Estudos de vidros fluoroboratos e fluorogermanatos de chumbo, através de técnicas de espectroscopia óptica e de ressonância magnética

Abstract

In this work two studies on rare earth−doped (Eu3+, Yb3+) lead fluorogermanate (GeO2−PbO−PbF2) and fluoroborate glasses (B2O3 −PbO −PbF2) were investigated. The main advantages of these glasses are their chemical stability and low phonon energy compared to many oxide-based glasses which make these materials excellent candidates for applications in optical, electronic, and laser devices. The UV/Vis absorption and photoluminescence techniques were used for obtaining optical information while Electron paramagnetic resonance (EPR) (continuous wave and pulsed), Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) and Raman techniques were used to obtain structural information of these glasses. In the first study GeO2−PbO−PbF2 and B2O3−PbO−PbF2 composition glasses in which PbF2 was increased and Al2O3 was added for the purpose of knowing the effect of these reagents on the optical parameters and the structure. The optical studies suggested the presence of Al2O3 and PbF2 can generate positive effects on the optical properties for instance, their addition increased the lifetime and decreased the alpha factor which are parameters related to the quantum efficiency and non-radiative processes in these glasses. Magnetic resonance techniques provided information about changes on the structure such as the presence of 10B, 11B and 27Al atoms in the second coordination sphere of the rare earth for borate glasses and absence of 207Pb and 19F atoms and incorporation of 27Al in this second sphere as a result of Al2O3 addition in germanate glasses. As result of increasing the PbF2 and Al2O3 the ratio BIII/ BIV increases, more Al-F bonds are formed and shift of the main F peaks were observed. These results suggest a strong influence of the change of the structure on the optical properties of these glasses. In the second study oxyfluoride glasses of the compositions (40−x)B2O3 − xGeO2 −10Al2O3 −40PbO −10PbF2 where x = 5, 10, 20, 30, 35 were prepared to gain the benefits of both compositions matrix, replacing the expensive GeO2 component by B2O3. The idea was to obtain glasses with good optical properties and low cost. The addition of Al2O3 is expected to produce local field variations around rare ions and such changes may have strong bearing on luminescent transitions of these ions. The optical results show that substitution of GeO2 by B2O3 reveals the close relationship between the quantum efficiency of the rare earth and decreasing of the non-radiative processes. The results of magnetic resonance confirm the presence of 11B, 10B and 207Pb in the second coordination sphere of rare earth. The relative concentrations of BIII , BIV , AlIV , AlV , and AlVI have a progressive response with the substitution of GeO2 by B2O3. This is an important result because shows the possible correlation between the structure and the optical properties, reinforcing the hypothesis of the crucial role of the structure for achieving the desired optical properties. Finally, the results obtained in this work suggest the possibility of fabricating glasses with good optical properties, mixing the properties of both glasses, borate and germanate and being more economically priced.