Contributed by Daniel Daniel
Quantum dot is a semiconductor crystal, which has electronic properties intermediate between those of bulk semiconductor and those of discrete molecules. The electronic properties of quantum dot are closely related to the size and shape of the individual crystal. Generally, the smaller the crystal, the larger the band gap and the larger is the energy transition between the highest valence band and the lowest conducting band. A main advantage of quantum dot is that because the size of the crystal can be exquisitely controlled, the electronic properties of quantum dots can similarly be tuned precisely.
Physics of quantum dot
In bulk semiconductor, an electron-hole pair is typically bound with a characteristic length, called the exciton bohr radius. The electron-hole pair forms an unconfined hydrogen-like energy states. When the size of the crystal approaches that of the bohr radius, the electron and hole pairs become confined and the properties of the semiconductors change dramatically. A typical size of a quantum dot is of the order of several nms and there is confinement in all three spatial dimensions.
Quantum dots can be used for various optical devices such as dye because of its superior optical properties. Quantum dots are much brighter than conventional fluorescent dyes (up to 20 times brighter) and are resistant to photobleaching. Though, one persistant issue that prevents its use in vivo is its toxicity. There have also been developments to use quantum dots as photovoltaic and light emitting devices. Quantum dots have also been suggested to be used as qubits in quantum computing.