Optical properties of germanium nanocrystals

We study the electronic structure and the optical properties of germanium c lusters up to about 10(3) atoms, by using a semi-empirical tight-binding ap proach. Germanium nanocrystals are related to quantum dots growing, by a se lf-organization process, in sapphire matrices. The optical properties of su ch dots are experimentally found to be strongly influenced by quantum confi nement effects.. We investigate these effects from the theoretical point of view, calculating the optical spectra in the single-particle approximation . Inclusion of the electron-hole interaction is found to yield visible effe cts.