Introduction of Quantum Dots
Quantum dots (QDs) are a class of nanomaterials that have size-tunable optical and electronic properties. In 2023, the Nobel Prize in Chemistry was awarded to three scientists Mounqi Bawendi, Louis Brus and Alexei Ekimov for their groundbreaking work on the discovery and synthesis of QDs. The discovery of QDs not only drives the development of nanotechnology, but also revolutionizes various fields such as display technology, medical imaging, solar cells and quantum computing.
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Discovery of Quantum Dots
1. Preliminary exploration and theoretical basis
The discovery of QDs can be traced back to the study of nanoscale materials. In the 1980s, the scientific community began to pay attention to the quantum effects of nanomaterials. In 1981, Alexei Ekimov observed for the first time size-tunable quantum effects in glass matrices at the Vavilov Institute of Optics in the Soviet Union, and discovered that the color of CuCl-doped glass would change with the size of the particles. This discovery laid the theoretical foundation for QDs.
In 1983, Louis Brus independently synthesized size-tunable CdS nanocrystals at Bell Labs and observed quantum effects in liquid suspension. Although the research results of the two scientists had not been shared with each other at that time, they had not yet been officially linked through academic or other channels until 1984.
2. Naming and definition of quantum dots
In 1983, for the first time, Brus' team proposed the term "quantum dot" to describe the properties of these nanocrystals. The definition of quantum dots is: semiconductor nanocrystals, usually between 1-20 nanometers in size, which exhibit size-dependent quantum effects.
3. Synthesis and perfection of quantum dots
In 1981, the quantum size effect was first discovered by Alexei Ekimov. By inducing size-dependent quantum effects in glass, he successfully controlled the size of CuCl particles and changed the color of the glass. Later in 1983, Louis Brus further developed this technology and for the first time synthesized similar crystals in liquid solutions, providing more controllability and finer crystal studies.
In 1993, under the guidance of Brus, Mounqi Bawendi developed a new colloidal synthesis method. Using high-boiling-point, non-polar organic solvents and the "hot injection" technology, the nucleation and growth kinetics of nanocrystals were successfully controlled to prepare quantum dots with high crystallinity and uniform size. This method laid the foundation for the wide application of quantum dots.
Three Scientists' Contributions to Quantum Dots
Louis Brus: The first experimental verification of the quantum size effect
Louis Brus is an American physical chemist. He was born in Cleveland, Ohio, USA in 1943. In his early years, he received a bachelor's degree in chemical physics from Rice University in Houston and a doctorate in 1969. In 1973, he joined AT&T Bell Laboratories and later moved to Columbia University in 1996. Brus' research initially focused on the exploration of colloidal semiconductors, and in 1983, he first synthesized size-tunable CdS nanocrystals and observed quantum effects in suspension. He found through experiments that the smaller the size of the nanocrystal, the shorter the wavelength of light it absorbs and emits (blue shift), while larger nanocrystals absorb longer wavelengths of light (red shift). This phenomenon is called the "Quantum Size Effect" and is one of the core theories of QD research.
In addition, Brus also collaborated with Moungi Bawendi in the late 1980s to develop the "Hot-Injection Method", which realized the synthesis of highly monodisperse QDs by controlling temperature and solvent conditions. This method laid the foundation for the subsequent commercial application of quantum dots, such as QLED displays, LED lights, etc. In addition, after joining Columbia University in 1996, Brus continued to promote the application of quantum dots in biomedical imaging and optoelectronic devices.
Moungi Bawendi: Synthesis of high-quality quantum dots
Moungi Bawendi is a French-American chemist, who was born in Paris, France in 1961. In 1988, he joined the team of Louis Brus as a postdoctoral researcher. In 1993, Bawendi developed a revolutionary synthesis method that realized high monodispersity and high-quality quantum dot synthesis through the hot injection reaction of organometallic precursors. This method is called "Hot-Injection Synthesis", and its core lies in the controllable growth of nanocrystals by precisely controlling temperature, solvent and precursor concentration. Bawendi's method not only improves the optical properties of quantum dots, but also makes them more stable and reproducible in industrial applications.
Bawendi's work has paved the way for the wide application of quantum dots. For example, quantum dots are now widely used in QLED TV screens, color enhancement of LED lights, and biomedical imaging and diagnosis. His research has also promoted the application of quantum dots in flexible electronics, microsensors, and solar cells. In 2023, Bawendi won the Nobel Prize in Chemistry along with Brus and Ekimov for their contributions to the synthesis of quantum dots.
Alexei Ekimov: Quantum effects in glass matrices
Alexei Ekimov is a Russian-American physicist who was working at the Vavilov Institute of Optics in the Soviet Union in 1981. He was the first person to observe the size-dependent quantum effect in glass matrices. In 1981, Ekimov observed while studying the doped glass that the nanoparticles formed in the glass during the doping process also have an impact on the optical properties of glass. For example, doping CuCl into the glass will change its color due to the size of the particles in it. This laid the foundation for the subsequent discovery of quantum dots. Ekimov's research showed that quantum effects can also exist in non-free suspension systems, further broadening the research scope of quantum dots.
In addition to promoting the application of quantum dots in optical materials, Ekimov's research also provided a theoretical basis for the subsequent synthesis and characterization of quantum dots. For example, the "Ekimov model" put forward by him provided a very important reference for the subsequent research on size control and optical properties of quantum dots. In 2023, together with Brus and Bawendi, Ekimov won the Nobel Prize in Chemistry.
Application and Development of Quantum Dots
Application of quantum dots in display technology
The application of quantum dots in display technology is one of the most extensive and mature fields. Quantum dots are widely used in QLED (quantum dot light-emitting diode) display technology due to their high quantum efficiency, narrow emission peak, high color saturation and good stability. Compared with traditional LCD (liquid crystal display), QLED has more accurate color performance and higher brightness, which can significantly improve the visual effect of the display. In addition, quantum dots can also be combined with new display technologies such as OLED and Micro-LED to further improve the performance and manufacturing efficiency of the display. At present, QLED technology has been widely used in high-end TVs, computer monitors and smartphone screens.
Application of quantum dots in the biomedical field
The application of quantum dots in the biomedical field is also quite remarkable. Due to its high brightness, narrow emission peak and good biocompatibility, quantum dots are widely used in biomarkers, cell imaging, disease detection and drug delivery. For example, quantum dots can be used as fluorescent probes to combine with specific biomolecules to emit light of a specific color, thereby achieving real-time tracking of cells and tissues. In addition, quantum dots can also be used for the early screening and treatment of tumors, helping doctors perform surgery more accurately by marking tumor cells. Compared with traditional organic dyes, quantum dots have higher brightness and longer photostability, and can provide clearer imaging effects.
Application of quantum dots in optoelectronic devices and energy
Quantum dots not only perform well in the fields of display and biomedicine, but also show great potential in optoelectronic devices and energy. In the field of optoelectronic devices, quantum dots can be used to manufacture efficient light-emitting diodes (LEDs), photodetectors, and lasers. For example, quantum dots can be used as the active layer of solar cells to improve the efficiency of solar cells by absorbing light energy and converting it into electrical energy. In addition, quantum dots can also be used in photocatalytic reactions. Efficient photocatalytic systems can be designed by combining their unique energy level structure and redox potential. In the future, quantum dots are expected to play an important role in flexible electronic devices, microsensors, thinner solar cells, and encrypted quantum communications.
