A quantum dot gets its name because it’s a tiny speck of matter so small that it’s effectively concentrated into a single point (in other words, it’s zero-dimensional). As a result, the particles inside it that carry electricity (electrons and holes, which are places that are missing electrons) are trapped (“constrained”) and have well-defined energy levels according to the laws of quantum theory (think rungs on a ladder), a bit like individual atoms. Tiny really does mean tiny: quantum dots are crystals a few nanometers wide, so they’re typically a few dozen atoms across and contain anything from perhaps a hundred to a few thousand atoms. They’re made from a semiconductor such as silicon (a material that’s neither really a conductor nor an insulator, but can be chemically treated so it behaves like either). And although they’re crystals, they behave more like individual atoms hence the nickname artificial atoms.
Quantum dots were discovered in the 80’s but commercialization has initially been slow. Interest in quantum dots peaked in the early 2000’s when nanotechnology was still a favorite keyword amongst investors. However, a lack of products meant that quantum dots were mostly used in research labs.
In the last three years, quantum dots have been back in the spotlight with the promise to make LCD screens more colorful and more energy efficient. Sony was the first to commercialize a quantum dot LCD TV in 2013 and there are now several OEMs (including Samsung) offering TVs with quantum dots.
As a type of semiconductor, quantum dot exhibit a photoluminescence which is particularly useful for improving colors in LCD. But quantum dots can also be used as electroluminescent materials: quantum dot light emitting diodes (QLED) have been in development for several years and they have a great potential for display applications. Quantum dots are also emerging as a promising material for other type of devices, most notably optical and infrared sensors.
These tiny nanoparticles have diameters which range from 2 nanometers to 10 nanometers, with their electronic characteristics depending on their size and shape. Nanoshel are able to accurately control the size of a quantum dot and as a result they are able ‘tune’ the wavelength of the emitted light to a specific colour.
Quantum dot find applications in a number of areas such as solar cells, transistors, LEDs, medical imaging and quantum computing, thanks to their unique electronic properties. Nanoshel deals with the quantum dots such as
- CdTe quantum dots, powder, hydrophilic – CdTe quantum dots exhibit the broadest wavelength emission spectra range between 510 nm and up to 780 nm. It is easy to form colloidal solutions of them in water and terminate them with -COOH group. It is possible to couple -NH2 groups with them through EDC-mediated esterification. They are suitable for biologic labeling purposes.
- CdSe/ZnS (core/shell) quantum dot, powder, hydrophobic – CdSe/ZnS quantum dots are core-shell structured inorganic nanocrystals wherein an outer core of wider band gap ZnS encapsulates an inner core of CdSe. They are highly luminescent semiconductor nanocrystals coated with hydrophobic organic molecules. They are insoluble in ethers, alcohols and water, but soluble in pyridine, tetrahydrofuran, chloroform, toluene, heptanes, and hexane. The wavelength emission spectra range between 530 and 650 nm.
- ZnCdSe/ZnS (core/shell) quantum dots, powder, hydrophobic – ZnCdSe/ZnS quantum dots have the smallest available average particle size. Thus, they can emit the bluest to white light, making them suitable for use in solid state luminescent devices. Wavelengths range from 440 to 480 nm. They are highly luminescent semiconductor nanocrystals coated with hydrophobic organic molecules. They are soluble in pyridine, tetrahydrofuran, chloroform, toluene, heptanes, and hexane, but insoluble in ethers, alcohols and water.
Applications of Quantum Dots
Light Emitting Diodes
Quantum dot light emitting diodes (QD-LED) and ‘QD-White LED’ are very useful when producing the displays for electronic devices due to the fact that they emit light in highly specific Gaussian distributions. QD-LED displays can render colors very accurately and use much less power than traditional displays
Quantum dot photo detectors (QDPs) can be produced from traditional single-crystalline semiconductors or solution-processed. Solution-processed QDPs are ideal for the integration of several substrates and for use in integrated circuits. These colloidal QDPs find use in machine vision, surveillance, spectroscopy, and industrial inspection.
Quantum dot solar cells are much more efficient and cost-effective when compared to their silicon solar cells counterparts. Quantum dot solar cells can be produced using simple chemical reactions and can help to save manufacturing costs as a result.
The latest generation of quantum dots has great potential for use in biological analysis applications. They are widely used to study intracellular processes, tumour targeting, in vivo observation of cell trafficking, diagnostics and cellular imaging at high resolutions.
Quantum dots have been proved to be far superior to conventional organic dyes as a result of their high quantum yield, photo stability and tunable emission spectrum. They are 100 times more stable and 20 times brighter than traditional fluorescent dyes.
The extraordinary photo stability exhibited by quantum dots make them ideal for use in ultra-sensitive cellular imaging. This allows several consecutive focal-plane images to be reassembled into three-dimensional images at very high resolution.
Quantum dot can target specific cells or proteins using peptides, antibodies or ligands and then observed in order to study the target protein or the behavior of the cells. Researchers have found out that quantum dots are far better at delivering the siRNA gene-silencing tool to target cells than currently used methods.