Quantum dots belong to a new class of new materials - one of the solution nanocrystals. Solution nanocrystals have the dual nature of crystals and solutions, and quantum dots are materials in which breakthrough industrial applications are immediately available.
Unlike other nanocrystalline materials, quantum dots are based on semiconductor crystals. The size is between 1 and 100 nanometers, and each particle is a single crystal. The name of a quantum dot is derived from the quantum confinement effect of a semiconductor nanocrystal or a quantum size effect. When the semiconductor crystal is as small as nanometer scale (1 nanometer is approximately equal to one ten thousandth of the width of the hair strand), different sizes can emit light of different colors. For example, cadmium selenide, a semiconductor nanocrystal, emits blue light at 2 nm, red light when it reaches 8 nm, and green yellow orange in the middle. The chemical composition of the quantum dots, the luminescent color can cover the entire visible region from blue light to red light, and the color purity is high and continuously adjustable.
Quantum dots can be used in the biomedical field. We can use quantum dots to fully display the skeleton of the cell. Compared with other types of detection methods, quantum dot luminescent materials are certainly advantageous for detection. We can easily use multiple colors of quantum dots to simultaneously detect multiple pathogens or pesticide residues. Moreover, because the quantum dot absorption capacity is very large, the sensitivity can be greatly improved.
Quantum dots can also be used in the lighting industry. At present, the energy consumed by lighting is roughly equivalent to 20% of electrical energy. However, the light efficiency of artificial light sources is very low. For example, incandescent lamps with high illumination quality have a luminous efficacy of only 2%. If you can increase the efficiency to 20%, it means you can save 20% of energy consumption. The US Department of Energy's solid-state lighting roadmap has written a paragraph: quantum dots will play an important role in the field of human lighting.
In addition, there are display industries. The current first-generation quantum dot display device is a backlight product combining GaN LED and quantum dots. Both Najing and two high-tech companies in the United States have entered the commercialization stage. This new type of backlight makes display color purity and color saturation very high, which is difficult to match with other display technologies. As far as I know, a large domestic TV manufacturer will launch this new color TV at the end of this year or early next year.
From beginning to boom in the field of quantum dots <br> <br> originator, about in the late 1970s. At the time, chemists in Western countries were affected by the oil crisis and wanted to find a new generation of photocatalytic and photoelectric conversion systems that could use solar energy. Drawing on the principles of semiconductor solar cells, chemists began experimenting with the preparation of small semiconductor crystals in solution and studying their optoelectronic properties. Representative figures include BARD and BRUS in the United States, Ekimov in the former Soviet Union, and HENGLEIN in Germany.
In the lab, the researchers found a very strange phenomenon. For example, the large single crystal of lead sulfide is always familiar black, but the color of the nanocrystals that chemists make in solution is different, some are yellow, some are red, some are black, some are even without color. . What strange things happened?
Finally, the American scientist BRUS, the former Soviet Union's E-FROS gave a beautiful explanation, which is the "quantum confinement effect" theory. The publication time of their articles was somewhat different, but because of the isolation of the former Soviet Union, they did not know each other's work.
So far, chemists are playing a leading role in this field, and synthesizing quantum dots with performance requirements is still the most critical thing in the field. Prior to 1990, synthetic methods were based on traditional chemical methods for preparing colloidal small particles, such as coprecipitation, microemulsions, micelles, and the like. These methods are capable of controlling the size to a desired extent to some extent, but the optical performance is very poor and substantially does not emit light.
A very important thing happened between quantum dot research between 1990 and 1993. A new synthetic method called “metal organic-coordinating solvent-high temperature†was introduced. This method was first used in Bell Labs. Invented, it uses high toxicity and very unstable dimethyl cadmium as a cadmium source to synthesize high quality cadmium selenide at high temperature (about 300 degrees Celsius) and organic coordination solvent. This is a milestone for the entire field. However, this also leaves a challenge for the field. The raw materials they use are borrowed from “metal organic vapor depositionâ€. The dimethyl cadmium is explosive, even at room temperature, and it is very toxic and costly. These factors have led to the development of this field not being fast in the next 10 years, and only one material can be made.
Later, when I arrived at the University of Arkansas, we found a “green†organic solvent route that allowed the simple synthesis of quantum dots to enter laboratories around the world. As long as there is an ordinary chemical synthesis laboratory, it can be done in China. Next, we systematically explored the quantum dot growth mechanism, so that the range of relatively high quality quantum dots is gradually extended to other types of semiconductors. For these reasons, this “green†route is quickly being promoted around the world, including industry and academia.
I believe that scientific research falls into two categories, namely, "forward-looking exploration" and "systematic research." The above-mentioned work of Bell Labs in 1990 is a typical forward-looking exploration, and our laboratory's work in this century is closer to systematic research. The unknown world facing scientific research does not have the standard answer like an exam. Therefore, we can neither deny forward-looking exploration nor despise systematic research. At present, Chinese scientific research has a tendency to place too much emphasis on the former and pay too much attention to scientific hotspots.
