Quantum dots make it possible to display any color in full brilliance. Credit: © Fraunhofer IAP
Quantum dots have made it possible to substantially increase color quality in LCD displays. However, these cadmium-based nanocrystals have proven to be harmful to the environment. Researchers are now developing a promising alternative: quantum dots based on indium phosphide.
The landscape is breathtaking. Because it is so real, you forget for a moment that the eagle circling the sky is not outside your window, but is instead on your television. Such realistic images are not only due to high resolution displays; the colors play a role as well. This is possible thanks to quantum dots (QDs), with a thickness of a few atoms. These nanoparticles located in the backlight units of QD LCD displays offer a cornucopia of colors, but also they possess another extraordinary characteristic. “One big advantage of quantum dots is that their optical properties can be selectively modified by changing their size,” explains Dr. Armin Wedel of the Fraunhofer Institute for Applied Polymer Research IAP in Potsdam, Germany. “This means you no longer have to manufacture 3 separate materials for the colors red, green and blue; now it is possible to do the job with just one.” This saves both time and money.
At sizes > 2nm, the color changes to green. The largest of the quantum particles, at 7nm in size, emit within the red spectral range. Currently, Wedel and his team are developing quantum dots for display backlighting on behalf of Dutch company NDF Special Light Products B.V. These quantum dots will improve the color rendering and color realism of the displays. Here, the crystals are manufactured for the different emission colors and embedded in plastics. These plastics are subsequently processed into films and built into the display as a conversion film.
With this task, researchers are facing a new challenge. The EU Commission is currently considering a ban on cadmium in consumer goods by 2017, because of its damaging effect on the environment. However, it is also considered to be the ideal material for manufacturing the crystals – cadmium-based quantum dots can achieve a narrowband spectrum sharpness of just 20 to 25 nanometers. Display manufacturers around the world are now looking for suitable replacement materials with similar characteristics. Against this backdrop, Fraunhofer IAP looks to be on a promising path.
“We are testing quantum dots based on indium phosphide together with NDF Special Light Products,” says Wedel. His team has already managed to achieve a spectral sharpness of 40 nanometers. “We see this as a good first milestone, but we are still striving for further improvement,” says Wedel.
APPS: TV, medical or aeronautical equipment displays. Furthermore, quantum dots can also increase the efficiency of solar cells, or can be employed in bioanalytics. For such special cases, the optical characteristics of the quantum dots must be precisely configured to the specific application requirements. http://www.fraunhofer.de/en/press/research-news/2015/october/brilliant-colors-from-environmentally-friendly-crystals.html
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