Quantum Dots applications fill the advance fields of biomedical, electronics, pharmaceuticals, Textile, , etc. for having excellent properties. Quantum Dots applications created a great revolution in the field of Nanotechnology. It involves nanoscale manipulation of atoms and molecules. It is also known as semiconductor nanocrystals. Quantum Dots applications especially focus on a wide variety of fields of medical diagnostics, drug delivery, gene therapy, etc.
What are quantum dots?
Quantum dots or QDs are called nanocrystals of a semiconductor material containing a size less than 10 nm. At present, quantum dots are becoming attractive nanocrystalline materials for different applications. QDs have special characteristics like attractive optical, electronic, and chemical properties. So, Quantum dots applications are becoming popular for making photodetectors, displays, solar cells, wastewater treatment, biosensors, and quantum computers.
Quantum dots definition
Quantum dots or QDs are important semiconductor-type nanoparticles having sizes ranging from a few nanometers to tens of nanometers. It comprises special characteristics like good optical, electronic, and chemical properties. As a result, QDs are used very much to make attractive electronic devices, including solar cells, LEDs, and transistors in the fields of electronics. Quantum Dots applications create a great dimension in the fields of biomedical to conduct live imaging, drug delivery, and medical diagnosis, in addition to other applications beyond medicine such as in solar cells.
What are the examples of Quantum dots?
Quantum dots or QDs are very tiny nanocrystalline materials having diameters in the range of 2nanometers to 10 nanometers (10-50 atoms). Quantum dots or QDs are popular materials nowadays. They are found in tools of cell biology and medical diagnostics. The apparatus or various tools in the fields of biomedical need QDs due to contain various attractive optical properties, including bright and stable fluorescence.
Quantum dots example
Quantum dots or QDs nanoparticles are found in television backlighting, photodetectors, LEDs, various electronic displays, and photovoltaics. Quantum dots applications include security printing, anti-counterfeiting measures, tracking, and tracing purposes.
What is the structure of Quantum dots?
Quantum dots have a core and shell. The core of the QDs is made of special semiconductor material. The shell of the outermost layer is generally constructed by an aqueous organic coating.
Quantum dots structure
A quantum dots structure comprises an inorganic core semiconductor material that is overlapped by an aqueous organic coating. The most used semiconductor materials to make this core are CdTe or CdSe, and an inorganic shell of a different band gap such as ZnS. It is very essential to select the suitable materials for constructing the shell and core. The suitable materials are responsible for making QDs more outstanding. Quantum dots or Q dots have the ability to alter the photophysical properties at the time of coating.
Working Principle of Quantum dots
Quantum dots working principle relates the valence band holes and conduction band electrons. These bands have a distinct energy level that carries the electricity. It is possible to occupy the electrons in different bands into different bands of QDs that ‘fit’ inside it. These bands emit photons during the excitation of the electrons. It is noted that this excellent phenomenon occurs when QDs come in contact with a light or electricity source. It is seen in the red light from the biggest-size QDs during the emission of the longest wavelengths of light. It is also seen in the blue light from the smallest size QDs during the emission of the shortest wavelengths of light. Quantum Dots applications create a new dimension in the different fields of nanotechnology.
How Quantum dots are synthesized?
Quantum dots synthesis methods are Top-Down and Bottom-Up methods. The bulk materials are thinned mechanically to synthesize QDs in the top-down method, whereas molecular beam epitaxial growth and colloidal synthesis methods are used in the bottom-up method.
Quantum dots synthesis
Quantum dots or QDs nanoparticles are synthesized by various chemical, mechanical, and physical methods. Electron beam lithography, reactive ion etching, focused beam lithography, and dip pen lithography techniques are used to synthesize quantum dots by top-down method. This method may create various structural imperfections caused by patterning and contamination.
In the bottom-up synthesis process various chemical and physical methods to form Quantum dots nanoparticles.
The molecular beam epitaxial growth method and colloidal synthesis methods are used to synthesize QDs nanoparticles in a bottom-up process.
The popular synthesis method of Quantum dots
At first, 0.02 M Cd(ClO4)2.H20 compounds are dissolved into distilled water. Then the solution must be stirred properly after adding thiol as a stabilizer. Then NaOH solution must be added to control the pH level. It should be deaerated by N2 bubbling for 30 minutes. Then, we get QDs nanoparticles after heating, cooling, and separating properly.
