Optical properties of Si-Ge semiconductor nano-onions

We explore theoretically the possibility of obtaining efficient light emiss ion from Si-Ge semiconductor nano-onions. Our motivation stems from the str ong luminescence recently observed from II-VI nano-onions, combined with th e technological significance of the Si-Ge system. We calculate the electron ic properties of a range of hypothetical Si-Ge nano-onions using the tight- binding method and determine the combination of. size,; strain, and materia ls which optimizes the production of visible luminescence. We predict that small (less than around 30 Angstrom diameter) Si-covered Ge nano-onions wil l be visible light emitters.