Produkujemy nieorganiczne nanomateriały krystaliczne (nanokryształy) wykonane z materiałów półprzewodnikowych. Ich wielkość waha się w granicach 2-10 nm, co ma niebagatelne znaczenie. W zależności od rozmiaru, QNA.dots absorbują/emitują światło o różnej barwie (energii).
What are quantum dots?
They are inorganic crystalline nanomaterials (nanocrystals) made of semiconductor materials. Their size ranges from 2 to 10 nm, which is of no small importance. Depending on the size, quantum dots absorb/emit light of different colour (energy). The smaller the nanocrystal, the more considerable the blueshift of the emitted light, whereas the redshift (up to the infrared) is observed for bigger nanocrystals.
Quantum dots can absorb light and convert it into electricity (photovoltaics), but they can also convert electricity into light (diodes, displays). They can also convert one colour of radiation into another (radiation converters).
The main goal of reducing the size of semiconductor materials to the nano scale is the use of their new properties, which only appear when the size of the material is comparable to the size typical of the desired physical phenomenon. For example, in order to use the new properties of nanocrystals for optical applications, their size should be comparable to the physical quantity that is characteristic of such properties, e.g. de Broglie wavelength or, more precisely, the exciton Bohr radius, aB). For most semiconductor materials, this is the size of 0.5–20 nm. Once this size limit is exceeded, nanocrystals display new, quantum optical properties: the emission colour is size-dependent, and the emission intensity increases. When such a quantum nanocrystal is spherical in shape, we call it a quantum dot.
The above-mentioned size criterion makes it possible to distinguish between quantum nanostructures and materials that are commonly known as ‘nanopowders’.
The size is a necessary but by no means sufficient criterion for observing quantum effects in nanocrystals, because other effects that are present in the nano scale can actually disturb the quantum effects obtained by size reduction. In particular, in the nano scale, the surface of nanomaterials and everything that happens on it are very important. An important role of the surface is connected with a high surface-to- nanoparticle volume ratio. Therefore, a necessary prerequisite for obtaining the highest quality quantum dots is not only full control over the growth technology, but also over the physical and chemical properties of the surface.
Does it sound quite complicated?
Because, in fact, it is. The technology of obtaining colloidal quantum dots is much more difficult compared to that needed to obtain ‘nanopowders’. Colloidal quantum dots are characterised by a better defined size, controlled distribution of sizes, and a higher quality surface. All these properties guarantee a spectrally narrow and efficient emission. Depending on the applications required, the surface of colloidal quantum dots may be subject to modification which, if carried out in a correct way, makes it possible to maintain the highest quality of quantum dots, including their high dispersibility in both organic and aqueous solvents without sticking.
The synthesis of high quality colloidal quantum dots remains a major challenge for many companies due to the repeatability, scalability and stability issues, as well as the need to maintain high emission efficiency. In order to overcome such challenges, QNA has built a unique research and development team with many years of experience in the synthesis and testing of nanomaterials. Together, we have created a repetitive, scalable and financially efficient production process for colloidal semiconductor quantum dots.
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QNA.dots vs organic dyes
In recent years, we have been observing a rapid development of electronics, photonics and optoelectronics based on organic materials. The most obvious outcome of the process are commonly available OLED displays (TV sets). Organic materials are relatively inexpensive, lend themselves well to making large-format components, and offer considerable mechanical flexibility and functionality. However, they are by no means a perfect solution. In fact, they entail a number of significant disadvantages, such as low resistance to environmental factors, limited durability in time, large manufacturing costs of the end device, and unsatisfactory physical parameters. That is why the global industry is now interested in inorganic semiconductor nanostructures – quantum dots, which are devoid of the above-mentioned limitations.
A wide range of colours
- narrow emission from a wide spectral range (350–2000 nm), corresponding to the range from UV to infrared
- wide absorption in the spectral range (350–2000 nm), corresponding to the range from UV to infrared
Clean, spectrally saturated colours
- narrow (< 30 nm) emission lines
- precisely defined emission wavelength
- high emission efficiency (> 50%)
- emission efficiency for selected wavelengths up to 95%
High luminescence stability:
- very high emission stability over time, even during long-term and intensive UV exposure
- high resistance of optical properties to temperature (up to 300 °C) and other environmental factors
Broad functionality in various applications:
- a large active surface and a possibility to control surface functional groups so that dots can be chemically attached to other objects
- a broad, non-selective absorption spectrum