Using Quantum Dots in Displays

Contemporary scientists and engineers have been making significant progress in the application of quantum discoveries and nanotechnologies to areas comprising computing, cryptology, imaging, metrology and sensing.

For anyone spending any amount of time around the display industry in recent years, they have likely heard about a concept known as quantum dots and novel "QLED" technologies being utilized to generate displays with brighter, more colorful and more realistic visual images.

Quantum Dots

In essence, quantum dots are minute semiconductors, each measuring just a single nanoparticle (nanocrystal) between 2 and 10 nanometers (nm) in diameter. As a result of their small dimensions, these nanoparticles embody special optical and electrical characteristics—for instance, during exposure to light they can emit pure, monochromatic light (red, blue, and green), wherein the color of the light is dependent on the size of the nanoparticle. Quantum dots embody a varied range of applications beyond displays and can be utilized for fluorescence, photonics, and electrochemical applications.

The color of a quantum dot depends on the size of the particle; different sizes produce different wavelengths. Photo source: Nanosys

The color of a quantum dot depends on the size of the particle; different sizes produce different wavelengths. Photo Source: Nanosys

There are two categories of dots: photo-emissive and electro-emissive (electroluminescent). Photo-emissive quantum dots can be utilized in a display layer, converting monochromatic blue light from an LED backlight to emit pure colors for LCD screens. Electro-emissive quantum dots can be utilized as light-emitting diodes, much like active-matrix organic light-emitting diode (AMOLED) or microLED displays, but televisions utilizing electro-emissive particles remain experimental.

Vials containing quantum dots: fluorescent nanoparticles of semiconducting material. Image credit: PlasmaChem

Vials containing quantum dots: fluorescent nanoparticles of semiconducting material. Image Credits: PlasmaChem

Quantum Display Applications

From the early 2000s, scientists and display industry innovators have been researching quantum dot technology due to their potential for generating a larger producible color gamut with ultra-deep colors. Following the introduction of wide-color gamut and HDR televisions, demand for displays capable of a larger quantity of saturated colors has multiplied. Due to their capacity for generating spectrally pure wavelengths of light, quantum dots can reach almost 100% of the Rec. 2020 (BT2020) color gamut, in addition to 100% DCI-P3 coverage.

Quantum dots are also characterized by extreme energy efficiency, meaning a display (particularly a large display such as a television screen) utilizing quantum dot technology can generate brighter whites using less energy. Commercially available quantum displays are all part of the “QLED” category, pioneered by Samsung, who introduced the first QLED TVs at CES in 2017.

QLED displays utilize the aforementioned photo-emissive category of the quantum dot. Among such displays, a photo-emissive quantum-dot layer operates as a filter for refining the color temperature and enhancing brightness of light generated by the backlight. Rather than the white backlight utilized in conventional LED displays, quantum dot panels utilize an energy-efficient blue LED backlight. Because the LED emits blue light, blank pixels are used to permit the blue light to pass through.

Red and green quantum dots exist on the top filter layer and utilize the energy of the backlight to produce red and green hues in the display. This enables particularly accurate color tuning (based on the size of the dots) to generate the broader color gamut.

Samsung’s 2019 65” QLED 4K Ultra-HD television.

Samsung’s 2019 65” QLED 4K Ultra-HD television.

It is critical to point out that quantum dots in QLED displays do not independently produce light, in spite of the assumption regarding a display prefixed with "light-emitting" (rather, the "LED" in QLED corresponds to the LED backlight). In several respects, the performance of QLED can be favorably compared to the most recent emissive display technology, OLED (organic light-emitting diodes).

If emissive quantum dots (of the electro-emissive category), can substitute the quantum filter (of the photo-emissive category), display performance and energy efficiency of quantum-dot displays might be enhanced. Referred to as direct-view quantum dot displays, such screens of the future might generate the ultimate black levels, brightness, color gamut and contrast ratios with unprecedented energy efficiency.

Quantum Display Quality and Performance

Although they might yield superior performance, quantum-dot displays remain subject to identical quality issues as conventional displays. Dead pixels, mura (blemishes), and non-uniformity can undermine the viewing experience if not detected and corrected during production. Radiant’s ProMetric® Imaging Photometers and Colorimeters quantify display performance and uniformity down to the pixel and sub-pixel level, which matches the acuity and discernment of human visual perception. For instance, Radiant has conceived of a proprietary methodology for the measurement and correction of pixel-to-pixel variation in OLED, microLED, and similar categories of emissive displays.

Mura identified on a display using Radiant’s TrueTest™ Software.

Mura identified on a display using Radiant’s TrueTest™ Software.

Radiant’s FPD conoscope lens allows high-resolution photopic quantification of the angular distribution of color, luminance, and contrast in flat panel displays and display components, including those based on LCD and OLED technologies, in addition to backlights. All of Radiant’s display measurement solutions offer fast, precise results, rendering each system optimal for R&D projects and automated in-line production quality control.

Acknowledgments

Produced from materials originally authored by Anne Corning from Radiant Vision Systems.

This information has been sourced, reviewed and adapted from materials provided by Radiant Vision Systems.

For more information on this source, please visit Radiant Vision Systems.

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