  The relationship between paramagnetic defect centers and UV absorption bands
simultaneously generated by ionizing radiation in Ge-doped SiO2 glass is
investigated using magneto-optical techniques. A sample of 7.0 mol% Ge-doped
SiO2 was exposed to X-ray radiation, which resulted in the formation of
absorption bands centered at 4.4 eV and 5.7 eV as well as electron spin
resonance (ESR) signals attributed to the Ge(1) and Ge(2) defects. To isolate
paramagnetic contributions to the induced optical absorption, the magnetic
circular dichroism absorption (MCDA) spectrum was measured at several different
temperatures over the range 2.00-6.21 eV. The optically detected magnetic
resonance (ODMR) spectrum was then obtained at 4.42 eV via microwave-induced
changes in the MCDA signals in order to unambiguously correlate this optical
transition with a particular ESR signal. The ODMR data indicates that the Ge(1)
center is responsible for this absorption band, providing the first unequivocal
correlation of ESR and optical properties for this defect. In addition,
evidence of a weakly absorbing paramagnetic defect was found at 5.65 eV that
appears to be related to the Ge(2) center.
