Quantum dots: The ultimate down‐conversion material for LCD displays

Abstract

Assuming large color gamut and therefore better color reproducibility will be a highly desired feature of all displays as we look to the near future, we make the case in this paper that Quantum Dots (QDs) are currently the down-conversion technology of choice that will allow liquid crystal display (LCD) makers to cost-effectively reach and exceed 100% of the NTSC (National Television Standard Committee) standard while achieving maximum system efficiency. We will discuss in detail the numerous fundamental advantages of QDs over phosphors, along with their scientific origins, and make the case that QDs are the ultimate light generating material for next-generation displays. OBJECTIVE AND BACKGROUNDLCD backlights generate light that is transmitted through a color filter array (CFA) in the liquid crystal panel, which together determine the range of colors the display can render and therefore size of the color gamut. By changing the spectral profile of the backlight unit with down-conversion materials, wider color gamuts can be achieved than with the typical yellow phosphor (Ce:YAG) and blue LED system.Recently, several types of red and green emitting phosphors [1] have been re-formulated to have narrower band emission compared to yellow phosphors typically used for white LED LCDs, increasing the color gamut to ~80% coverage of NTSC (~60% coverage of Rec. 2020) at reasonable system efficiencies. While it is possible that narrow-band red and green emitting phosphor technology will continue to improve over the next several years and be applied more heavily to LCD displays, it is a mature technology that may be reaching practical limits. Colloidal semiconductor nanocrystals or quantum dots (QDs), on the other hand, represent a relatively new display technology that is demonstrating significant and fundamental advantages over sulfide and nitride based narrow-band red and green emitting phosphors. In this paper we will discuss recent progress on red and green emitting QD materials for display applications and compare and contrast fundamental emitter properties and future potential with those of red and green phosphors.The exceptional quality of QD materials and the degree of control over their important optical properties at mass production scales have allowed the launch of the first mainstream QD-enhanced consumer electronic products. Sony Bravia Triluminos TVs containing QD Vision's Color IQ TM optics were first announced at the 2013 Consumer Electronics Show with a color gamut of ~100% NTSC (CIE 1931) area. Recently 3M and Nanosys also successfully launched a main stream QD-enhanced display product with the Amazon Kindle Fire HDX 7.9" tablet. Figure 1 shows examples of these two QD-enhanced LCD displays. The benefits of using QDs as the down-conversion material for LCD displays are numerous, and many prominent analysts are now forecasting most wide color gamut LCD displays will be QD-enhanced over the next several years. Figure 2 shows the three primary architectures for incorporation of QDs into an LCD display,...

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