UV-absorption and radiation effects in different glasses doped with iron and tin in the ppm range - 04/04/08
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Abstract |
Intrinsic and extrinsic ultraviolet absorption and radiation-induced effects were investigated in different glass types, fluorides, phosphates and borosilicates. High-purity glass samples were prepared and their intrinsic absorption was measured in the vacuum ultraviolet region. The influence of doped iron and tin species in the ppm range on the ultraviolet absorption and radiation-induced effects were studied. The maximum of the dominating Fe3+ charge transfer band has the lowest energy (4.8 eV) and intensity in the fluoride glass and the highest energy (5.6 eV) and intensity in the borosilicate glass samples. The charge-transfer band for Fe2+ has much lower intensity and higher energy (5.7 eV) than those for Fe3+ in all glasses investigated. Photo-oxidation of Fe2+ to (Fe2+)+ hole centres and glass-matrix-related electron centres by UV irradiation increases the UV absorption drastically in all glasses. The kinetics was measured and simulated depending on the glass matrix. In fluoride and phosphate glasses, Fe3+ complexes are very stable against UV irradiation and do not participate in UV-radiation-induced processes. Only in silicate glasses, Fe3+ is able to form a (Fe3+)- electron centre defect which decreases the charge transfer absorption of Fe3+ near 220 nm, but increase the absorption of hole centre defects, with a maximum at 280 nm. So, the defect generation in the ultraviolet region increases drastically with increasing Fe content in the range 10-200 ppm. Three or four electronic s → p transitions for Sn2+ were detected by optical absorption and luminescence spectroscopy shifted to longer wavelength in the range fluoride → phosphate → silicate glass samples. Sn4+ absorption bands were found at shorter wavelength in the vacuum ultraviolet region in all cases investigated. Sn2+ ions are photo-oxidised under UV radiation very fast, which leads to an decrease of absorption near 200 nm and to an increase near 250 nm. Both Sn2+ and Sn4+ are involved in the radiation-induced processes. In contrast to phosphate and silicate glasses, tin-doped fluoride glasses are very resistant against UV lamp but not against UV laser irradiation. The mechanisms are very complicated, with maximums and minimums in the defect formation curves.
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L'absorption ultraviolette et les effets induits par l'irradiation, aussi bien de nature intrinsèque qu'extrinsèque, ont été étudiés dans différents types de verres : fluorures, phosphates et borosilicates. Des verres de haute pureté ont été préparés et caractérisés sous vide. Ces verres ont été dopés avec de l'étain et du fer.
Le texte complet de cet article est disponible en PDF.Keywords : glass, fluorides, phosphates, iron, tin, UV absorption, UV irradiation
Mots-clé : verre, fluorures, phosphates, fer, étain, absorption UV, irradiation UV
Plan
Vol 5 - N° 11
P. 679-692 - novembre 2002 Retour au numéroBienvenue sur EM-consulte, la référence des professionnels de santé.
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