Síntese e caracterização de vidros no sistema KPO3-Ta2O5.

Abstract

In this work new compositions of tantalum phosphate glasses were synthesized and their thermal and structural properties characterized for possible optical applications. Glasses were prepared by the classical melt-quenching method. For constant tantalum oxide contents, phosphate glasses with different alkali metals (Na, K, Rb) were synthesized, and potassium was chosen for the continuity of the work due to more suitable synthesis conditions. Thus, glasses were prepared in the binary system KPO3-Ta2O5, with a molar concentration of Ta2O5 varying from 10 to 40%. Thermal analyzes allowed to determine the characteristic temperatures of the samples and to note that glass transition temperatures increased with the increase of Ta2O5 content, indicating that the insertion of Ta in the network, as an intermediate, increases the connectivity. Spectroscopic studies by FTIR and Raman showed a structural modification of the glasses with Ta2O5addition, also suggesting the insertion of Ta in the phosphate network and formation of P-O-Ta bonds. Spectroscopic analyzes in the ultraviolet, visible and infrared regions allowed to determine the transparency window of these glasses, as well as band gap energies. In the infrared region there was an increase in the transparency of glasses, suggesting a decrease in phonon energy for higher Ta2O5 contents. The decrease in the band gap values with increasing Ta2O5 contents evidences that the insertion of Ta in the phosphate network increases the number of molecular orbitals of the valence and conduction bands of the material. Ellipsometry measurements allowed to observe an increase in the refractive index of the glasses with the addition of Ta2O5, (n~2 for glass with 40% of Ta2O5), also indicating the insertion of Ta in the network. Glasses in the KPO3-Ta2O5 system were doped with 0.3%mol of europium ions and analyzed by luminescence, which provides informations of the sites occupied by rare earth ions. It was observed that by increasing Ta2O5 content, there was a decrease in the symmetry of the sites occupied by Eu3+ and that the emission quantum efficiency increases, also indicating the decrease of the glass phonon energy with the insertion of Ta and favoring radiative emissions of ions rare earths in this vitreous matrix.