Defect formation and evolution in TeO2-containing borosilicate glass films derived from a sol-gel process.

Abstract

Defects in glasses, such as the paramagnetic E' (a singly charged oxygen vacancy), the hydrogen-related doublets with different splittings, and the NBOHC's (nonbridging oxygen hole centers), are generally induced by irradiating the glasses with highly energetic photons (particles) or laser beams. We find in the present work that the paramagnetic Te E' and hydrogen-related doublets with a splitting of 1.1, 7.4, and 11.9 mT can be produced by heating the sol-gel derived ${\mathrm{SiO}}_{2\mathrm{\ensuremath{-}}}$${\mathrm{B}}_{2}$${\mathrm{O}}_{3}$-${\mathrm{TeO}}_{2}$ glass films in a hydrogen atmosphere. Optical color centers were also induced at 3.6, 4.0, and 4.2 eV, depending on the heat treatment conditions during the reducing process. On heating the reduced films in air, the paramagnetic NBOHC's occurred together with two optical absorption bands at 2.2 and 5.5 eV. The hydrogen-related defects can be clearly divided, by their different responses to the microwave power, into two groups. One includes the 1.1- and 7.4-mT doublets, which were recognized to be a variant of the Te E' center, and the other consists of the 11.9-mT doublet, which was a different defect species from the Te E' center. The Te E', 1.1-, and 7.4-mT doublets were found to be bleached more easily than the 11.9-mT doublet at a high temperature in the hydrogen atmosphere. The observed optical absorption bands at 3.6, 4.0, and 4.2 eV were tentatively attributed to some neutral oxygen vacancies on tellurium atoms in the structure, while the optical bands at 2.2 and 5.5 eV were assigned to the NBOHC's.