Quantum dots: properties, applications, prospects

Quantum dots: properties, applications, prospects

Quantum dot is a nanocrystal of inorganic semiconductor material (silicon, indium phosphide, or cadmium selenide). Prefix “nano” means one billionth part: the size of these crystals vary from 2 to 10 nanometers. Such a small size makes electrons in nanoparticles behave in an unusual way compared to semiconductor particles of regular size. Ability to control the wavelength of emitted light using semiconductor particles resizing allows getting photostable luminophores. Depending on particles’ size, these luminophores in reply to external influences emit light of stable wavelength and particular color. Solutions based on quantum dots exceed traditional organic and inorganic luminophores using a variety of criteria that are important for technologies where precise adjustible luminiscence is necessary. Advantages of quantum dots:
  • Photostable and keep their fluorescent properties for several years. – Higly resistant to light (100-1000 times higher that organic fluorescers).
  • Provide high fluorescence quantum efficiency: up to 90%.
  • Have wide excitation spectrum, from UV to IR (200-1000 nm)
  • Due to narrow peaks of fluorescence (25-40 nm) provide excellent color purity.
  • Higly resistant to chemical degradation.
For printing industry, it is also important that quantum dots may exist as sols – highly refined colloidal fluid system with fine particles distributed. Fluid base can be both water-based and UV-curable, which allows producing different types of ink. Applications of quantum dots: Protection of documents and products against forgery: quantum dots can be applied in color coding of securities, banknotes, identity cards, stamps, seals, certificates, plastic cards, trademarks, and other products in food industry, pharmaceutical or chemical industry, jewelry, art, etc. As stated above, fluid base for the ink made of quantum dots can be various, which allows applying color coding to almost any object. Water-based ink is good for paper and other absorbing materials, while UV-curable ink works with any non-absorbing surface such as glass, wood, metal, synthetic polymers, or composites. Biomarker in medical and biological research. Using quantum dots as fluorescent markers for studying tumor cells in vitro is one of the most promising and rapidly developing fields of application of quantum dots in biomedicine. Quantum dot displays. QLED is a technology of producing LCD displays with LED backlight based on quantum dots. Such technology has several advantages like lower energy consumption, 25-30% larger luminous flux compared to LED displays, more vivid colors, and ability to make displays ultra-thin and flexible. Quantum dots allow LCD displays providing colors as close as possible to natural. In 2013, Sony launched QLED display working on the same basis, but at present moment, the technology of producing wide displays based on quantum dots did not become a common thing due to high production cost. Quantum dot laser. In their light emitting region, quantum dots have several advantages over traditional semiconductor lasers based on three-dimensional structures or quantum wells. Due to the fact that quantum dot’s active region can be changed, along with its size and structure, now there is a possibility to work with such wavelengths that were previously inaccessible. In medicine, this technology got commercial application, which resulted in development of laser scalpel. Energy Colloid quantum dots can be used as an absorption component in thin-film solar panels. Several promising prototypes have been already created: In 2011, there was an idea of “solar paint” based on titanium dioxide, which can transform any object into a solar panel. However, its efficiency was rather low –1% only. In 2014, a group of scientists from MIT presented new method of making solar cells of ultra-thin layers of quantum dots with 9% efficiency. It was a true know-how which allowed combining quantum dots into a film. В In 2015, Laboratory of Center for Advanced Solar Photophysics in Los Alamos suggested a project on turning windows into solar panels, with 3.2% efficiency. Real breakthrough was achieved by scientists from the United States’ National Renewable Energy Laboratorywhile they were searching for the optimal combination of metals in order to create a cell that could provide maximal conversion quantum efficiency. After many experiments they created a panel that demonstrated 114% internal and 130% external conversion quantum efficiency when tested. These numbers do not represent real efficiency of the panel, which is, in fact, relatively low—just 4.5%; however, this was not a key objective of the research. Nevertheless, it is worth noting that no panel before this experiment ever showed conversion quantum activity more than 100%. As we see, fields of application for quantum dots are wide and various, which provides fertile ground for many scientific developments. Their massive introduction yet faces several obstacles such as high production cost, toxicity, inadequate and economically feasible production technology. Increasingly aware of the potential of this promising, knowledge intensive, and still—not occupied market niche, IQDEMY company recognizes production of quantum dot ink as one of priorities for our research activities. President of the IQDEMY Holding Vlad Mirchev: «Quantum dots appear to be a very promising area, and for now, this market is not occupied. In Russia, Nanotech-Dubna company used to be actively engaged in this, but they did not go further than producing quantum dot using the colloidal synthesis method. We, in turn, are making the next step towards commercialization of this technology. Quantum dot ink is going to be in demand now, because the world is facing such acute problems as forgery and fraud: for instance, in 2014, credit card fraud resulted in losses amounting to 3.5 billion rubles. With appropriate ink and coding systems, we can start producing unique cards with protection against forgery immediately— since UV-printers already make that possible. Another important thing is that it is a rather cheap production which can make a product truly unique and fraud resistant. » At present, specialists of IQDEMY chemical research laboratory are working to create the optimal formulation of UV-curable ink and water-based ink made of quantum dots.

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