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Electroluminescent yarn lights the way

06 Nov 2007

A team at the University of Manchester has produced yarns based on thin-film electroluminescent technology that emit light when powered by a battery.

"To the best of our knowledge this is a new development," Tilak Dias of the university's William Lee Innovation Centre (WLIC) told optics.org. "The luminence of a single strand of our electroluminescent (EL) yarn is greater than that of photoluminescent glow yarns, currently used in high visibility applications."

The yarns are based on commercially available conductive yarns, onto which carefully chosen polymer layers are added. The team is currently using silver-coated nylon, although yarns based on polyethylene monofilaments with a carbon core have also been tested.

"We apply one to two nanolayers of a dielectric polymer in such a manner that an extremely thin and flexible layer is created around the silver surface of the core yarn," explained Dias. "On top of the dielectric layer, a polymeric layer embedded with EL particles such as phosphors is applied. The structure is then covered with a layer of conductive transparent polymer."

The different polymer layers create a textile capacitor, with the EL particles trapped between two electrodes. The conductive core forms one electrode, while the other is the conductive transparent layer. When the yarn is powered, the resultant electric field causes the electroluminescent coating to emit light.

"The textile characteristics of the core yarn are maintained, so they can be processed into fabric structures using current manufacturing techniques," said Dias. "At the moment our material is less flexible than conventional yarns, although more flexible than current optical fibers that are incorporated within fabrics to provide illumination," commented Dias. "But EL yarn can easily be incorporated into a knitted or woven fabric to provide illumination when it is powered."

To date the team has produced prototype yarns to demonstrate the feasibility of the technology, and will now work on optimization and scaling-up for commercial applications.

"In our opinion the first applications will be in automotive and industrial textiles," commented Dias. "Imagine the entire interior of your car boot or the whole cabin of your car lighting up, or the ceiling of a board room. Applications in the garment sector will come later."

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