Aluminum effects on structure and spectroscopic properties of holmium-doped sol-gel silica glasses

A series of Ho3+-doped silica glasses containing different Al2O3/Ho2O3 mole ratios were prepared successfully using a sol-gel method combined with high temperature sintering. The X-ray diffraction (XRD), nuclear magnetic resonance (NMR) spectra of Al-27, and X-ray photoelectron spectra (XPS) of O1s, as well as the absorption and fluorescence spectra of the Ho3+ ions in these silica glasses, were recorded and analyzed systematically. The Al-27-NMR spectral studies indicated that Al3+ ions entered the glass structure mainly in sixfold and fivefold co-ordination for the series of solegel HAS glasses with constant 0.2 mol% Ho2O3 content. The NMR and XPS results obtained indicated a relationship between the amounts of Al2O3 and Ho2O3 and the Al coordination. Based on the structure and spectroscopic properties of the Ho3+-doped silica glasses, it was concluded that the optimum Al2O3/Ho2O3 mole ratio for the Ho3+/Al3+ co-doped silica glass for a 2-mu m laser was 15. (C) 2015 Elsevier B.V. All rights reserved.