The optical absorption and luminescence bands near 2 eV in irradiated and drawn synthetic silica

Abstract

The annealing behaviors of the 2 eV optical absorption and luminescence and of the various paramagnetic defect centers (E′, O 2 − and nonbridging oxygen hole center [HBOHC]) in irradiated synthetic silica rods and unirradiated drawn fibers have been measured. Good agreement was found between the intensities of the 2 eV absorption and luminescence bands and the sum of the intensities of the hole traps in irradiated Suprasil W, suggesting that the optical transitions in this low OH material might be due to a nonparamagnetic electron trap. However, in Suprasil equally good correlations were observed between the absorption and luminescence and the NBOHC intensity for anneal temperatures above 100°C, consistent with the postulate that the 2 eV bands in high OH silica are principally due to the NBOHC. Although the ESR spectrum attributable to NBOHCs was observed for the first time in as-drawn low OH silica fibers, preliminary estimates of oscillator strength support the suggestion that the drawing-induced 2 eV absorption is nonetheless due to the nonparamagnetic electron trap.