Nobel Prize in Chemistry for quantum dots

The 2023 Nobel Prize in Chemistry has been awarded to Moungi G. Bawendi of Massachusetts Institute of Technology, Louis E. Brus of Columbia University, and Alexei I. Ekimov of Nano crystals Technology Inc. in New York for the discovery and development of quantum dots. The 2023 Nobel Prize for chemistry isn’t the first Nobel awarded for research in nanotechnology. However, this year’s trio of Nobel laureates was part of the earliest wave of modern nanotechnology where researchers began use. But it is perhaps the most colorful application of the technology to be associated with the accolade. The three scientists each contributed to a “fundamental discovery in nanotechnology,” according to officials from the Royal Swedish Academy of Sciences, which awards several of the prizes each year. The work they’ve done has already led to new technology in television screens and in bio imaging. Dr. Bawendi, born in 1961 in France, is a professor at the Massachusetts Institute of Technology and used to study under Dr. Brus as a postdoctoral researcher. Dr. Brus, born in 1943 in Cleveland, is a professor emeritus at Columbia University. Dr. Ekimov, born in 1945 in the former Soviet Union, was previously the chief scientist at Nano crystals Technology, a company based in New York.
Quantum dots are particles that are so incredibly small that their size actually starts to affect their properties. For example, blue quantum dots and red quantum dots can be made from the exact same material, with the only difference being the size of the particle itself. (The blue quantum dots are smaller than red ones.)In fact, changing the size can alter many different properties beyond just color – which means that quantum dots could be useful for a variety of applications, including building better solar panels and perhaps even creating fuel by using sunlight (something that plants do to generate sugars).While it may sound like a subject closer to physics, officials said that it was chemists who did much of the fundamental research in this field. The three scientists will share the prize money of 11 million Swedish kronor (close to $995,000) in equal parts.
Quantum dots brilliantly fluoresce: They absorb one color of light and re-emit it nearly instantaneously as another color. A vial of quantum dots, when illuminated with broad spectrum light, shines with a single vivid color. What makes them special, though, is that their color is determined by how large or small they are. Make them small and you get an intense blue. Make them larger, though still Nano scale, and the color shifts to red. This property has led to many arresting images of rows of vials containing quantum dots of different sizes going from a striking blue on one end, through greens and oranges, to a vibrant red at the other. So eye-catching is this demonstration of the power of nanotechnology that, in the early 2000s, quantum dots became iconic of the strangeness and novelty of nanotechnology. But, of course, quantum dots are more than a visually attractive parlor trick. The wavelengths of light that a material absorbs, reflects or emits are usually determined by the chemical bonds that bind its constituent atoms together. Quantum dots work differently. Rather than depending on chemical bonds to determine the wavelengths of light they absorb and emit, they rely on very small clusters of semiconducting materials. It’s the  quantum physics of these cluster that then determines what wavelengths of light are emitted—and this in turn depends on how large or small the clusters are. This ability to tune how a material behaves by simply changing its size is a game changer when it comes to the intensity and quality of light that quantum dots can produce, as well as their resistance to bleaching or fading, their novel uses .
Semiconductors are crystals that help power our electronics. But while traditional crystals may be quite large at the molecular level, a quantum dot consists of just a few thousand atoms squished into a space just a few nanometers across. The difference in size between a quantum dot and a soccer ball is about the same as the difference between a soccer ball and the Earth, the Nobel Foundation said. “For a long time, nobody thought you could ever actually make such small particles,” Johan Aqvist, the chair of the Academy’s Nobel committee for chemistry, said at the news conference announcing the 2023 laureates. Presenting the topic with five colorful flasks lined up in front of him, which he said contained quantum dots in a liquid solution, he said, “But this year’s laureates succeeded.”
Electrons exist at fixed distances from an atom’s nucleus; with higher energy levels corresponding to greater distances. When atoms get energized, their electrons temporarily jump to greater distances and higher levels. When they fall back down, the electrons release the extra energy as light. A basic principle of quantum mechanics is that objects can behave like particles or like waves. The same holds true for electrons: Like other types of waves, they have a frequency that relates to the color of light they release. Scientists have known since the 1930s that squeezing atoms into a tiny enough “container” could increase the frequency of their electrons and change the type of light the material absorbs or emits. That container is a crystal, called a quantum dot because it triggers the wavelike behavior theorized by quantum mechanics. But that thought stayed theoretical, because scientists didn’t know how to squeeze a material to the point where such quantum effects would take over. In the 1970s, Dr. Ekimov began studying how colored glass could differ in hue depending on how long it was heated. He found that when heated, copper chloride crystals formed inside the glass. The smaller the crystals, the bluer the glass appeared. Independently, Dr. Brus discovered the same effect using cadmium sulfide crystals. These were the first observations of a quantum effect that depended on size, rather than the elemental makeup of the material. Still, scientists had to figure out how to control this effect to harness it for real-world applications.
Of course, few materials are completely nontoxic, and quantum dots are no exception. Early quantum dots were often based on cadmium selenide for instance—the component materials of which are toxic. However, the potential toxicity of quantum dots needs to be balanced by the likelihood of release and exposure and how they compare with alternatives. Since its earlier days, quantum dot technology has evolved in safety and usefulness and has found its way into an increasing number of products, from display and lightning, to sensors, biomedical applications and more. In the process, some of their novelty has perhaps worn off. It can be hard to remember just how much of a quantum leap the technology is that’s being used to promote the latest generation of flashy TVs, for instance. And yet, quantum dots are a pivotal part of a technology transition that’s revolutionizing how people work with atoms and molecules.
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