Disruptive progress <br> <br> back to Zhejiang University, I slowly realize that quantum dot synthesis chemistry the real core issue is the excited state control. This is because, as a luminescent material, its performance can only be achieved in an excited state. For traditional synthetic chemistry, chemists only care about the ground state. Based on this new understanding, we have adopted some new synthetic control methods. As a result, we have some quantum dots that have never been seen before.
Based on these new quantum dots, we have seen the first subversive quantum dot application by working with the Associate Professor Jin Yizheng and the Najing Technology Company of the Zhejiang University Materials Department. That is the quantum dot LED (QLED) with excellent performance. After applying for a patent, we submitted the first article to Natue magazine. Already published online.
Light-emitting diodes (LEDs) are changing our lives, and energy-saving effects in lighting and display have been recognized, and this is the foundation of this year's Nobel Prize in Physics (GaN-Blue LED). Gallium nitride blue LEDs have been mass-produced, and related intellectual property rights have been firmly controlled by Japanese, American and European companies. However, the technology of GaN blue LED is based on epitaxial growth of a multilayer semiconductor single crystal on a sapphire single crystal substrate, requiring high vacuum equipment, ultra high purity raw materials, and high energy consumption in the preparation process. Therefore, its basic cost is large.
If quantum dot synthesis meets the requirements for LED optoelectronic performance, then quantum dot LEDs are expected to combine the advantages of both GaN LEDs and OLEDs. Our recent work confirms this vision. Nature's reviewers gave several indicators to allow us to make a horizontal comparison with OLED and other solution processing LEDs. The results show that although our QLEDs were prepared by solution method under relatively simple conditions, our devices almost completely outperformed.
LED is also the core component of the lighting industry. But compared with sunlight, the current white LED lamp is defective. It is artificial white light and has many high-energy photons. The impact of high-energy photons on human health has been shown to be unfavorable. In addition, the current white LED fever is more obvious, this is not good news. The white light of QLED can be completely consistent with the ideal illumination source, closer to natural light, and the heat is greatly reduced. The progress of our recent work shows that one day quantum dot LEDs will contribute to the lighting industry. The field of quantum dots has now evolved to a level that requires deeper, more systematic, and more integrated (or more intersecting) levels. Our QLED technology is currently in a leading position in the world and has established its own intellectual property rights. However, competition from MIT (QDVision), SAMSUMG, etc. is not to be underestimated.
Unlike other nanocrystalline materials, quantum dots are based on semiconductor crystals. The size is between 1 and 100 nanometers, and each particle is a single crystal. The name of a quantum dot is derived from the quantum confinement effect of a semiconductor nanocrystal or a quantum size effect. When the semiconductor crystal is as small as nanometer scale (1 nanometer is approximately equal to one ten thousandth of the width of the hair strand), different sizes can emit light of different colors. For example, cadmium selenide, a semiconductor nanocrystal, emits blue light at 2 nm, red light when it reaches 8 nm, and green yellow orange in the middle. The chemical composition of the quantum dots, the luminescent color can cover the entire visible region from blue light to red light, and the color purity is high and continuously adjustable.
Quantum dots can be used in the biomedical field. We can use quantum dots to fully display the skeleton of the cell. Compared with other types of detection methods, quantum dot luminescent materials are certainly advantageous for detection. We can easily use multiple colors of quantum dots to simultaneously detect multiple pathogens or pesticide residues. Moreover, because the quantum dot absorption capacity is very large, the sensitivity can be greatly improved.
Quantum dots can also be used in the lighting industry. At present, the energy consumed by lighting is roughly equivalent to 20% of electrical energy. However, the light efficiency of artificial light sources is very low. For example, incandescent lamps with high illumination quality have a luminous efficacy of only 2%. If you can increase the efficiency to 20%, it means you can save 20% of energy consumption. The US Department of Energy's solid-state lighting roadmap has written a paragraph: quantum dots will play an important role in the field of human lighting.
In addition, there are display industries. The current first-generation quantum dot display device is a backlight product combining GaN LED and quantum dots. Both Najing and two high-tech companies in the United States have entered the commercialization stage. This new type of backlight makes display color purity and color saturation very high, which is difficult to match with other display technologies. As far as I know, a large domestic TV manufacturer will launch this new color TV at the end of this year or early next year.
From beginning to boom in the field of quantum dots <br> <br> originator, about in the late 1970s. At the time, chemists in Western countries were affected by the oil crisis and wanted to find a new generation of photocatalytic and photoelectric conversion systems that could use solar energy. Drawing on the principles of semiconductor solar cells, chemists began experimenting with the preparation of small semiconductor crystals in solution and studying their optoelectronic properties. Representative figures include BARD and BRUS in the United States, Ekimov in the former Soviet Union, and HENGLEIN in Germany.
