Using C-60 molecule as a kind of surface-passivated agent to modify the electronic structure of Si nanocrystallites in porous silicon, we disclose that this kind of C-60/nanocrystalline Si coupling system can show a strong blue emission at similar to460 nm when stored in air for more than one year. After a full characterization of the photoluminescence properties, we propose a luminescent center in the SiOx layer at the surface of a Si nanocrystallite. It is a pair consisting of an oxygen vacancy and an interstitial oxygen. The interstitial oxygen also forms a peroxy linkage with a neighboring lattice oxygen. Radiative recombination of carriers photogenerated from Si nanocrystallite cores in the luminescent centers results in the observed blue photoluminescence. Neutron irradiation experiments support our assignment of the blue emission mechanism. This work improves the understanding of the origin of blue emission from silicon/oxygen-related nanostructured materials. (C) 2004 American Institute of Physics.