly into the proper ink. Different synthesis parameters were tested to optimize the morphology and size of nanomaterials such as time, pH and temperature. It was also achieved the scale up production of this nanoparticles, since passing from 25 ml to 600 ml solutions did not alter the optical response. Both flexographic and screen printing were proven successful printing methods as the final luminescent outcome matched the marker characteristics. A cheaper, environmentally friendly and new marker was accomplished, allowing that more products may have a security mark, guaranteeing their final authenticity.
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upconversion ZrO2 ytterbium erbium microwave security marker