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The amazing journey of quantum dots: Why are they called "artificial atoms"
In the field of nanotechnology and materials science, quantum dots (QDs) have recently become a hot topic. These semiconductor nanocrystals, which are only a few nanometers in size, have optical and electronic properties that are very different from those of larger particles. Quantum dots are so attractive in part because of the quantum mechanical effects they exhibit, which have led to these tiny particles being vividly referred to as "artificial atoms."
Quantum dots are thought to possess properties intermediate between those of bulk semiconductors and discrete atoms or molecules.
When the quantum dots are exposed to ultraviolet light, the electrons are excited to a higher energy state. In semiconductor quantum dots, this process corresponds to the transfer of electrons from the valence band to the conduction band. When the electron returns to the valence band, it releases light energy, and this light radiation is called photoluminescence. Interestingly, the color of the emitted light varies depending on the energy difference of the quantum dots, and this property makes quantum dots have important potential in applications.
The optical and electrical properties of quantum dots change as they change size and shape. Generally speaking, quantum dots with a diameter of 5-6 nanometers emit radiation with longer wavelengths, such as orange or red, while quantum dots with a diameter of 2-3 nanometers emit shorter wavelengths of light, including blue and green. . The exact colors these appear depend on the chemical composition of the quantum dots. These properties make quantum dots show potential application prospects in many high-tech fields, including single-electron transistors, solar cells, LEDs, lasers, single-photon sources, second harmonic generation, quantum computing, biological cell research, microscopy, and Medical imaging, etc.
The comprehensive application potential of quantum dots makes them an indispensable tool in many scientific researches.
Quantum dots can be prepared using a variety of techniques, including colloidal synthesis, self-assembly, and electrical external stimulation. Colloidal synthesis is one of the most common methods, which usually involves heating the solution to induce the decomposition of the starting materials, forming monomers and generating nanocrystals. Temperature and monomer concentration are key factors affecting crystal growth. During this process, the activated atoms rearrange and crystallize, affecting the properties of the final quantum dot.
In practical applications, quantum dots often require additional layers to enhance their performance. These additional layers can reduce the risk of nonradiative recombination and thus increase the light quantum yield. Among the various quantum dot heterostructures, type I structures include a semiconductor core wrapped in a second material, while type II structures enable spatial separation of charge carriers, thereby improving brightness.
A typical structure of quantum dots is the CdSe/ZnS system, a combination of core and shell materials that enables these nanocrystals to emit light efficiently.
Regarding the manufacture of quantum dots, in addition to colloidal synthesis, plasma synthesis has also become increasingly popular. This method is particularly suitable for the production of covalently bonded quantum dots. By using non-thermal plasma, scientists can control the shape, size and composition of quantum dots. The traditional production method is high-temperature double injection, which can support mass production, but maintaining stability and quality during the production process is a major challenge.
With the advancement of technology, many companies have begun to study heavy metal-free quantum dot materials, which not only meet environmental protection requirements, but also have performance close to traditional CdSe quantum dots. The development of quantum dot technology is transformative for many industries, such as display technology and biomedical imaging.
Health and environmental considerations make the development of heavy metal-free quantum dots a top priority, including the cooperation of microorganisms and the application of diverse materials.
In summary, quantum dots, as the shining "artificial atoms", promise to provide new possibilities for future technology. They not only improve our understanding of the microscopic world, but also promote the innovation of new technologies. Does this mean that quantum dots will become ubiquitous technology in the near future?
