Influence of earth-alkali fluorides (MgF2, CaF2, SrF2, BaF2) and Nb2O5 on the structural and optical properties of fluorophosphoniobate glasses

Abstract

The main objective of the project is the study of fluorophosphoniobate glasses obtained from sodium metaphosphate (NaPO3) combined with earth-alkali metal fluorides XF2 (X = Mg, Ca, Sr, Ba) and Nb2O5. Glasses with molar composition (80-y)NaPO3-(20)XF2 -(y) Nb2O5 will be obtained by the melt-cooling method and characterized as to their structural, optical, luminescent and thermal properties as a function of the concentration of Nb2O5 and X in XF2. Based on preliminary results obtained in the FAPESP Scientific Initiation project, in which the change in the oxidation state of niobium as a function of earth-alkali metal fluorides was demonstrated, this master's project proposes the systematic study of the formation of Nb4+ and Nb5+ species in function of synthesis parameters and fluoride precursors, and characterized by x-ray photoinduced spectroscopy (XPS) and x-ray absorption near edge structure (XANES) (Sirius). In view of the periodic change in the atomic radius from Mg to Ba, the structural, thermal, optical and luminescent properties will be systematically studied as a function of X and Nb2O5 concentration. Such properties will be explored by solid state nuclear magnetic resonance (NMR) (31P, 23Na, 93Nb), Raman and differential scanning calorimetry (DSC). In order to obtain data on the structure of the glass punctually, since the matrix is promising for obtaining optical glasses, the matrices will be doped with Sc3+, Eu3+ and Yb3+, which will be used as structural probes for measurements of NMR, luminescence and electron paramagnetic resonance (EPR), respectively, providing important information regarding the local environment of these rare earth ions in the glass matrix.