The photochemical aspects of semiconductor nano-particles are of outmost importance for the qualities and the behavior of many coatings. Only the combination of these words is not so often used to describe the numerous coatings whose behaviour, intentionally or not, depends on the photochemical properties of the semiconductor particles they contain.
A semiconductor is a material with an electrical conductivity that is intermediate between that of an insulator and a conductor. Well-known semiconductors in electronics are e.g. silicon, germanium, galliumarsenide, indiumphosphide … but, in general, zinc oxide, aluminumoxide, zincsulphide, silverbromide, titaniumdioxide and many other inorganic compounds are semiconductors too.
A semiconductor has a band-gap ( the energy difference between the conduction band and the valence band) which is small enough that the conduction band can be partially filled with electrons by thermal agitation or by a photonic impact.A semiconductor has a band-gap between 0 and 4 eV.