Nature of luminescent surface states of semiconductor nanocrystallites

We present semiempirical tight-binding and ab initio local density calculations demonstrating the (meta)stability of self-trapped excitons at the surface of silicon nanocrystallites; These are obtained for dimer bonds passivated, for instance, by hydrogen atoms or by silicon oxide. Light emission from these trapped excitons is predicted in the infrared or in the near visible. We are thus led to the interpretation that part of the luminescence is due to such surface states while optical absorption is characteristic of quantum confinement effects. These conclusions should extend to other semiconductor crystallites.