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Optoelectronics/Displays  

Quantum dots spray LCD screens with more vibrant colours

Posted: 11 Aug 2014  Print Version  Bookmark and Share

Keywords:quantum dot  LCD 

High-tech specks known as quantum dots are capable of enhancing even the most advanced LCD screens available in the market today. A scientist who works at 3M will describe a quantum dot enhancement film (QDEF) technology—which claims to bring brighter, more vibrant colour to mass market TVs, tablets, phones, and other displays—at the 248th National Meeting & Exposition of the American Chemical Society (ACS), taking place in San Francisco today through Thursday.

"Green grass just pops out at you from these displays," says Eric Nelson, Ph.D., who helped create the plastic films that hold the quantum dots in a screen. "We believe this is the most efficient way to get to a high-colour display."

That's because quantum dot, or "QD," displays need less energy compared to other high-colour options. QDs are superconducting crystals so small that 10,000 could fit across the width of a human hair.

Almost all electronics sold today, from TVs to smartphones, use LCDs. A typical LCD works by shining white light through a series of filters that produce the colours the viewer sees. To achieve the best colour, these filters need to be fairly dark. However, it takes a lot of energy to make the light bright enough for the viewer's eye. The other problem, says Nelson, is that "you always tend to leak a bit of green into red, and blue into green, and so forth. So instead of ending up with a very pure red, you end up with an orange-y colour. It's difficult to get roses or apples to look very red on a conventional LCD."

A colourful approach

Rather than filtering light, QDs change it into a different colour. The dots—made for 3M by Nanosys, Inc.—produce specific colours of light based on how big they are. In 3M QDEF displays, the LCD's white backlight is replaced with a blue one, and a sheet of plastic embedded with QDs that produce red and green light is placed over it. The display combines these three colours to produce all the colours the viewer sees.

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Quantum dots make greens and reds pop on screens (left) compared with other types of displays (right). Source: 3M

One drawback of the dots is that they break down quickly when exposed to water and oxygen in the air. To address this challenge, Nelson helped create the plastic sheathing that protects them. They sandwiched the QDs between two polymer films, with the QDs embedded in epoxy glue. "The polymer/quantum dot sandwich looks like a piece of plastic film," says Nelson. Coatings on the film provide further protection and enhance the viewing experience.

Nelson also will describe the environmental advantages of the technology. Because the QDEF displays need less light, they consume less electricity and help device batteries last longer than other high-colour solutions. He says 3M's tests have shown that the dots' heavy metals—many of which are already found in today's electronics—are entirely sealed inside the film. That means they won't leach out during the products' lifetime or as they languish in landfills if the displays aren't recycled.

GE ups colour vibrancy in LEDs with phosphor powder
The use of the PFS phosphor in LED systems generates a reddish colour that is sharper, cleaner and truer compared to nitride phosphor—resulting in less colour bleed and a richer picture in displays.

3M hopes QDEF technology will compete well with more costly displays like those that use organic light-emitting diodes (OLEDs). Nelson explains that OLEDs produce similarly brilliant colours to the QDEF displays, but they use individual lights to make different colours. The drawback to OLEDs is that they are much more costly to manufacture.

Although QDEF displays are more expensive than conventional low-colour LCDs, Nelson says the cost will come down as the technology becomes more widespread and as manufacturing costs come down with increased production scale. Several devices featuring QDEF are already on the market, and more are on the way.





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