Silica nanoparticles, produced by laser vaporization of polycrystalline silicon in a He/O-2 or Ar/O-2 atmosphere in a diffusion cloud chamber, aggregate into a novel weblike microstructure. These aggregates are very porous and have a very large surface area (460 m(2)/g). Bright blue photoluminescence from the nanoparticle silica has been observed upon irradiation with UV light. The photoluminescence is explained by the presence of intrinsic defects of the type Si(II)(0) in the amorphous silica. It is proposed that the laser ablation of Si in oxygen as described here results in a silica nanostructure with a large concentration, especially at its internal surfaces, of this Si(II)(0) defect which in turn gives rise to the observed bright photoluminescence. This material could have special applications in optical devices and catalysis and as a polymer reinforcing agent.