Clustering of germanium atoms in silica glass responsible for the 3.1 eV emission band studied by optical absorption and X-ray absorption fine structure analysis

Correlation between the 3.1 eV emission band and local atomic configuration was systematically examined for Ge+ implanted silica glass by UV–vis optical absorption spectroscopy and X-ray absorption fine structure (XAFS) analysis. The 2.7 eV emission band, commonly observed in defective silica, was replaced by the sharp and intense 3.1 eV emission band for the Ge+ fluence > 2 × 1016 cm−2, in which UV–vis absorption spectra suggested clustering of Ge atoms with the size ∼1 nm. XAFS spectroscopy indicated that the Ge atoms were under coordinated with oxygen atoms nearly at a neutral valence state on average. The present results are consistent with the previous ESR study but imply that the small Ge clusters rather than the O=Ge: complexes (point defects) are responsible for the 3.1 eV emission band.