Quantum Dots (QD), nanoparticles of semiconductors, were theorized in the 1970s and initially created in the early 1980s. If semiconductor particles are made small enough, quantum effects come into play, which limit the energies at which electrons and holes (the absence of an electron) can exist in the particles.
They display unique electronic properties, intermediate between those of bulk semiconductors and discrete molecules.
Their diameters is in the range of 2-10 nanometers (10-50 atoms).