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-ir radiated synthetic silica glass has been studied using site-selective photoluminescence excitation in the 2.0 eV absorption band and transie nt spectral hole-burning techniques. The measurements of the low-energ y 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 (''sin gle-site spectrum'') has been evaluated by a selective saturation meth od, 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 peroxid e or ozonide molecular ions and upholds the attribution of the center to the nonbridging oxygen hole center.