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Quantum dots have been gaining interest from the scientific community because of their interesting optical properties, the main being band gap tunability. When an electron is excited to the conduction band, it leaves behind a vacancy in the valence band called hole .
In a regular semiconductor crystal, the band gap is fixed owing to continuous energy states. In a quantum dot crystal, the band gap is size dependent and can be altered to produce a range of energies between the valence band and conduction band. [12] It is also known as quantum confinement effect.
Silicon quantum dots are metal-free biologically compatible quantum dots with photoluminescence emission maxima that are tunable through the visible to near-infrared spectral regions. These quantum dots have unique properties arising from their indirect band gap , including long-lived luminescent excited-states and large Stokes shifts .
The Brus equation or confinement energy equation can be used to describe the emission energy of quantum dot semiconductor nanocrystals in terms of the band gap energy E gap, the Planck constant h, the radius of the quantum dot r, as well as the effective mass of the excited electron m e * and of the excited hole m h *.
With their patented continuous flow production process for perovskite quantum dots, [32] QMC hopes to lower the cost of quantum dot solar cell production in addition to applying their nanomaterials to other emerging industries. QD Solar takes advantage of the tunable band gap of quantum dots to create multi-junction solar cells.
Another type of quantum dot composed of indium is the InP quantum dot. Due to the lower photoluminescent intensity and the lower quantum yield of InP they are coated with a material with a larger band gap like ZnS. [22]
In semiconductors, the band gap of a semiconductor can be of two basic types, a direct band gap (DBGSC) or an indirect band gap (IDBGSC). The minimal-energy state in the conduction band and the maximal-energy state in the valence band are each characterized by a certain crystal momentum (k-vector) in the Brillouin zone. If the k-vectors are ...
where k is a vector (called the wavevector), n is a discrete index (called the band index), and u n,k is a function with the same periodicity as the crystal lattice. For any given n, the associated states are called a band. In each band, there will be a relation between the wavevector k and the energy of the state E n,k, called the band dispersion.
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