One of the most interesting meetings I had at CES this year was an update from Nanosys on the future of quantum dots in video displays. As you may know, quantum dots (QDs) are microscopic nanoparticles made of semiconductor material that emit light in a very narrow band of wavelengths when bombarded with light at a higher energy (shorter wavelength) than the emitted light. The wavelength of the emitted light is determined by the size of the QD.

In many current LCD TVs, quantum dots are used in the backlight system. Light from blue LEDs hits a polymer film embedded with two sizes of QDs that absorb some of the blue light and emit red or green light; when the red and green light from the QDs combines with the unabsorbed blue light from the LEDs, the result is white light, which then proceeds through the LCD layer and subpixel color filters to form the final image.

In a conventional QD backlight, blue light from LEDs stimulates the quantum dots in a film to emit red and green light, forming white light when combined with unabsorbed blue light. The white light then passes through red, green, and blue color filters.

Using QDs in the backlight of LCD TVs allows a wider color gamut than white LEDs can manage, and the spectrum exhibits less overlap between the peaks of red, green, and blue. However, the wavelengths of the QDs and the blue LED must match the color filters very closely to avoid a significant drop in light output.

At CES, Nanosys—which supplies or licenses QD technology to most of the major TV manufacturers—demonstrated the next step in the application of QDs to displays. Instead of a random distribution of red and green QDs in a polymer film, the quantum dots are incorporated into a photolithographic process that allows them to be segregated into patterns—specifically, the same pattern as the subpixel color filters found in LCD and WOLED TVs, as seen in the graphic at the top of this article.

The point is to replace the red and green color filters with tiny QD cells; the blue filters would be replaced by transparent cells that allow light from the blue LED backlight to pass through unimpeded. This would avoid any interference between the QDs and color filters, greatly increasing the efficiency of each color. And patterned photolithography is a mature process that can be performed in air at room temperature, making it relatively easy to implement.

In the photo-emissive color-conversion process, the red and green subpixel color filters are replaced by patterned QDs; the blue color filters are replaced by a transparent cell that simply passes light from the blue LED backlight.

In addition to LCD TVs, this so-called photo-emissive color-conversion approach can also be applied to WOLED TVs. LG's OLED panels—which are used in other companies' OLED TVs as well—use white OLED material and color filters, just like LCD TVs. If the filters are replaced by QD cells, there would be no optical cavities and thus no off-axis color distortion. This might require the use of blue OLED material, which has a shorter lifespan than other colors, but I was told this is improving as development continues.

The incorporation of QDs in patterned photolithography will eventually lead to the next step—direct emission of red, green, and blue light by electrical stimulation with no need for a backlight at all. This has often been called "QLED," a term that Samsung introduced at CES for its new line of LCD TVs with a "conventional" QD-based backlight, which caused some confusion.

The ultimate QD display technology is called electro-emissive, in which the quantum dots are electrically stimulated to emit red, green, and blue light with no need for a backlight at all.

In reality, electro-emissive QD displays are a few years away from commercialization, but Nanosys claims that we could see displays with photo-emissive QDs instead of color filters next year.