Laser technology opens up a new way to synthesize quantum dots

Recently, professor duhiwen’s team developed a new process for synthesizing monodisperse quantum dots, which is environmentally friendly and efficient. The results were published in Nature Communications, which is the world’s first report on synthesizing monodisperse quantum dots by physical method.
Quantum dots, also known as semiconductor nanocrystals, are nanoparticles made up of ii-vi or iii-v elements. Quantum dot size, generally between 1 ~ 10 nm, due to the electrons and holes is strongly restricted in small volume, the quantum dot with the quantum confinement effect, show many unique physical properties, such as quantum dot light wavelength change with size adjustable, quantum dot is a photon radiation and can generate multiple free electrons, the photoelectric conversion efficiency compared with the material of the semiconductor be doubled, and so on. Based on these unique advantages, quantum dots have broad application prospects in solar cells, light-emitting devices, biomarkers and other fields. Quantum dots with a size difference of less than 10% are called monodisperse quantum dots. Such monodisperse quantum dots with uniform particle size have great application potential in nano-electronic devices due to their good machinability and performance consistency.
Traditionally, the preparation of quantum dots is mostly made by colloidal chemistry, which is a “bottom-up” method that USES a variety of precursors to combine and react at high temperatures to obtain the target molecule, and then thousands of target molecules pile up and grow into a single quantum dot. This method not only requires complex precursors, but also takes a long time to synthesize, from a few hours to a few days. In addition, in order to obtain uniform monodisperse quantum dots, surfactants are usually used, which will affect the next step of use and need to be removed through complicated procedures. Therefore, the method of colloidal chemistry can produce a large number of pollutants and impose a heavy burden on the environment.
After years of exploration, the research group of quantum dot materials and devices has developed a unique way to propose a “top-down” monodisperse quantum dot synthesis process, which USES a “mild” long pulse width infrared laser to irradiate the suspension of a large particle semiconductor to transform the non-uniform large particle into a small monodisperse quantum dot. The key to this process is the clever use of the quantum confinement effect of quantum dots: large semiconductor particles with narrow band gaps can absorb long pulse width infrared lasers, be heated and vaporized, and re-condense into very small quantum dots. Once quantum dots are made, their optical bandgap widens due to a quantum confinement effect, making them transparent to the infrared laser and thus protected from damage by laser heating. Under this effect, the semiconductor with large particles is continuously destroyed by heating, while the small quantum dots with uniform particle size are constantly formed, and only the monodisperse quantum dots are left in the solution. Because the process is essentially a physical crushing process, with a wide range of materials and even directly mined ore, it is environmentally friendly and produces almost no contaminants. However, the laser method is convenient and fast, and it only takes a few minutes to obtain high-quality monodisperse quantum dots.
In the future, the clean technology is expected to help make quantum dots more affordable, allowing them to play a more prominent role in disease diagnosis, water pollution detection, photoelectric conversion and other fields.

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