Influence of La/Al ratio on the structure and spectroscopy of Tm3+ doped Al2O3-La2O3-SiO2 glasses

Lanthanum aluminosilicate (LAS) glasses with compositions (Tm2O3)(0.8)-(Al2O3)(12-x) (La2O3)(x)-(SiO2)(87.2) (x = 0, 1.2, 4.5 mol%; La/Al = 0, 1/9, 3/5) were prepared via a sol-gel method combined with high temperature sintering. The total amount of Al2O3 and La2O3 was 12 mol%. The effect of the La/Al ratio on the structure and spectroscopic properties of Tm3+ has been studied in detail. The structure of Tm-3+ doped LAS glasses was studied via Al-27 nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The spinning sideband patterns of the Al-27 NMR spectra showed that the population of Tm3+ ions in the vicinity of Al3+ decreased with an increase in the La2O3 concentration. FTIR and Raman spectra suggest that glasses with high La/Al ratios have less interconnected glass networks. The spectroscopic properties of Tm3+ ions were investigated via the Judd-Ofelt method using the measurement of absorption and emission spectra. Both the 1.8 mu m fluorescence intensity and the relative intensity of up-conversion emission of Tm3+ ions decrease with an increase in the La/Al ratio. This indicates reduced cross relaxation between Tm3+ ions in glass with a high La/Al ratio. We conclude that the spatial distribution homogeneity of Tm3+ ions in LAS glass improves when the La/Al ratio increases. (C) 2016 Elsevier B.V. All rights reserved.