What are the properties of Quantum dots?
Quantum dots are special type man-made nanoparticles having sizes normally no more than 10 nanometers.QDs have a small size and contain special features. Quantum dots have excellent optical properties, electronic properties, chemical properties, high quantum yield, high photostability, and higher molar extinction coefficients. Quantum Dots applications are increasing day by day for having these attractive properties.
Quantum Dots physical properties
Quantum dots or QDs have excellent morphological features. Quantum dots nanoparticles show amazing dispersibility, biocompatibility, strong optical properties, and magnetism behavior. The size of quantum dots can be controlled enabling them to reflect various strong and tunable fluorescent properties. These attractive properties lead to making PbS, CdS, silicon-based QDs, graphitic carbon nitride QDs, molybdenum disulfide QDs, and various QDs-based components.
Quantum Dots chemical properties
Quantum dots chemical properties relate to the unique chemical compositions of the core, shell, and ligands, which provide them with excellent properties for different types of applications.
There exist various chemical compositions of the core, shell, ligands, structures, and coordination numbers that are responsible for focusing various chemical properties. Quantum dots have outstanding stability, oxidation, reactivity, and thermodynamic and kinetic properties to lead the various better forms of character.
Quantum dots nanoparticles can be altered easily with the help of different chemical coatings. QDs particle has higher stability and do not degrade over time. QDs have high charge carrier mobility. It is the energy gap between the highest occupied electron orbital and the lowest unoccupied orbital in the QDs system. Quantum Dots applications are very much increasing for having these chemical properties.
Quantum dots chemical stability
Quantum Dots or QDs nanoparticles are very compatible with the desired matrix or host material. QDs show various excellent chemical and physical properties. The compatibility of QDs is very essential property for device integration and stability.
Other Properties of quantum dots
Quantum dots properties include smaller size, higher brightness, tunable composition and properties, high photostability, higher quantum yield, and intermittent light emission. These properties make this nanocrystalline material more attractive for different types of applications.
Quantum dots particle size
Quantum dots particle size is generally less than 10 nanometers. Quantum dots or QDs nanoparticles are very tiny particles that have radii generally 2nm to 9 nm sizes. As a result, Quantum dots emit wavelengths that produce various colors such as violet, blue, green, yellow, orange, or red. Smaller size quantum dots with a radius of 2nm to 3 nm emit smaller wavelengths creating colors such as violet, blue, or green. Larger size quantum dots with a radius of 5nm to 6nm produce wavelengths generating colors like yellow, orange, or red.
Quantum dots Optical Properties
Quantum dots optical properties focus the intrinsic band gap into nanoparticles. So, the electrons in QDs are able to be excited from the valence to the conducting band by absorbing incident light and leaving behind a hole. The excited electrons in the conducting band and holes form an exciton state. When the excited electron returns to its ground state, a longer wavelength from the photons will be emitted. This phenomenon of electronic state is known as Fluorescence. It is generally seen that the larger size band gaps are created by the smaller-sized QDs.
Quantum dots Electrical Properties
Quantum dots electrical properties are concerned with zero-dimensional electron systems. A few numbers of electrons are confined in very small areas of QDs.Quantum mechanical tunneling can be found that consists of weakly linked QDs. Electrical transport through single atoms or molecules into QDs occurs. This phenomenon can be controlled electrostatically by nearby gate electrodes.
QDs system is fabricated easily by conventional semiconductor growth and processing technology. But it is needed lower temperatures to control their mesoscopic size.
It is coulomb blockade and single-electron charging in QDs for the creation of repelling electrostatic electron-electron interaction. As a result, QDs system acts as single-electron transistor systems. The electron’s spin orientation up or down can be seen in QDs for reducing the temperature in peculiar quantum dynamics. If the two quantum dot systems are arranged systematically, they will behave as a pseudo-spin Kondo system.
Quantum dots Electronic Properties
Quantum Dots electronic properties are derived by the interaction of magnetic double barriers in quantum wires. QDs regarded as quasi-zero-dimensional semiconducting systems. This system can be tuned electrostatically by nanopatterned gate electrodes.
