Once thought impossible to manufacture, quantum dots have become a common component in computer monitors, TV screens, and LED lamps, among other uses. Three of the scientists who pioneered these unique nanocrystals—Moungi G. Bawendi, Louis E. Brus, and Alexei I. Ekimov—that has been given to him Nobel Prize 2023 in Chemistry by the Royal Swedish Academy of Sciences “for the discovery and synthesis of quantum dots.” The news had already appeared in the Swedish news media — a rare event — when Johan Aqvist, chairman of the Nobel Academy’s committee for chemistry, made the official announcement, complete with five flashes containing quantum dots of various colors. it is in front of you like a sight. help
A quantum dot is a tiny semiconducting bead with a few tens of atoms in diameter. Billions can fit into a pin, and the smaller you can make them, the better. At those low frequencies, quantum effects kick in and give higher energy signals and optical properties. They glow when lit, and the color of the light is determined by the size of the quantum dots. Larger dots emit red light; small dots emit blue light. Therefore, you can adapt quantum dots to specific wavelengths by changing their size.
Scientists have thought since the 1930s that particles at the nanoscale would behave differently. That’s because, according to quantum mechanics, there is much less space for electrons when the particles are smaller, electrons squeeze so tightly that the material’s properties can change dramatically. Scientists succeeded in making nanoscale-thin films on top of bulk materials in the 1970s that have size-dependent optical properties, consistent with previous predictions. But making those films requires high-vacuum conditions and temperatures near absolute zero, so no one expects them to have much practical use.
A solution emerged from the study of ancient colored glass. Glass makers long ago discovered that they could add silver, gold, or cadmium to their molten glass, vary the temperature, and control the cooling process to produce different shades of colored glass. Later, scientists found that the color comes from the small particles in the glass, and the color depends on the size of those particles.
In the late 1970s, Ekimov, as a newly minted PhD, began researching the optical properties of colored glass at the SI Vavilov State Optical Institute in what was then the Soviet Union. He drew on some of the optical research methods he plans to use for his doctoral research on semiconductors, shining light on materials and measurements as he gets to learn more about crystal structure.
Ekimov began tinting his lab-made glass with copper chloride, X-raying the resulting glass after cooling. He found that small crystals of copper chloride were formed and how they were formed — varying the temperature between 500 ° – 700 ° C and heating times from one hour to 96 hours — affected the measurements, which range from about 2 nm to 30 nm. Also, a particle size affects the light absorption of glass, just like the thin films created in the 1970s: the smaller the particles, the more blue light they absorb. These were the first quantum dots deliberately made in the laboratory.
Alas, Ekimov’s 1981 paper announcing its discovery was published in a Soviet newspaper, so researchers elsewhere in the world had no access. That included Brus, who published a 1983 paper announcing his discovery of free-floating nanoparticles in a solution that also exhibited size-dependent optical effects.