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Printed Electronics World
Posted on May 13, 2007 by  & 

Improvements in AC Electroluminescent Displays

AC Electroluminescence ACEL - Now Seeing Rapid Evolution

At the recent IDTechEx Printed Electronics Europe conference in Cambridge UK it was clear that one of the oldest laminar display technologies - ac electroluminescence ACEL - is now seeing rapid evolution. Pelikon, having won the prize for the best device improvement with a version that works in bright light, presented on the first mass produced ACEL displays. elumin8 presented on its startling wide area, flexible EL displays up to 50 meters long and enormous hanging art works.
Pelikon now employs contrast enhancement layers. The companies use different phosphors and different numbers of layers of the screen printed inorganic construction but they have a basic structure that is similar and being improved by a stream of better materials and assembly concepts. Indeed more is to come because the nanomaterials developers are now involved as is Kodak European Research which presented on its improvements to both ACEL and OLED colours, the present EL limitations being seen as:
  • best performing phosphors lie in the green/blue output region
  • no adequately comparable red or orange phosphors.
  • (lifetime x brightness) performance less than OLED, (typically about 3000hr for 100cd/m2)
  • Colour-by-RGB, -W and -RGBW are all difficult to achieve.
Kodak gave a practical demonstration of colour-by-green-blue around screen-printed ACEL lamps donated by Pelikon and using Sylvania phosphor, 165V @ 500Hz,1.5kHz & 5kHz (other popular EL phosphors include Cu doped ZnS from DuPont). Kodak explored a red conversion strategy by separate underlayer (vs. dye incorporation in dielectric binder, or shelling phosphor), with an RGB colour filter array constructed using Kodak DuraClear, a product designed for backlit displays using a stable photographic dye set, and manipulating overall colour positions with help of a proprietary modelling tool. The alternative colour architecture for EL displays with the advantage of identically driven pixels was demonstrated. It is particularly suited to EL using ZnS-based phosphors. Kodak achieved straightforward colour balancing and gamut adjustment to acceptable standards. This development is not mainstream to Kodak, but the company suggests that its (lifetime x brightness) vs. cost trade-off might be of interest to other potential partners.

Meanwhile, the Pelikon products have progressed as follows:

Source Pelikon
Pelikon exhibited its prize winning fashion watch and its intuitive flexible touch displays, a huge advance on LCDs and other human interfaces.
Source Pelikon
There is much more to come from these highly innovative companies and the increasing number of developers of EL materials. Pelikon shared its future timelines as follows.
Source Pelikon
More will be revealed at the world's largest printed electronics conference Printed Electronics USA San Francisco 12-15 November 2007 - where there will be at least 500 delegates, visits to six local facilities and four optional Masterclasses. Contact Chris Clare for more details at
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