Synthesis and photoluminescence of web-like agglomeration of silica nanoparticles

The development of new methods for the synthesis of nanoparticles that possess unique properties and morphologies is of considerable interest in a number of fundamental scientific disciplines as well as for practical applications. Here, we show that silica nanoparticles, produced by laser vaporization of polycrystalline silicon in a He/O{sub 2} atmosphere in a diffusion cloud chamber, aggregate into a novel web-like microstructure. These aggregates are very porous and have a very large surface area (460 m{sup 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{sub 2}{sup o} 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{sub 2}{sup o} defect which in turn gives rise to the observed bright photoluminescence. This material could have special applications in optical devices, catalysis and as a polymer reinforcing agent.