Quantum dots in your TV!

This years CES (consumer electronics show) has just drawn to a close. A place where us tech obsessed nerds scour the exhibitor list looking for the next big thing in gadgets and gismos. Drones and wearable devices were prominent this year, but the big announcement that caught my nano attention was the launch of Quantum Dot televisions.

Claiming to be brighter, more colourful and more efficient, several of the large companies including Samsung and LG launched their quantum dot TV range at CES, but what are these quantum dots and how do they help your television?

Quantum Dots

Quantum dots (also known as nanocrystal semiconductors) are nanoparticles which glow when you shine light on them and they usually range from 2-10 nanometers or 10-50 atoms in diameter.

Quantum effects arise from the confinement of electrons and “holes” in the material (a hole is the absence of an electron and these holes cause the dot to behave as though it were a positively charged particle). The dots are excited by an energy source such as light and the smaller the dot, the higher the energy and intensity of its emitted light. The colour of the light that the dot emits will depends on the size and chemistry of the dot itself. Larger dots emit a redder light and shift towards a shorter wavelength blue colour as the dot gets smaller. A whole rainbow of colours can be emitted from a single material just by changing the quantum dot size.

Quantum Dot Backlit LCD TV’s

Quantum dot enhanced television (left) compared to standard LCD television (right) (Image Source Nanosys)

Quantum dot enhanced television (left) compared to standard LCD television (right) (Image Source Nanosys)

The TV technology just uses a standard LED backlit LCD (liquid crystal display) television with the slight modification of the light source colour and the addition of a quantum dot film layer.

Current LCD TV’s makes pictures by using thousands of pixels made up of red, green and blue subpixels. These colours are displayed by filtering the white light that is produced from the LED backlight, which oddly enough isn’t usually from a white LED, but from a blue one covered with yellow phosphor to produce white light.

This white light must be filtered well to prevent shades of pink and yellows coming through which results in a modified final red, green and blue tone. The better these filters are at removing the other colours, the less original light gets through which results in picture with lower brightness and a less efficient TV.

Step in the Quantum dot!

As quantum dots absorb light of one wavelength and convert it to light of another wavelength, the size of the dots are tailored specifically for the red and green colours needed by television pixels.

Instead of using a white LED backlight, the Quantum dot television uses a blue LED instead which it passes through a film filled with red and green light generating quantum dots. When you look at the blue LED light shining through the red and green quantum dots, the combined emitted light looks pure white without needing to be filtered, resulting in a minimal about of light lost.  This results in an incredibly bright output and much more efficient light use.

Schematic showing comparison of quantum dot enhanced LCD TV (left) compared to standard LCD TV (right)

Schematic showing comparison of quantum dot enhanced LCD TV (left) compared to standard LCD TV (right)

Because the LCD screen now has a much better source of light to work with and can efficiently convert red and green more precisely, the final result is what the TV nerds call a wider colour gamut (where a gamut is the range of colours a device can reproduce).

Quantum dot televisions are still in their infancy, primarily due to the limitations in producing large quantities of dots as well as the small number of suppliers that can produce cadmium free dots (a requirement by several countries due to the toxicity of cadmium).  However, as the technology improves and the demand for more efficient, better quality screens increases, I think we will be hearing a lot more about quantum dots in our devices over the next few years.



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