![]() The researchers were able to show that the caesium lead halide quantum dots differ from other quantum dots: their most likely excited energy state is not a dark state. This limits the brightness," says Rainer Mahrt, a scientist at IBM Research. "In such a dark state, the electron hole pair cannot revert to its energy ground state immediately and therefore the light emission is suppressed and occurs delayed. Under certain conditions, different excited energy states are possible in many materials, the most likely of these states is called a dark one. If the electron-hole pair reverts to its energy ground state, light is emitted. The result is an electron-hole pair in an excited energy state. "You can use a photon to excite semiconductor nanocrystals so that an electron leaves its original place in the crystal lattice, leaving behind a hole," explains David Norris, Professor of Materials Engineering at ETH Zurich. Understanding why caesium lead halide quantum dots are not only fast but also very bright entails diving into the world of individual atoms, light particles (photons) and electrons. He is a doctoral student at ETH Zurich and is carrying out his doctoral project at IBM Research.Įlectron-hole pair in an excited energy state "However, caesium lead halide quantum dots emit light at room temperature after just one nanosecond," explains Michael Becker, first author of the study. Previously-studied quantum dots typically emit light around 20 nanoseconds after being excited when at room temperature, which is already very quick. The scientists were able to confirm that the nanocrystals emit light extremely quickly. In a study published in the most recent edition of the scientific journal Nature, the international research team examined these nanocrystals individually and in great detail. These quantum dots are thus also being treated as components for future light-emitting diodes and displays. By varying the composition of the chemical elements and the size of the nanoparticles, he also succeeded in producing a variety of nanocrystals that light up in the colours of the whole visible spectrum. "These tiny crystals have proved to be extremely bright and fast emitting light sources, brighter and faster than any other type of quantum dot studied so far," says Kovalenko. Three years ago, Maksym Kovalenko, a professor at ETH Zurich and Empa, succeeded in creating nanocrystals - or quantum dots, as they are also known - from this semiconductor material. ![]()
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