TY: JOUR T1 - Structural and optical properties on thulium-doped LHPG-grown Ta2O5 fibres A1 - Macatrão, M. A1 - Peres, M. A1 - Rubinger, C. P. L. A1 - Soares, M. J. A1 - Costa, L. C. A1 - Costa, F. M. A1 - Monteiro, T. A1 - Franco, N. A1 - Alves, E. A1 - Saggioro, B. Z. A1 - Andreeta, M. R. B. A1 - Hernandes, A. C. N2 - Structural, spectroscopic and dielectric properties of thulium-doped laser-heated pedestal Ta2O5 as-grown fibres were studied. Undoped samples grow preferentially with a single crystalline monoclinic structure. The fibre with the lowest thulium content (0.1 at%) also shows predominantly a monoclinic phase and no intra-4f12 Tm3+ recombination was observed. For sample with the highest thulium amount (1.0 at%), the appearance of a dominant triclinic phase as well as intraionic optical activation was observed. The dependence of photoluminescence on excitation energy allows identification of different site locations of Tm3+ ions in the lattice. The absence of recombination between the first and the ground-state multiplets as well as the temperature dependence of the observed transitions was justified by an efficient energy transfer between the Tm3+ ions. Microwave dielectric properties were investigated using the small perturbation theory. At a frequency of 5 GHz, the undoped material exhibits a dielectric permittivity of 21 and for thulium-doped Ta2O5 samples it decreases to 18 for the highest doping concentration. Nevertheless, the dielectric losses maintain a very low value. UR - https://ria.ua.pt/handle/10773/6114 Y1 - 2009 PB - Elsevier