Quantum dots nanomaterials show good electrical conductivity and charge carrier mobility. Having these characteristics, QDs are used very much to make electronic devices or solar cells.
Quantum Dots Magnetic Properties
Quantum Dots magnetic properties are associated with various magnetic dimension-dependent properties. They have the ability to bioconjugate for intracellular tagging, contrast-improving agents in magnetic resonance imaging, targeted drug delivery magnetic separation, etc. Quantum Dots can combine a magnetic moment and fluorescence. QDs have the ability to allow magnetic separation and imaging benefits.
What are the uses of quantum dots?
Quantum dots are used in different fields of Nanotechnology. QDs are used to make various composites, solar cells, screens, quantum computers, bioimaging, photovoltaic devices, LEDs, etc for having versatile properties.
Quantum Dots applications in Different fields
There are various applications of quantum dots in different fields which are discussed below:
Quantum Dots Applications in Nanotechnology
Applications of Quantum Dots in Nanotechnology relate the most modern invention of electronic displays to biomedical treatments. They fill the fields of Nanotechnology for having excellent optical and electrical properties.
The energy level in Q dots lies between a single atom and a solid and it contains discrete energy levels that are separate from one another and can be counted. They are used in the fabrication of infrared detectors in the fields of Nanotechnology.
Quantum Dots Applications in Electronics
Quantum Dots applications in electronics are the making of various electronic instruments for use in different fields. QDs are used very much to make light-emitting diodes (QD-LED) and ‘QD-White LED’. These LED lights are very effective at the time of producing the displays for electronic devices. QD-LED emits light in highly specific Gaussian distributions.
Modern photodetectors can be produced from quantum dots. These QDs are essential for the integration of several substrates and for use in integrated circuits. The colloidal Quantum dot photodetectors are used in machine vision, surveillance, spectroscopy, and industrial inspection.
Quantum Dots applications are associated make photovoltaic devices like Quantum dot solar cells. These cells can be prepared using simple chemical reactions and can help to save manufacturing costs as a result.
Quantum Dots Applications in Medicine
Quantum dots applications in medicine relate to preparing various types of medicine that are used in many respects. QDs are used for bioimaging applications purpose. QDs are used to make excellent biosensors that are used for proper observation of cell trafficking, diagnostics, and cellular imaging at high resolutions. Quantum dots have attractive properties and have the ability to target specific cells or proteins using peptides, antibodies, or ligands. They are also used to study the target protein or the behavior of the cells. QDs are also gaining popularity to treat antibiotic-resistant infections.
Quantum Dots Applications in Biology
Quantum dots application in biology is concerned with the matter of safety and biocompatibility. It may cause toxicological effects due to exposure to some novel nanomaterials, such as gold nanoparticles and QDs. The quantum dots of CdSe core release the free Cd2+ ions due to the deterioration of QDs lattice. It may create harmful effects on the primary cells of the liver. It is found that the CdSe/ZnS and CdTe/ZnS/TEOS core/shell of quantum dots lead to cytotoxicity because of releasing minute-size nanoparticles. The smallest diameter of quantum dots releases various nanoparticles and leads to adverse tissue reactions among cellular components and proteins.
Quantum dots act as good transmission media to transport the various substances inside the body or specific organ where it is needed. Quantum dots have good water-soluble properties, better biocompatibility, and a controlled release profile of drugs at target sites.
Quantum Dots Applications in Textile Industries
Quantum dots applications in Textile industries are concerned about the most uses of N-GQD (Nitrogen-doped graphene quantum dots) and titanium dioxide (TiO2) NPs. These nanocrystalline materials have anti-UV radiation properties that act as important barriers to preventing aging, burns, blemishes, or even cancer. The nano-coating on various fabrics like cotton fabric obtained from N-GQD (Nitrogen-doped graphene quantum dots) and titanium dioxide (TiO2) NPs have excellent UV absorbers and their ultraviolet protection factor (UPF). QDs have the ability to resist UVA (400–320 nm), UVB (320–290 nm), and UVC (290–190 nm).
