Defects In Silica Glass Research Articles

Optical Properties and Structure of Defects in Silica Glass

This paper reviews what is known about the structures and optical properties of point defects in silica glass and other amorphous forms of SiO2. The available structural information derives mainly from the results of electron spin resonance (ESR) spectrometry-a method which is directly applicable only to the subclass of defects which are paramagnetic. The intrinsic paramagnetic centers so far identified by ESR include E' centers (≡Si·), nonbridging-oxygen hole centers (≡Si-O·), peroxy radicals (≡Si-O-O·), and self-trapped holes. Examples of intrinsic diamagnetic defects believed to occur in silica in include neutral oxygen vacancies (≡Si-Si≡), two-coordinated silicone (O-Si-O-), and peroxy linkages (≡Si-O-O-Si≡). The most common extrinsic defects are associated with hydroxyl and chloride impurities. Radiolytically induced H0 and H2 play important roles in the post-irradiation growth and decay kinetics of defects in glasses containing_??_100ppm OH. A compendium of ESR/optical correlations taken from the literature points to the most likely origins of many defect-related optical absorption bands in the visible, ultraviolet and vacuumultraviolet spectral regions. Others of these bands have been ascribed to interstitial O2, O3 and Cl2 molecules on the basis of similarities of their spectral positions and widths to those of the corresponding species in the gas phase.

Stree-induced photoluminescene in pure silica optical fibers

Changes in photoluminescence (PL) originating from non-bridging oxygen hole centers (NBOHCs) are investigated by applying tensile stress up to 4GPa to silica optical fibers. The formation of NBOHCs, that is, SiO bond breakage, is related to the formation of valence alternative (VA) defects in silica glass. The PL intensity increases with increasing applied stress and almost reverts to the initial state on release of the stress. The concentration of NBOHCs induced by a stress of 4 GPa is, however, very low (about 10 14 spin/g). Thus, it is found the first time that applied stress causes the SiO bond breakage, which is the first step for the formation of VA defects. Moreover, the reversible change in PL intensity indicates that dangling bonds cannot be converted easily to VA defects in silica glass.