Effects of heat treatment on absorption bands in OH-free and OH-containing fused quartz

Abstract

Effects of heat treatment on absorption bands in fused quartz produced by melting natural quartz powder containing 2ϫ10 17 cm Ϫ3 ͑sample I͒ and 1.3ϫ10 19 cm Ϫ3 of OH ͑sample II͒ were studied. Both samples have an absorption peak at Ϸ5.2 eV. Fluorescent spectra and the results of Gaussian peak decomposition suggest that this absorption is associated with the B 2 ␤ band with a peak at 5.15 eV and full width at half maximum of 0.42 eV. The 5.15 eV band and an absorption component at 7.5 eV in sample II were annealed out at 1423 K, whereas almost no change was observed in the absorption spectra of sample I. The decrement of the 5.15 and 7.5 eV bands was proportional to the decrement of the OH content. The annealing mechanism in sample II can be explained using a previously proposed model for OH-containing fused quartz wherein the B 2 ␤ band is the twofold-oxygen-coordinated silicon ͑ϭSi:͒ coordinated with two ϵSi-OH structures. Sample I must have a ϭSi: structure, but it may not be annealed out because it does not have sufficient OH to form the twofold-coordinated ϵSi-OH on ϭSi:. The origin of the other absorption bands was also discussed.

Structural change of OH-free fused quartz tube by blowing with hydrogen–oxygen flame

“…FQ has an absorption band near 5 eV called the B 2 band. FQ used in the present study is of a similar type to that used previously [6], i.e., FQ produced by melting in an electric furnace. The only difference is that the present tube is formed directly after melting the raw material.…”

“…In the previous investigations, we studied the characteristics of the UV absorption bands in FQ [5,6]. FQ has an absorption band near 5 eV called the B 2 band.…”

“…A number of models for the origin of the B 2 b band has been proposed: [4] ODC(II), twofold-oxygen-coordinated silicon [TOCS(@Si:)], and Ge-related oxygen vacancies such as BGeÁ Á ÁSiB. We assumed, in previous papers [5,6], that the origin of B 2 b is TOCS. During the blowing process, H 2 O and H 2 molecules must react with ODC or TOCS as Utilizing these reactions, B 2 bands near the OSS must be bleached.…”

“…The properties of the B 2 b band are affected by its surroundings. For example, the B 2 b band in type-II FQ can be annealed out in atmospheric ambient while that in type-I FQ cannot [6]. In a previous paper [6], we proposed a model based on the assumption that the B 2 b band is caused by twofoldoxygen-coordinated silicon [TOCS(@Si:)].…”

“…For example, the B 2 b band in type-II FQ can be annealed out in atmospheric ambient while that in type-I FQ cannot [6]. In a previous paper [6], we proposed a model based on the assumption that the B 2 b band is caused by twofoldoxygen-coordinated silicon [TOCS(@Si:)]. The difference in the annealing properties of the B 2 b bands in type-I and type-II FQ could be derived from the effect of BSiAOH which coordinates with the TOCS [6]; the B 2 b band in type-II FQ is coordinated by two BSiAOH's, while that in type-I FQ has no such coordinated BSiAOH.…”