Materials Science and Engineering B 149 (2008) 171–176 Site of transition metal ions in ion-exchanged metal-doped glasses C. Maurizio a,∗ , F. D’Acapito a , C. Sada b , E. Cattaruzza c , F. Gonella c , G. Battaglin c a CNR-INFM-OGG c/o European Synchrotron Radiation Facility, 6 rue J. Horowitz, BP 220 38043 Grenoble, France b Physics Department, University of Padova, via Marzolo 8, 35131 Padova, Italy c Chemical Physics Department, University Ca’ Foscari of Venezia, Dorsoduro 2137, 30123 Venezia, Italy Received 12 October 2007; accepted 19 November 2007 Abstract Metal-for-alkali ion-exchange is largely used to dope surface layer of glass with metal ions so inducing a modification of the optical properties of the doped layer, useful to fabricate low-loss optical waveguides. X-ray absorption spectroscopy is a particularly important technique used to investigate the site of the metal ions introduced into the matrix, in specific cases also singling out the dopant oxidation state. Two case studies are reported in this paper, namely Cu-for-Na and Ag-for-Na ion-exchange layers of silicate glasses. The experimental results show that the site of the dopant ion is different from the one that replaced alkali ion: while in the first case the Cu site (i.e. the first oxygen shell around the metal species) is a linear combination of the sites of the crystalline oxides (CuO or Cu 2 O), with linear combination coefficients that depend on the average oxidation state, in the case of Ag, the Ag–O distance is much longer than in the Ag 2 O. Moreover, it comes to depend critically on the dopant concentration and on the subsequent heating treatments, indicating a higher stability of the Ag sites that exhibit a shorter Ag–O distance. © 2007 Elsevier B.V. All rights reserved. Keywords: Ion-exchange; Metal-doped glasses; X-ray absorption spectroscopy 1. Introduction Metal-for-alkali ion-exchange is largely used to dope surface layers of glass with metal ions. This process usually consists in substituting alkali ions in a glass matrix by other ions coming from a molten salt bath into which the glass is immersed [1]. The interest in the realization of such materials is at least two- fold. First, the exchanged ions, which have a higher electronic polarizability and/or a larger ionic radius, locally increase the refractive index of the matrix. If the dopant atoms remain disper- sed into the matrix, low-loss optical channel waveguides may be thus realized by exchanging ions through the window openings of a mask deposited onto the glass surface. To this respect ion- exchange on glass technologies dedicated to integrated optics applications have proved their advantages for designing optical circuits, presenting a good compatibility with the fiber techno- logy as well as low losses [1,2]. On the other hand, it has been shown that the clusterization of the dopant in nanometric aggre- gates can be promoted by laser or light ions irradiation [3,4]. The interest in this kind of composite systems that contain clus- ∗ Corresponding author. Tel.: +33 4 76882530; fax: +33 4 76882974. E-mail address: maurizio@esrf.fr (C. Maurizio). ters is due to their non-linear optical properties; moreover, it has been recently demonstrated that sub-nanometric metal clusters in an Er-doped silica matrix may act as sensitizers, giving rise to a significant increase of the 1.54 m emission efficiency of the Er ions, with potential application in the optical communication technology [5]. A metal-doped layer in which the aggregate size is less than 1 nm is still expected to efficiently guide the light, so that optical active waveguides can be realized. Since the aggregation state of the dopant determines the opti- cal properties of the ion-exchanged glass, it is crucial to use a characterization technique that can measure the site of the dopant atoms in the matrix. X-ray absorption spectroscopy, performed at the K or L III photoelectric absorption edge of the dopant ato- mic species, gives unique information on the short-range order around the metal site in terms of number and kind of atoms that surround the dopant atoms, their distance from the absorber and the structural disorder of the first coordination shells [3,6–10]. In this paper, we will focus on two case studies on the site of transition metal ions in ion-exchanged waveguides, where most part of the dopant atoms are dispersed into the matrix and oxidized. In literature different investigations on the local order around dopant in ion-exchanged glasses are found ([11,12] and Refs. therein); they focus mainly on Ag-for-Na ion-exchanged glasses for which the ion-exchange process (in a wide range of 0921-5107/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2007.11.015