Correlation between structural and optical properties of Si nanocrystals embedded in SiO2: The mechanism of visible light emission

The size distribution, band gap energy, and photoluminescence of silicon na nocrystals embedded in SiO2 have been measured by direct and independent me thods. The size distribution is measured by coupling high-resolution and co nventional electron microscopy in special imaging conditions. The band gap is calculated from photoluminescence excitation measurements and agrees wit h theoretical predictions. Their correlation allows us to report the experi mental Stokes shift between absorption and emission, which is 0.26 +/-0.03 eV, independent of average size. This is almost exactly twice the energy of the Si-O vibration (0.134 eV). These results suggest that the dominant emi ssion is a fundamental transition spatially located at the Si-SiO2 interfac e with the assistance of a local Si-O vibration. (C) 2000 American Institut e of Physics. [S0003- 6951(00)02646-2].