Showing papers by "E. J. Friebele published in 1985"

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′, O2− 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.

Overview Of Radiation Effects In Fiber Optics

Abstract: The optical properties of fiber waveguides can be degraded by exposure to nuclear radiation, primarily through the generation of color centers in the fiber core. This paper will review recent studies of the radiation-induced absorption in state-of-the-art fiber optics. Particular emphasis is placed on the development of more radiation resistant pure and doped silica core waveguides and on the understanding of the damage processes in these materials. The results of studies of radiation damage in high birefringent, polarization-maintaining fibers and in heavy metal fluoride glasses and fibers will also be reviewed.

Radiation effects in ZrF4 based glasses: II. Optical absorption

Abstract: The optical absorption spectra of ZrF 4 -based glasses such as ZB, ZB+Ce, and ZBLAL X-irradiated at 80 K have been resolved into component bands at 2.68, 4.27 and 5.00 eV. Studies of the annealing behaviors of the optical bands and defect centers elucidated by ESR have correlated the 2.68 eV band with Zr 3+ and the 4.27 eV band with trapped hole centers such as the V K , V H , and possibly V KA . Addition of PbF 2 to the base glass results in a reduction in the 2.68 eV band intensity and the appearance of bands attributed to Pb 3+ and Pb + , indicating that the Pb 2+ in the unirradiated glass is an amphoteric trap for both radiolytic holes and electrons.

Nitrogen-associated paramagnetic defect centers in sputtered SiO2 films

Abstract: Electron spin resonance studies of SiO 2 films prepared by rf sputtering have revealed the presence of defects intrinsic to the silica network, such as the E′ center and peroxy radical. Films sputtered in a mixed ArN 2 atmosphere were found to contain bridging nitrogen centers; the spectroscopic parameters are consistent with SiNSi structures. A low concentration of NO 2 molecules has been identified in a second series of films deposited in Ar with resputtering. Although the molecules are immobilized in the silica network, they undergo thermally-activated librational motion.

EPR spectra of gel-to-glass reactions

Abstract: Simple SiO 2 gels have been annealed to temperatures ranging from 100°C to 700°C and then irradiated with X-rays. The resulting electron paramagnetic resonance spectra contain a rich variety of the features associated with organic radicals and with glasses. By examining the spectra for different anneal temperatures, we are able to follow the transformation from gel to glass. The amount of peroxy bonding seems to be significantly greater than that observed in glasses produced from high temperature melts, pointing to a newly discovered intermediate stage in the process of forming glass from a gel.