In the lab, the researchers found a very strange phenomenon. For example, the large single crystal of lead sulfide is always familiar black, but the color of the nanocrystals that chemists make in solution is different, some are yellow, some are red, some are black, some are even without color. . What strange things happened?
Finally, the American scientist BRUS, the former Soviet Union's E-FROS gave a beautiful explanation, which is the "quantum confinement effect" theory. The publication time of their articles was somewhat different, but because of the isolation of the former Soviet Union, they did not know each other's work.
So far, chemists are playing a leading role in this field, and synthesizing quantum dots with performance requirements is still the most critical thing in the field. Prior to 1990, synthetic methods were based on traditional chemical methods for preparing colloidal small particles, such as coprecipitation, microemulsions, micelles, and the like. These methods are capable of controlling the size to a desired extent to some extent, but the optical performance is very poor and substantially does not emit light.
A very important thing happened between quantum dot research between 1990 and 1993. A new synthetic method called “metal organic-coordinating solvent-high temperature†was introduced. This method was first used in Bell Labs. Invented, it uses high toxicity and very unstable dimethyl cadmium as a cadmium source to synthesize high quality cadmium selenide at high temperature (about 300 degrees Celsius) and organic coordination solvent. This is a milestone for the entire field. However, this also leaves a challenge for the field. The raw materials they use are borrowed from “metal organic vapor depositionâ€. The dimethyl cadmium is explosive, even at room temperature, and it is very toxic and costly. These factors have led to the development of this field not being fast in the next 10 years, and only one material can be made.
Later, when I arrived at the University of Arkansas, we found a “green†organic solvent route that allowed the simple synthesis of quantum dots to enter laboratories around the world. As long as there is an ordinary chemical synthesis laboratory, it can be done in China. Next, we systematically explored the quantum dot growth mechanism, so that the range of relatively high quality quantum dots is gradually extended to other types of semiconductors. For these reasons, this “green†route is quickly being promoted around the world, including industry and academia.
I believe that scientific research falls into two categories, namely, "forward-looking exploration" and "systematic research." The above-mentioned work of Bell Labs in 1990 is a typical forward-looking exploration, and our laboratory's work in this century is closer to systematic research. The unknown world facing scientific research does not have the standard answer like an exam. Therefore, we can neither deny forward-looking exploration nor despise systematic research. At present, Chinese scientific research has a tendency to place too much emphasis on the former and pay too much attention to scientific hotspots.
Disruptive progress <br> <br> back to Zhejiang University, I slowly realize that quantum dot synthesis chemistry the real core issue is the excited state control. This is because, as a luminescent material, its performance can only be achieved in an excited state. For traditional synthetic chemistry, chemists only care about the ground state. Based on this new understanding, we have adopted some new synthetic control methods. As a result, we have some quantum dots that have never been seen before.
Based on these new quantum dots, we have seen the first subversive quantum dot application by working with the Associate Professor Jin Yizheng and the Najing Technology Company of the Zhejiang University Materials Department. That is the quantum dot LED (QLED) with excellent performance. After applying for a patent, we submitted the first article to Natue magazine. Already published online.
Light-emitting diodes (LEDs) are changing our lives, and energy-saving effects in lighting and display have been recognized, and this is the foundation of this year's Nobel Prize in Physics (GaN-Blue LED). Gallium nitride blue LEDs have been mass-produced, and related intellectual property rights have been firmly controlled by Japanese, American and European companies. However, the technology of GaN blue LED is based on epitaxial growth of a multilayer semiconductor single crystal on a sapphire single crystal substrate, requiring high vacuum equipment, ultra high purity raw materials, and high energy consumption in the preparation process. Therefore, its basic cost is large.
If quantum dot synthesis meets the requirements for LED optoelectronic performance, then quantum dot LEDs are expected to combine the advantages of both GaN LEDs and OLEDs. Our recent work confirms this vision. Nature's reviewers gave several indicators to allow us to make a horizontal comparison with OLED and other solution processing LEDs. The results show that although our QLEDs were prepared by solution method under relatively simple conditions, our devices almost completely outperformed.
LED is also the core component of the lighting industry. But compared with sunlight, the current white LED lamp is defective. It is artificial white light and has many high-energy photons. The impact of high-energy photons on human health has been shown to be unfavorable. In addition, the current white LED fever is more obvious, this is not good news. The white light of QLED can be completely consistent with the ideal illumination source, closer to natural light, and the heat is greatly reduced. The progress of our recent work shows that one day quantum dot LEDs will contribute to the lighting industry. The field of quantum dots has now evolved to a level that requires deeper, more systematic, and more integrated (or more intersecting) levels. Our QLED technology is currently in a leading position in the world and has established its own intellectual property rights. However, competition from MIT (QDVision), SAMSUMG, etc. is not to be underestimated.
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