  Photoluminescence (PL) and Raman spectra of sol-gel-derived silica glasses
were studied in course of the consolidation of xerogel to dense glass. A number
of ultraviolet PL bands in 3 eV - 4 eV region were found, which have not been
observed in pure silica glasses not exposed to carbon compounds. Such PL bands,
some of which exhibit distinct vibronic structures at room temperature, have
been persistently reported in various high-surface porous or nanoparticle forms
of SiO2. Based on their spectral shapes and decay kinetics properties, the
structured PL bands in the 3.7-3.8 eV and 3.1-3.3 eV regions are assigned to
polycyclic hydrocarbons, naphthalene and pyrene, respectively, which are formed
from ethanol molecules created by hydrolysis of tetraethoxysilane. These data
support the hypothesis that PL activity of carbon-doped silica may be related
to embedded aromatic carbon groups.
