Tl ion-exchange borosilicate glass: Investigation of the Tl site by X-ray absorption spectroscopy

We present a first experimental investigation on the Tl site in Tl-doped borosilicate glass by Tl/Na ion-exchange process. The local order around Tl was investigated by the EXAFS spectroscopy on a set of different samples, obtained by varying the composition of the molten salt bath (TlNO3/NaNO3 molar ratio from 0.001 to 0.4) and the bath temperature (between 350 degrees C and 380 degrees C). We show that after a 1 h exchange, Tl is surrounded by O atoms in the first shell and that the Tl-O distance is sensibly shorter than both the Tl-O distance found in Tl oxides and the typical Na-O distance in a glass. When the exchange process is extended to 1 week, the measured Tl-O distance increases towards the values found in crystalline Tl oxides, suggesting a stress release during longer exchange duration. (C) 2007 Elsevier B.V. All rights reserved.