Bismuth-covered silicon nanocrystalline quantum dots, depending on size and coverage, are predicted to exhibit characteristics of magnetic nanoparticles and luminescent semiconductor dots, accompanied by manifestations of metal-insulator transition. These properties, emerging from accurate time-dependent and standard density functional theory calculations can be critical for the development of nanoscale optoelectronic and opto-magnetic switches, and in quantum computing. (C) 2011 Elsevier B. V. All rights reserved.