Microwave dielectric permittivity and photoluminescence of Eu 2O3 doped laser heated pedestal growth Ta 2O5 fibers

Partilhar documento na coleção da comunidade Laboratório Associado I3NWe report the microwave dielectric properties and photoluminescence of undoped and europium oxide doped Ta2O5 fibers, grown by laser heated pedestal growth technique. The effects of Eu2O3 doping 1–3 mol % on the structural, optical, and dielectric properties were investigated. At a frequency of 5 GHz, the undoped material exhibits a dielectric permittivity of 21 and for Eu2O3 doped Ta2O5 samples it increases, reaching up to 36 for the highest doping concentration. Nevertheless, the dielectric losses maintain a very low value. For this wide band gap oxide, Eu3+ optical activation was achieved and the emission is observed up to room temperature. Thus, the transparency and high permittivity make this material promising for electronic devices and microwave applications. © 2008 American Institute of Physics.FCT-PTDC/FIS/66262/06FCT-PTDC/CTM/66195/200

Structural and optical properties on thulium-doped LHPG-grown Ta2O5 fibres

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.FCT - PTDC/CTM/66195/2006FCT - PTDC/FIS/66262/2006FCT - PTDC/FIS/72843/200

Effect of Eu2O3 doping on Ta2O5 crystal growth by the laser-heated pedestal technique

High energy band gap hosts doped with lanthanide ions are suitable for optical devices applications. To study the potential of Ta2O5 as a host compound, pure and Eu2O3-doped Ta2O5 crystal fibers were grown by the laser-heated pedestal growth technique in diameters ranging from 250 to 2600 μm and in lengths of up to 50 mm. The axial temperature gradient at the solid/liquid interface of pure Ta2O5 fibers revealed a critical diameter of 2200 μm above which the fiber cracks. X-ray diffraction measurements of the pure Ta2O5 single crystals showed a monoclinic symmetry and a growth direction of [1 1̄ 0]. An analysis of the pulling rate as a function of the fiber diameter for Eu2O3-doped Ta2O5 fibers indicated a well defined region in which constitutional supercooling is absent. Photoluminescence measurements of pure Ta2O5 crystals using excitation above the band gap (3.8 eV) were dominated by a broad unstructured green band that peaked at 500 nm. Three Eu3+-related optical centers were identified in the doped samples with nominal concentrations exceeding 1 mol%. Two of these centers were consistent with the ion in the monoclinic phase with different oxygen coordinations. The third one was visible in the presence of the triclinic phaseFCT-PTDC/FIS/66262/2006FCT-PTDC/CTM/66195/2006FAPESP and CNPq(Brazil