Quantum technology rocks the video display world

March 31st, 2017, Published in Articles: EE Publishers, Articles: EngineerIT


The quantum dot TV display at the 2017 Samsung Africa Forum.

At one stage producers of television sets focussed their research and manufacturing capabilities on organic light-emitting diodes (OLEDs) to produce the perfect TV picture and images on hand-held devices, but with the announcement  of quantum dot technology that focus has fast shifted. At the Samsung Africa Forum 2017 held during February in Cape Town the major focus was on QLED televisions based on quantum technology where colours displayed are brighter and where black is  blacker than black.

Towards the end of 2016 Samsung acquired QD Vision, the US-based provider of quantum dot technology for consumer displays. The company has been heavily pushing quantum dots in their newest televisions in order to increase their colour scope without having to make use of multi-colour LEDs back lighting. The LEDs in most LCD LTVs emit white light, but those in quantum-dot televisions emit blue light. Both types actually use blue LEDs, but they’re coated with yellow phosphor in normal LCD televisions and thus emit white light.

Quantum dots can be arranged along the entire back of the display in a film insert or in a “quantum rail” alongside an edge-lit system. Here’s where the quantum dots come in. The blue LED light drives the blue hues of the picture, but red and green light is created by the quantum dots. The quantum dots are either arranged in a tube — a “quantum rail”— adjacent to the LEDs or in a sheet of film atop the light-guide plate.

Quantum dots have one job, and that is to emit one colour. They excel at this. When a quantum dot is struck by light, it glows with a very specific colour that can be finely tuned. When those blue LEDs shine on the quantum dots, the dots glow with the intensity of fireflies.

Quantum dots are tiny, and their size determines their colour. There are two sizes of dots in these TVs. The “big” ones glow red, and they have a diameter of about 50 atoms. The smaller ones, which glow green, have a diameter of about 30 atoms. There are billions of them in a quantum-dot TV. If quantum-dot light is observed with a spectrometer, a very sharp and narrow emission peak will be seen. Pure red and pure green light travel with the blue light through the polarisers, liquid crystals, and colour filters.

Quantum dots have an advantage over traditional LCD TVs when it comes to vivid hues and colour spectrum. In a normal LCD, white light produced by the LEDs has a wider spectrum. It’s kind of dirty, with a lot of light falling in a colour range unusable by the set’s colour filters.

A filter is a very lossy device. When you purify the colour using a colour filter, then there is practically no transmission through the filter. The purer the colour started with, the more relaxed the filter function can be. That translates directly to efficiency. So with a quantum-dot set, there is very little wasted light. It will deliver brighter, more-saturated, and more-accurate colours. These sets also run cooler, consume less energy and can be mounted flush against a surface.

The word quantum attracts attention. Largely because of its association with quantum mechanics. Quantum dots are crystal semiconductors measuring just a few nanometers in width. Hit these nanocrystals with light, and they emit coloured light in strict correlation to their size.

Nanotechnology is manipulation of matter on an atomic, molecular, and supramolecular scale. Many types of quantum dots will emit light of specific frequencies if energy or light is applied to them, and these frequencies can be precisely tuned by changing the dots’ size, shape and material, giving rise to many applications.

Quantum dots optoelectronic properties change as a function of both size and shape.  Larger QDs (radius of 5 – 6 nm, for example) emit longer wavelengths resulting in emission colours such as orange or red. Smaller QDs (radius of 2 – 3 nm, for example) emit shorter wavelengths resulting in colours like blue and green, although the specific colours and sizes vary depending on the exact composition of the QD. Because of their highly tuneable properties, QDs are of wide interest. Additionally, their small size allows for QDs to be suspended in solution which leads to possible uses in inkjet printing and spin-coating.

Samsung’s new design replaces red, green and blue colour filters with segregated stacks of quantum dots, which shine pure red, green and blue when exposed to a blue LED backlight. The colours you see are no longer filtered, they’re directly emitted, similar to an OLED or plasma display. A conventional LCD panel must still act as a grid of shutters behind these quantum dots to selectively block light from reaching them — that’s how black is produced. Pixels cannot be individually switched off — a property of OLED panels that produces their outstanding black levels. But Samsung says there’s still an advantage: Because quantum dots are activated to glow by blue LED lights instead of yellowish-white ones, any “leaking” light will be toward the outer edge of the visible spectrum, which humans are less perceptive to. Samsung claims that this should cut down on the nasty “halo” and “light blooming” effect.

Quantum dot display technology has only be around for a few years and from what has been seen many more development in TV and display panels using this technology are likely to hit the market at regular intervals. Samsung at their QD technical briefing at Africa forum said “Watch our space”.

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