LOCAL-STRUCTURE AROUND ER IN SILICA AND SODIUM-SILICATE GLASSES

Extended X-ray absorption fine structure (EXAFS) and Photoluminescence (PL) measurements have been performed on three different Er-doped glasses: silica and sodium silicate doped with Er in the Molten phase, and silica doped by MeV ion implantation. All samples show a luminescent transition centered around a wavelength of lambda = 154-mu-m, corresponding to an intra-4f transition of Er3+. EXAFS data show that the Er ions have about six O first neighbors, at a distance of 2.26 angstrom in all systems. Both silica glasses show a second-neighbor Er-Si shell at 3.11 angstrom which is not seen in the sodium silicate glass. This difference is reflected in a difference in the PL spectra. The Er-O shell in the silica g]ass Shows 0.01 angstrom 2 more disorder than that in the Na-loaded material. These findings are rationalized in terms of the network-modifying effect of Na. Both EXAFS and PL show no significant differences between silica samples prepared in the molten phase or by implantation. At an Er concentration of approximately 1 at.%, no direct Er-Er bonds are observed.