Alexei Ekimov maps the mysteries of coloured glass
The fact that a single substance could result in different coloured glass interested Alexei Ekimov, because it is actually illogical. If you paint a picture in cadmium red, it will always be cadmium red, unless you mix in other pigments. So how could a single substance give glass of different colours?
During his doctoral degree, Ekimov studied semiconductors – important components in microelectronics. In this field, optical methods are used as diagnostic tools for assessing the quality of semiconducting material. Researchers shine light on the material and measure the absorbance. This reveals what substances the material is made from and how well-ordered the crystal structure is.
Ekimov was familiar with these methods, so he began using them to examine coloured glass. After some initial experiments, he decided to systematically produce glass that was tinted with copper chloride. He heated the molten glass to a range of temperatures between 500°C and 700°C, varying the heating time from 1 hour to 96 hours. Once the glass had cooled and hardened, he X-rayed it. The scattered rays showed that tiny crystals of copper chloride had formed inside the glass and the manufacturing process affected the size of these particles. In some of the glass samples they were only about two nanometres, in others they were up to 30 nanometres.
Interestingly, it turned out that the glass’ light absorption was affected by the size of the particles. The biggest particles absorbed the light in the same way that copper chloride normally does, but the smaller the particles, the bluer the light that they absorbed. As a physicist, Ekimov was well acquainted with the laws of quantum mechanics and quickly realised that he had observed a size-dependent quantum effect (figure 3).
Illustration of quantum effects arise when particles shrink
Figure 3. Quantum effects arise when particles shrink. © Johan Jarnestad/The Royal Swedish Academy of Sciences
This was the first time someone had succeeded in deliberately producing quantum dots – nanoparticles that cause size-dependent quantum effects. In 1981, Ekimov published his discovery in a Soviet scientific journal, but this was difficult for researchers on the other side of the Iron Curtain to access. Therefore, this year’s next Nobel Prize Laureate in Chemistry – Louis Brus – was unaware of Alexei Ekimov’s discovery when, in 1983, he was the first researcher in the world to discover size-dependent quantum effects in particles floating freely in a solution.
https://www.nobelprize.org/prizes/chemi ... %20effects.
