Quantum dot-based displays offer improved power economy, brightness, and color purity over earlier display generations. A revolutionary approach based on self-organizing chemical structures provides a remedy. The production and analysis of these innovative blue quantum dots required a state-of-the-art imaging methodology.

Although QD-LED displays are now available, the technology is still in its early stages, and the available models have several shortcomings, particularly their blue subpixels. The most significant blue subpixels are those of the three primary colors. Down-conversion is the process by which blue light is converted into green and red light. Blue quantum dots hence need more precisely regulated physical characteristics. This frequently means that producing blue quantum dots is extremely difficult and expensive and that the quality of these dots is crucial to any display.

But now, a group of scientists under the direction of Professor Eiichi Nakamura from the Department of Chemistry at the University of Tokyo has a solution.

Professor Eiichi Nakamura from the University of Tokyo’s Department of Chemistry said, “Previous design strategies for blue quantum dots were very top down, taking relatively large chemical substances and putting them through a series of processes to refine them into something that worked. Our strategy is bottom-up. We built on our team’s knowledge of self-organizing chemistry to control molecules precisely until they form the structures we want. Think of it like building a house from bricks rather than carving one from stone. It’s much easier to be precise, design the way you want, and more efficient and cost-effective.”

But the blue quantum dot created by Nakamura’s team is unusual not simply because of how it was made; when exposed to ultraviolet radiation, it emits almost perfect blue light, in accordance with the BT.2020 international standard for assessing color accuracy. This is because their dot has a special chemical composition that combines both organic and inorganic substances, such as lead perovskite, malic acid, and oleylamine. And they can only be forced into the necessary shape, a cube of 64 lead atoms, four to a side, through self-organization.

cinematic chemistry
The second challenge. Stills from the video captured using “cinematic chemistry” of the blue quantum dot, including an illustration showing the atomic arrangement of the sample. ©2022 Nakamura et al.

Nakamura said, “Surprisingly, one of our biggest challenges was finding that malic acid was a key piece of our chemical puzzle. It took over a year of methodically trying different things to find it. Perhaps less surprising is that our other main challenge was to determine the structure of our blue quantum dot. At 2.4 nanometers, 190 times smaller than the wavelength of the blue light we sought to create with it, the structure of a quantum dot cannot be imaged by conventional means. So, we turned to an imaging tool pioneered by some of our team known as SMART-EM, or ‘cinematic chemistry’ as we like to call it.”

As the blue quantum dot is also quite short-lived, though this was expected, and the team is now aiming to improve its stability with the aid of industrial collaboration.

Journal Reference:

  1. Olivier J. G. L. Chevalier, Takayuki Nakamuro, Wataru Sato, Satoru Miyashita, Takayuki Chiba, Junji Kido, Rui Shang, Eiichi Nakamura, “Precision synthesis and atomistic analysis of deep blue cubic quantum dots made via self-organization,” Journal of the American Chemical Society: November 8, 2022, DOI: 10.1021/jacs.2c08227.