Tuesday , June 15 2021

Invisible Tags: Physicists at TU Dresden write, read and delete with light



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IMAGE: Luminescent label, non-contact printed on plastic foil. The light-emitting layer is thinner than human hair. The fingerprint can be deleted and replaced with another template.
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Sincerely, M. Gmelch and H. Thomas, TU Dresden

Prof. Rainecke and his team of LEXOS work with simple plastic films less than 50 μm thick, thinner than human hair. In these transparent plastic films they introduce organic fluorescent molecules. At first these molecules are in an inactive, dark state. By using ultraviolet radiation locally, it is possible that this dark state becomes active, fluorescent. By enhancing masks or laser writing, activated patterns can be printed on the film with a resolution that is comparable to ordinary laser printers. Like the stickers that glow in the dark, the patterns can be broadcast and the printed information can be read. By illumination with infrared light, the tag is completely erased and new data can be recorded.

The principle of operating these programmable transparent labels is based on the well-known oxygen molecule. Oxygen is present in the plastic film and steals the light energy from the glowing molecules. Ultraviolet radiation causes a chemical reaction that effectively removes oxygen from the layer. As a result, fluorescent molecules are activated and can emit light. The infrared light deactivation process is based on an increase in foil temperature, which leads to increased oxygen permeability and therefore recharging of the oxygen layer.

These new labels can be produced in any size. The low cost of materials of less than 2 euros per square meter promises a wide range of possible applications: Information such as barcodes, serial numbers or addresses can be hidden only for on-demand reporting. Also, these invisible tags can drive document security and counterfeiting to a whole new level.

Prof. Rayneket thinks further: "These invisible and overwritten labels can be used in many ways. We can produce labels thinner than conventional barcode stickers. These labels can become a universal alternative to very often technology-intensive solutions for sharing information in our daily lives. These fluorescent markers make the electronics obsolete at the place where the information is stored. The development and optimization of such systems opens up a broad research area that combines material development, technological engineering and fundamental research in an interdisciplinary way.

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Original publication: M. Gmelch, H. Thomas, F. Fries, S. Reineke, Programmable transparent organic luminescent labels. Sci. Adv. 2019; 5: eaau7310.

For the group of light emitting and excitonic organic semiconductors (LEXOS):

The LEXOS Group is part of the Integrated Center for Applied Physics and Photonics in Dresden (IAPP) and the Institute of Applied Physics of the Technical University of Dresden, led by Prof. Sebastian Reinecke. One of the highlights of the LEXOS Group is the study of exciton and luminescent systems, covering organic and other related materials. The group has strong experience in optical spectroscopy of such systems. One such example is the study of organic biluminiscent, where the luminescents exhibit fluorescence and phosphorescence at room temperature. In addition, the LEXOS Group has many years of experience in research and development of organic LEDs (OLEDs). This OLED study includes the development of stacks and concepts, device optics, charge transfer and recombination studies, long-term stability studies, material development (additives and emitters) and device integration.

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