Use of optically detected magnetic resonance to correlate germaniumelectron centres with UV absorption bands in x-ray irradiated germanosilicateglasses

Abstract

The relationship between paramagnetic defect centres and UV absorption bandssimultaneously generated by ionizing radiation in Ge-doped SiO2 glass isinvestigated using magneto-optical techniques. A sample of 7.0 mol% Ge-dopedSiO2 was exposed to x-ray radiation, which resulted in the formation ofabsorption bands centred at 4.4 eV and 5.7 eV as well as electron spinresonance (ESR) signals attributed to the Ge(1) and Ge(2) defects. To isolateparamagnetic contributions to the induced optical absorption, the magneticcircular dichroism absorption (MCDA) spectrum was measured at severaldifferent temperatures over the range 2.00-6.21 eV. The optically detectedmagnetic resonance (ODMR) spectrum was then obtained at 4.42 eV viamicrowave-induced changes in the MCDA signals in order to unambiguouslycorrelate this optical transition with a particular ESR signal. The ODMR dataindicate that the Ge(1) centre is responsible for this absorption band,providing the first unequivocal correlation of ESR and optical properties forthis defect. In addition, evidence of a weakly absorbing paramagnetic defect,that appears to be related to the Ge(2) centre, was found at 5.65 eV.