Professor Reineke and his Lexos team work with plastic foils of 50 micron thickness into which they introduce organic luminescent molecules.
Initially these molecules are inactive and dark but by using ultraviolet radiation it is possible to activate the molecules into a luminescent state. The use of mask illumination or laser writing allows patterns to be written to the foil on a resolution comparable to laser printers. Infrared light is used to erase the tag and return it to the dark state.
Luminescent tags can sustain multiple writing, reading and erasing cycles. The UV-illuminated patterns can be erased by infrared light. Source: TU-Dresden
The working principle of the tag foil is the migration of oxygen atoms that suppress luminescence. Ultraviolet radiation induces a chemical reaction that removes inhibiting oxygen from the luminescent layer. The deactivation process using the heat of infrared light to raise the temperature of the foil, leading to an increased oxygen permeability and therefore a refilling of the luminescent layer with oxygen and switching off the effect.
The material costs less than €2 per square meter and could find use for on-demand variable signage, document security and anti-counterfeiting measures.
Programmable transparent organic luminescent tags was published in the online journal online journal "Science Advances"
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