Quantum Dot LCD Technology
The first thing to know is quantum-dot displays are a new type of LED-backlit LCD. The image is created just like it is on an standard LCD screen, but quantum-dot technology enhances the colour.
On an LCD, you have the backlight system, which is a bank of LEDs mounted at the edge of the screen or immediately behind it. The LED light is diffused, directed by a light-guide plate and then beamed through a polarized filter. The photons then hit a layer of liquid crystals that either block the light or allow it to pass through a second polarized filter.
How a Nanosys quantum-dot film sheet (QDEF) fits into an LCD display.
Before the light gets to that second polarizer, it passes through a layer of red, blue, and green (and sometimes yellow) colour filters. These are the sub-pixels. Electrical charges applied to the sub-pixels moderate the blend of coloured light visible on the other side. This light mixture creates the colour value of each pixel on the screen.
With a quantum-dot display, there are no major changes to the manufacturing process. The same design issues also still apply. You can have full-array backlit quantum-dot sets with local-dimming technology (Good for image uniformity and deeper blacks). There can be edge-lit quantum-dot sets with no local dimming (Thinner, but you may see light banding and greyer blacks). You can have 1080p quantum-dot sets, but you’re more likely to see only 4K quantum-dot sets because of the industry’s big push toward UltraHD/4K resolution.
The manufacturer of Quantum Dot Enhancement Film Nanosys, provides optical film components for LED driven LCD displays. Each sheet of QDEF contains trillions of tiny Quantum Dot Phosphors of different sizes. Larger dots emit longer wavelengths (red), while smaller dots emit shorter wavelengths (green).
During fabrication, the Quantum Dots are tuned to create better colour by changing their size to emit light at the correct wavelengths. Traditional light emitting materials such as crystal phosphors have a broad fixed spectrum. Quantum dots can convert light to nearly any colour in the visible spectrum, giving display designers the ability to tune and match the spectrum more accurately to colour filters while improving energy efficiency. Designed to replace the functionality of a diffuser sheet while actively converting colour, QDEF can be added to an LCD's film stack with little change in overall thickness or manufacturing process.
Differences in Quantum-Dot LCD Manufacture
In a quantum-dot display, the changes start with the colour of the backlight. The LEDs in a standard display emit white light, while those in a quantum-dot display emit blue light. Both types actually use blue LEDs, but they are coated with yellow phosphor in a standard display and therefore 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.
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 on top of the light-guide plate.
Blue is the highest-energy portion of the spectrum, much greater than red or green. The blue high energy light is refracted to a lower energy state to create the red and green colours.
If observed with a spectrometer, quantum-dot light gives a very sharp and narrow emission peak. Because of this, quantum dots have an advantage over a standard LCD display when it comes to vivid hues and colour gamut. In a standard LCD display, the white light produced by the LEDs has a wider spectrum, with a lot of light falling in a colour range unusable by the displays colour filters.
With a quantum-dot display, there is very little wasted light producing a display with brighter, more-saturated and more-accurate colours.
Manufactures of Quantum Dot Technology
At this stage, three companies are the big players in the quantum-dot manufacture.
QD Vision specializes in glass-tube “edge-lit” components, and its systems can be found in TCL TVs and monitors from Philips and AOC.
Nanoco focuses on cadmium-free, film-based quantum dot systems. They have a licensing deal with Dow Chemical, and Dow is currently building a factory in South Korea to ramp up production of quantum-dot film. Nanoco’s cadmium-free technology will be found in LG’s quantum-dot TVs in 2015.
Nanosys is another film-based producer that has partnered with 3M on the film-sheet technology. It makes both cadmium-based and cadmium-free quantum dots. They are the company behind Amazon’s HDX 7 display and the Asus Zenbook NX500. Samsung licenses the cadmium-free quantum-dot tech in its new SUHD 4K sets from Nanosys. Nanosys is also working with Panasonic, Hisense, TCL, Changhong, and Skyworth.