International audienceAbstract—Experimental characterization through electron paramagnetic resonance (EPR) and confocal luminescence microscopy (CML) of a Ge-doped glass (preform and fiber) reveals the generation of several point defects by 10 keV X-ray radiation-induced attenuation: GeE', Ge(1), Ge(2), and Ge-ODC. The generation mechanisms of Ge-ODC and charged defects like GeE' centers are studied through ab initio simulation. Our calculations used a 108 atom supercell with a glass composition comparable to the Ge-doped core or to the pure-silica cladding of the canonical sample. The large size of our cell allows us to study the influence of the local environment surrounding the X-ODC defect (X = Si or Ge) on its structure parameters (e.g., Si-X bond length) and its energy of formation. We found a statistical correlation between these two characteristics for pure- and Ge-doped silica-based glasses suggesting that the Si-ODC and Ge-ODC will be preferentially generated at sites leading to the shortest Si-X distances. We also evaluated the possible influence of the local environments of the defect on their generation mechanisms. From the whole set of possible X-ODC in the amorphous cells, we calculated the charged structures that can be obtained through the removing of one electron of the cell. For pure-silica glass, about 80% of the oxygen vacancies lead to a dimer structure and 20% to puckered ones. For the doped glass, the percentage of the final dimer structures is reduced to 42% while the puckered charged percentage increases to 36%. We also note the appearance of 22% of divalent centers. Further simulation shows that the presence of the Ge inside the glass strongly affects the generation mechanisms of Si-related centers
We report an experimental study on phosphorus-related point defects in amorphous silica, based on photoluminescence, absorption, and electron spin resonance measurements carried out on P-doped SiO2 fiber preforms. By photoluminescence measurements excited by laser or synchrotron light we detect an emission band peaked at 3.0 eV with a lifetime in the range of ms. The excitation spectrum of the 3.0 eV emission consists of two transitions peaked at 4.8 and 6.4 eV, the former giving rise also to a measurable absorption band. We attribute this optical activity to a P-related point defect embedded in SiO2, based on the spatial correlation between the emission intensity and the P doping level. A detailed spectroscopical investigation allows us to propose a scheme of the electronic levels of this P-related defect, in which the 4.8 and 6.4 eV excitation channels arise from transitions from the ground to two-excited singlet states, while the long-lived 3.0 eV emission is associated to a spin-forbidden transition from an excited triplet to the ground state. Finally, electron spin resonance measurements on X-irradiated samples lead us to propose a tentative microscopic model of the defect as a diamagnetic four-coordinated P impurity substitutional to a Si atom
Nuclear magnetic resonance absorption in oriented polytetrafiuoroethylene fibers has been investigated in the temperature range 170o-380 o K. The sample, in the form of a parallel bundle of fibers, showed a marked dependence of line shape on the direction of the applied magnetic field over the temperature range studied, although the observed anisotropy was much greater above 285°K than below. Changes occurring in the linewidth and second moment at around 285°K indicate a rotational disorder transition in the crystalline regions of the polymer, and serve to illustrate the advantages of using oriented fibers in the NMR investigation of semicrystalline polymers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.