Semiconducting quantum dots are three-dimensional nanometric inclusions in a material with a small band gap in another material (the matrix) with a larger band gap. Because of their original physical properties, they have been the subject of advanced studies for around 20 years.
These properties are essentially the result of the tight three-dimensional confinement of the charge carriers in the quantum dots leading to a discrete density of electronic states being observed. Quantum dots are quite often considered to be "artificial atoms".