Once thought to be impossible to manufacture, quantum dots have become common components in computer monitors, television screens, LED lamps, and more. His three scientists who pioneered these colorful nanocrystals: Moungi G. Bawendi, Louis E. Brus, and Alexei I. EkimovI received an award 2023 Nobel Prize in Chemistry by the Royal Swedish Academy of Sciences “for Discovery and synthesis of quantum dots. ” The news had already been circulating in the Swedish news media when Johan Akvist, the head of the Academy’s Nobel Committee for Chemistry, made the official announcement, with footage showing a large number of colored quantum dots in front of him. Five filled flasks were lined up. assistance.
Quantum dots are tiny semiconductor beads with a diameter of several dozen atoms. Billions of them can fit on the head of a pin, and the smaller the pin, the better. At such small scales, quantum effects come into play, giving the dots excellent electrical and optical properties. When exposed to light, they shine brightly, and the color of the light is determined by the size of the quantum dots. Larger dots emit more red light. Smaller dots emit bluer light. Therefore, quantum dots can be tuned to specific light frequencies simply by changing their size.
Since the 1930s, physicists have thought that nanoscale particles would behave differently. This is because, according to quantum mechanics, when particles are very small, there is much less space for electrons to exist, and the electrons are squeezed so tightly that material properties can change dramatically. . Consistent with early predictions, scientists successfully created nanoscale thin films with size-dependent optical properties on top of bulk materials in the 1970s. However, because the production of these films required ultra-high vacuum conditions and temperatures close to absolute zero, no one expected them to be put to practical use.
![Moungi Bawendi, Louis Brus, and Alexei Ekimov are pioneers in the development of quantum dots.](https://cdn.arstechnica.net/wp-content/uploads/2023/10/dots5-640x293.jpg)
Niklas Elmehed
Research into ancient colored glass has led to a solution. Glass makers long ago realized that by adding silver, gold or cadmium to molten glass, changing the temperature and controlling the cooling process, they could produce colored glass in different shades. Scientists later realized that the color came from tiny particles within the glass, and that the specific color depended on the size of those particles.
In the late 1970s, Ekimov, a newly minted Ph.D., began researching the optical properties of colored glasses at the SI Vavilov State Optical Institute in what was then the Soviet Union. He used some of the optical diagnostic methods he had used in his doctoral research on semiconductors, shining light on materials and measuring how they were absorbed to learn more about crystal structures.
Ekimov colored glass made in the laboratory with copper chloride and, after cooling, began to X-ray the resulting glass. He found that small crystals of copper chloride were formed, and that the method used to prepare them (varying temperatures between 500 and 700 degrees Celsius and varying heating times from 1 to 96 hours) produced crystals of about 2 nm to 30 nm. We found that it affected the size of the range. . Additionally, similar to the thin films created in the 1970s, particle size affected the light absorption of the glass. The smaller the particles, the more blue light they absorb. These were the first quantum dots intentionally created in a laboratory.
Sadly, the 1981 paper announcing Ekimov’s discovery was published in a Soviet journal and was therefore inaccessible to researchers elsewhere in the world. Among them was Bruce, whose 1983 paper announced the discovery of nanoparticles floating freely in solution that also exhibited size-dependent optical effects.