Web-like aggregates of Si nanocrystals produced by laser vaporization-controlled condensation technique are allowed to oxidize slowly in air and the photoluminescence (PL) is measured. A significant shift in the PL red band from 1.83 to 1.94 eV is observed. The bonding structure is established by correlating the PL data with the photon-yield electronic structure measurement's using soft-X-ray fluorescence (SXF) and photon-yield near-edge X-ray absorption fine structure (NEXAFS) techniques. The results indicate that as the nanoparticles oxidize, the radius of the crystalline core decreases, which gives rise to a larger bandgap and consequently to the observed blue shift in the PL band.