ELECTRONIC displays that can be printed onto virtually any surface, including paper and fabric, are now a step closer, thanks to the creation of a light-emitting ink.
A team at in Tokyo, Japan, has used a conventional screen-printing technique to deposit a thin layer of the ink, a luminescent gel, onto a surface. The gel consists of a ruthenium compound that emits a bright light when a voltage is applied to it, along with an electrolyte and silica nanoparticles.
“The ink holds a compound of ruthenium that emits a bright light when a voltage is applied across it”
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The electrolyte is a liquid salt, an ionic liquid which does not easily evaporate. It also prevents the ink from degrading, allowing displays to be printed onto surfaces without the need for a protective coating. The ink will not wash off in water, making it suitable for use with textiles. Meanwhile, the silica nanoparticles blend with the light-emitting liquid to form a gel, allowing it to be printed onto different surfaces in discrete blobs, to form pixels.
So far, the ink is only able to emit reddish hues when activated, although the researchers are working on other metal compounds that emit green and blue light, to eventually give them the whole spectrum.
The screen-printing technique allows only rough pixels to be generated, and so the images produced currently are fuzzy. The team is developing techniques to deposit the gel onto surfaces using an ink-jet printer, which would allow them to create smaller pixels and hence higher resolution. Ink-jet printing is also much cheaper than the lithographic techniques used to build digital displays.
The company hopes to market the technology within five years and reckons it could be used to make light-emitting posters, clothing, flexible displays and new lighting applications.