The nanomaterials on surface coating of various fabrics obtained from QDs prevent DNA damage, chemical and histological changes in the epidermis, extracellular, collagen degradation in the human body, and pathway activation of intracellular signaling involved in photocarcinogenesis and photoaging.
A lot of studies found that QDs nanoparticles from SiO2, TiO2, ZnO, CuO, and Ag improve the UV protection properties of fabrics. Among these TiO2 is used very much in textile industries for having UV protecting properties, higher efficiency, higher chemical stability, and higher light resistance abilities in textile fabrics. QDs have anatase and rutile phases due to the presence of their gap energy (3.192 eV) and protect against UVA/UVB radiation. It is also noted that QDs in textile fabrics have a lower scattering effect in the region visible, with little filtering of this region.
What are the types of Quantum dots?
There are three types of Quantum dots namely core types Quantum dots, core-shell Quantum dots, and alloyed Quantum dots.
Types of Quantum dots
Quantum dots types are classified into three categories on the basis of their composition and structure. The discussions about the three types of quantum dots are given below:
Core-type Quantum dots nanoparticles
Core type Quantum dots consist of single-component materials with uniform internal compositions. It can use cadmium, lead, or zinc element as the single component materials. Core type Quantum dots have photo- and electroluminescence properties which can be tuned by simply changing the size.
Core-shell type Quantum dots nanoparticles
Core shell-type Quantum dots are constructed by the combination of higher band gap semiconducting materials. Core shell-type Quantum dots contain luminescent properties that derive from the recombination of electron-hole pairs through radiative pathways. Examples of core shell-type Quantum dots are CdSe in the core and ZnS in the shell.
Alloyed-type quantum dot nanoparticles
Alloyed-type quantum dots are made by alloying together two semiconductors with different band gap energies. These QDs emit light of different wavelengths and contain composition-tunable properties.
The Future of Quantum Dots
The future of Quantum dots is very exciting because of having a sharper density and near the zero-dimensional figure. Quantum dots (QDs) contain excellent optical and transport properties. QDs are widely used in the fields of biomedical, electrical, electronics, pharmaceuticals, textiles, etc. Quantum dots are very effective particles in cancer metastasis, lymphocyte immunology, embryogenesis, and stem cell therapeutics.
What are carbon quantum dots?
Carbon quantum dots or CQDs are crystalline nanomaterials having particle sizes of 1 nanometer to 10 nanometers. Carbon quantum dots or CQDs contain outstanding electrical /thermal conductivity, high plasticity, and corrosion-resistant properties.
Carbon Quantum dots
Carbon Quantum dots are effective nanoparticles obtained from carbon-based materials having UV-blocking, higher adsorption rate, and higher temperature resistance properties. Carbon quantum dots or CQDs like graphite sheets are composed of sp2 carbon atoms formed in planes. Each atom of graphite sheets is bound to the three nearest neighbors 120 degrees apart. Nowadays, carbon quantum dots or CQDs are widely used to make super-capacitors, batteries, fuel cells, transistors, biosensors, etc. for having outstanding properties.
Conclusions
Quantum dots are essential semiconducting nanocrystalline materials having unique optoelectronic properties. QDs are used very much for fabricating various devices, developing nanocomposites, and the fields of the electronic kingdom. Quantum Dots applications are increasing day by day due to having various excellent properties and being used for the development of medical diagnostics, drug delivery, gene therapy, etc.
At present, these nanoparticles are used for multitasking purposes such as in the fields of medicine, electronics, textiles, electrical, optical fields, etc. Researchers are trying to develop QDs for creating a new era in different fields. Nowadays, Quantum dots applications relate to medical diagnostics, drug delivery, gene therapy, etc. in the biomedical sector. So, It can be noted that Quantum dots applications are part and parcel of the fields of Nanoscience.
References
Bera, D., Qian, L., Tseng, T. K., & Holloway, P. H. (2010). Quantum dots and their multimodal applications: a review. Materials, 3(4), 2260-2345.
Reshma, V. G., &Mohanan, P. V. (2019). Quantum dots: Applications and safety consequences. Journal of Luminescence, 205, 287-298.
Lim, S. Y., Shen, W., & Gao, Z. (2015). Carbon quantum dots and their applications. Chemical Society Reviews, 44(1), 362-381.
