The Nobel Prize in Chemistry has been conferred to three American scientists for discovering and synthesizing quantum dots. The Royal Swedish Academy of Sciences awarded the Nobel Prize in Chemistry to Moungi G. Bawendi of Massachusetts Institute of Technology, Louis E. Brus of Columbia University, and Alexei I. Ekimov of Nanocrystal Technology Inc. on the 4th of October 2023.
The academy described the laureates’ work as having “planted an important seed for nanotechnology”. The prize winners created tiny particles which can emit light because of their small size. These particles are so small that they are measured in units called nanometres. To understand how small it is, a popular analogy is comparing the size of the quantum dot to a football as a football is to the size of the earth. Due to this extremely small size, they are governed by the rules of quantum effects, which dictates the physical properties of these quantum dots. Brus and Ekimov, independently from each other, created these quantum dots in the 1980s. About a decade later, Bawendi made significant upgrades to this technology and is credited for its current state and applications in the real world such as in QLED TVs and medical equipment for examining tissues.
Quantum dots had been theorized as early as the 1930s, when scientists predicted that particles in the nanoworld would have significantly distinctive characteristics from the macroworld. Using a mathematical approach and exploring the consequences of the Schrodinger equation, scientists estimated a variety of size-dependent quantum effects due to the electrons being huddled together. At the time, however, scientists did not have the required technology to create these nanoparticles.
Although not known at the time, the simplest technology to exercise the quantum effect had existed a few centuries back. Glassmakers would infuse different elements into the glass and heat them to create coloured glass. It was soon realized that the element would give different colours depending on how severely it was heated, and on the method used to cool it. Ekimov became intrigued by this and studied this effect in his postdoctoral research work. He realized that upon heating, crystals of the compound infused while making the glass had formed and the size of these crystals determined what light spectra they absorbed. Ekimov published his discovery in a Soviet journal, and in doing so became the first person to produce quantum dots. Due to the cold war period, scientists in the western world were unaware of this discovery. Brus subsequently became the first researcher in 1983 to discover size-dependent quantum effects in particles suspended in solution.
Although this was a revolutionary finding, there were still some practical challenges, such as the non-uniformity of crystals resulting in unpredictable characteristics and crystals containing defects. Bawendi worked to bridge these problems by injecting the crystalizing substance into the heated solvent until saturation point was reached. This resulted in the formation of tiny crystal embryos. Bawendi succeeded in creating nanocrystals of desired sizes by controlling thermal dynamics. This new and improved method of producing quantum dots has proved to be revolutionary for nanotechnology due to its ease of production, and almost perfect quantum effect.
Commercially, optically modifying quantum dots have been extensively used in QLED technology such as television and computer screens for their ability to convert blue light to light of various colours. In addition, doctors and biochemists attach quantum dots onto biological molecules to trace organs and cells. In the future, this technology may enable physicians to diagnose malignant and benign cancerous tumours.
Quantum dots open applications in several avenues such as communication, energy and sustainability, electronics, and robotics. The Nobel Laureates will be credited for their work with a medal and a $1 million cash reward in December.
Featured image credit: Niklas Elmehed
Featured image description: A sketch of the Nobel Laureates: Moungi Bawendi, Louis Brus, and Alexei Ekimov