Vidros e Vitrocerâmicas Luminescentes de Germanato de Tântalo

Abstract

New stable, homogeneous and transparent glasses were obtained from glass former GeO2 with incorporated Ta2O5 in concentrations up to 20%, with the addition of M2O alkali oxides; M = Li, Na, K, Rb, Cs for evaluation of the modifier´s influence in the glass formation of the ternary system. The different alkali oxides where compared to evaluate their relative efficiency and the first compositions were melted in platinum crucible in high temperature oven and quenched. The potassium containing glass-ceramics were prepared by annealing in oven, with nucleation time of 10 h at 770 ºC and growth at 830 ºC for 20, 40, 60 and 100 h. Sodium based glass-ceramics were obtained after annealed at 724 ºC for 2 h for nucleation and growth at 734 ºC for 25 h. Structural investigations were performed by FTIR, Raman, XRD and thermal analysis (DSC). The glass-ceramics contain the crystal phase Na2Ta8O21 or an analogous phase of K2Ta8O21. Calculation and high-resolution transmission electron microscopy confirmed the nanoscale of these formed phases. Optical characterization were performed by UV-Vis-NIR spectroscopy to obtain the transmission window for prepared samples. Glasses doped with optically active ions (Eu3+, Er3+ e Tm3+) and co-doped Er3+/Yb3+, Tm3+/Yb3+ e Er3+/Tm3+/Yb3+ glasses were prepared. Eu3+ was used as a probe, showing a shift from CS to C2v symmetry sites. The investigated luminescent properties clearly showed the tantalum influence in the glasses and glass-ceramics visible and infrared emission, such as doubling the bandwidth around 1550 nm (from 42 nm to 87 nm). The cross-section and optical gain were calculated, showing potential for optical amplification. Up-conversion phenomena from IR to visible was observed and characterized. The Judd-Ofelt parameters were determined for the Eu3+ and Er3+ for different matrices.