SiOx nanoparticles were prepared by vaporisation and condensation of melted silicon droplets put on zirconia pellets in a solar reactor at the focus of a 2 kW solar furnace. The size of the grains were nanometric, generally included in the range 20-40nm, and the O/Si atomic ratio values were close to stoichiometry (O/Si approximate to 1 +/- 0.2). XPS, DRX and TEM analyses show that these nanoparticles are amorphous with various silicon chemical environments which can be described as constituted with polysubstituted Si-(O4-nSin) tetrahedral configurations. The estimated oxygen atomic concentrations for these nanoparticles was in good agreement with thermodynamic equilibrium calculations for the system ZrO2-Si at high temperature. The predominant gaseous species is the SiO molecule. The SiO2 nanoparticles present photoluminescence property similar to those currently reported for electrolytic porous silicon. (c) 2004 Elsevier Ltd. All rights reserved.