shown that only in silicate glass samples Fe3+ ... and analysed total Fe content for all doped Duran samples melted under oxidising conditions provides a specific absorption coefficient ... performance density to 10 W/m2 , pulse length -30 ns,.
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Pmc. Int. Congr. Glass, Volume 1. Invited Papers, Edinburgh, Scotland, 1-6 July 2001, 84-93
Redox equilibria and ultraviolet radiation induced defects in glasses D. Ehrt} P. Ebeling, U. Natura Otto-Schott-Institut, Friedrich Schiller University of Jena, Fraunhoferstr. 6, D-07743 Jena, Germany
U. Kolberg
K. Naumann & S. Ritter
Schott Glas Mainz, Hattenbergstr. 10, D-55014 Mainz,
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The redox equilibria of Fe ZFe and Sn ZSn in the ppm range were investigated in high purity fluoride, phos phate and borosilicate glass samples with high transmis sion in the deep ultraviolet region. The absorption bands and coefficients for the electronic transitions ofF e , Fe , Sn and Sn species were determined in the ultraviolet and vacuum ultraviolet range. The Fe ZFe ratio could be varied between 99Zl and 1/99 in fluoride, 99/1 and 1OZ 90 in phosphate and 90ZlO and 15/85 in borosiUcate glass samples by melting under oxidising or reducing conditions. The charge transfer bands of Fe and Fe species are dependent from the glass matrix. The Sn ZSn ratio could be completely shifted to the Sn only in fluoride samples. It was varied in a wide range in phosphate and the Sn content was always low, p tran sitions for Sn were detected by optical absorption and luminescence spectroscopy shifted to longer wavelength in the range fluoride—>phosphate—>silicateglass samples. Sn absorption bands were found at shorter wavelength in the vacuum ultraviolet region in all cases investigated. The influence of Fe and Fe ions on ultraviolet lamp and laser radiation induced defects was studied. Photooxidation OfFe to (Fe J was found in all glasses in vestigated. The kinetics were measured and simulated depending on the glass matrix. The experiments have shown that only in silicate glass samples Fe ions partici pate in radiation induced processes forming (Fe )' de fects which decrease the Fe absorption with the maximum at 222 nm but increase the defect absorption with the maximum at 280 nm. The defect generation in the ultraviolet region increases drastically with increas ing Fe content in the range 10-200ppm. The mechanisms are very complicated in silicate glasses with maxima and minima in the defect formation curves. In contrast to sili cate glasses Fe ions do not participate in the radiation inducedprocesses in fluoride and phosphate glasses. They are very stable against ultraviolet radiation. Sn ions in +
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silicate glasses are photo-oxidised under ultraviolet ra diation very fast which leads to an decrease of absorption near 206 nm and to an increase near 250 nm. Both Sn and Sn are involved in the radiation induced processes. 2+
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The role of glasses as ultraviolet transmitting materi als for special applications has increased in recent years. Fluoride single crystals, mainly CaF , and high purity vitreous silica are well known materials used for deep ultraviolet optics, especially in microlithography. Moreover, for the various applications, a variety of glasses with different properties is required. Fluoroaluminate and phosphate glasses with high purity are also good ultraviolet transmitting materials " ' with a large intrinsic band gap. It was found that a traditionally old borosilicate glass type Duran similar to Borofloatmelted with start ing materials of special high purity has also a high transmission in the deep ultraviolet range.' " ' Its struc ture and properties are mainly determined by the M O/ B O ratio, the so-called boric oxide anomaly' ' so it has almost entirely bridging oxygens e.g. a very low optical basicity (Λp absorption bands due to trace impurities of metal ions, such as Fe IVe , Pb , etc., which are influenced by the glass matrix. * · ~ ' It was shown that both intrinsic and extrinsic absorption are important for ultraviolet radiation induced defects in the glasses.' " · · · ' The aim of this paper is the investigation of the charge transfer absorption of F e and Fe^ , the s-»p absorption of Sn and the d->s ab sorption of Sn and their role in ultraviolet lamp and laser radiation induced defects in Duran glass samples of special high purity, in comparison with fluoroaluminate and phosphate samples. Trace amounts of tin are introduced through the float bath during the Borofloat process.' ' Iron is an unavoidable trace impu rity in all multicomponent glasses produced by the melt ing technique mainly introduced with the raw materials. Photo-oxidation of F e induced by ultraviolet radia tion was found in silicate, fluoride and phosphate glasses 2
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