Stabilized electronic state and its luminescence at the surface of oxygen-passivated porous silicon

Photoluminescence (PL) spectra of as-made porous Si samples were obtained i n a wide peak-wavelength range. After exposure to air or coupling with C-60 molecules, the PL peak shifts to a pinning wavelength within the range of 610-630 nm. This pinning wavelength is almost independent of the size of th e original porous Si nanocrystallites and both redshifting and blueshifting can occur for different sizes. A self-consistent effective-mass calculatio n shows that the Si=O binding states are responsible for the radiation of t his pinning wavelength and the blueshift for the large nanocrystallites is due to the additional potential modulation within the Si nanocrystallite by the long-range Coulomb interaction of oxygen ions.