Frequency shift in the photoluminescence of nanometric SiO_x: Surface bond contraction and oxidation

The frequency of photoluminescence is determined by the gap between the conduction and valence band. The width of the band gap depends on the crystal field and the chemical reaction, because the crystal field defines the band structure and the reaction repopulates with valence electrons. It is derived that the surface bond contraction and the rise in surface-to-volume ratio enhance the crystal field and determine the trend of frequency change, while oxidation enhances this behaviour by adding a constant.