Site-selective laser-spectroscopy studies of the intrinsic 1.9-eV luminescence center in glassy SiO2

The intrinsic 1.9-eV photoluminescence band (the R band) in neutron-irradiated synthetic silica glass has been studied using site-selective photoluminescence excitation in the 2.0 eV absorption band and transient spectral hole-burning techniques. The measurements of the low-energy wing of the zero-phonon line intensity distribution function confirm the predicted nearly Gaussian shape with a peak at 1.93 eV and a half-width of 86 meV. The homogeneous shape of the emission contour (''single-site spectrum'') has been evaluated by a selective saturation method, revealing, a phonon sideband with a peak at 60 cm-1 and a width of approximately 500 cm-1. The total Huang-Rhys factor is estimated as 1.50±0.5 and the partial Huang-Rhys factor for the interaction with the 890 cm-1 local vibration is 0.08±0.04. The analysis of spectral parameters indicates that the R band cannot be due to peroxide or ozonide molecular ions and upholds the attribution of the center to the nonbridging oxygen hole center.