Picture: Colloidal quantum dots irradiated with a UV light. Different sized quantum dots emit different color light due to quantum confinement.
Quantum dots are constructed of a few hundred atoms, yet have all the quantum properties of a single atom. Some have been designed to reveal the workings of the nervous system, and others to be the detectors of breast cancer.
They’re zero dimensional, so they have less density than higher-dimensional structures. As a result, they have superior transport and optical properties, and are being researched for use in diode lasers, amplifiers, and biological sensors.
Researchers have tested them in transistors, solar cells, LEDs, and diode lasers. They have investigated them as agents for medical imaging and hope to use them as qubits ( qubit- In a classical system, a bit would have to be in one state or the other, but quantum mechanics allows the qubit to be in a superposition of both states at the same time).
In fluorescent dye applications, higher frequencies of light emitted after excitation of the dot as the crystal size grows smaller results in a color shift from red to blue in the light emitted.
An immediate optical feature of colloidal quantum dots is their coloration. Quantum dots of the same material, but with different sizes, can emit light of different colors. This is the quantum confinement effect. The larger the dot, the redder (lower energy); Conversely, smaller dots emit bluer (higher energy) light.Quantitatively speaking, the energy (and hence color) of the fluorescent light is inversely proportional to the size of the quantum dot
Quantum dots of different sizes can be assembled into a gradient multi-layer nanofilm —- Properties of such nanostructures are finding its applications in design of solar cells and energy storage devices.
In an unconfined semiconductor, an electron-hole pair is given a characteristic length, called the exciton Bohr radius. This is estimated by replacing the positively charged atomic core with the hole in the Bohr formula. If the electron and hole are constrained further, then properties of the semiconductor change. For example, the absorption and emission wavelength of light shifts towards smaller wavelengths. This effect is a form of quantum confinement, and it is a key feature in many emerging electronic structures.
Lee et al. (2002) reported using genetically engineered M13 bacteriophage viruses to create quantum dot biocomposite structures. It is known that liquid crystalline structures of wild-type viruses (Fd, M13, and TMV) are adjustable by controlling the solution concentrations, solution ionic strength, and the external magnetic field applied to the solutions.