Influência do óxido de nióbio em vidros fosfatos contendo terras raras, obtidos pelo método de fusão, para aplicação em fotônica

Abstract

This work reports the study of two phosphate glass matrices based on phosphorus pentoxide with different amounts of niobium, these being 60P2O5.15ZnO.5Al2O3.10BaO.10PbO (mol%) + xNb2O5 0, 10, 20, 30% (wt%) (PZABP) and the 40P2O5.20Al2O3.35Na2O.5K2O(mol%) + xNb2O5 0, 10, 20, 30, 40, 50 (wt%) (PANK), both systems contain 0.3, 1.0 and 1.2% by mass of Er3+, Eu3+ and Yb3+ ions and were prepared by the fusion process. The glasses were characterized by Differential Scanning Calorimetry (CED), X-ray Diffraction (XRD), Raman scattering, UV-Vis absorption spectroscopy, photoluminescence and NMR MAS 31P, MAS 27Al, MAS 93Nb e MAS 23Na. The experiments indicate good incorporation of Nb2O5 into the glass in both systems with variation in color from transparent to blue through reduction of niobium in the PZABP matrix and transparent to light yellow in the PANK matrix.X-ray diffractometry shows alo associated with the amorphous character for both glasses. The inclusion of Nb2O5 has direct effects on the connectivity of the glass network and on the values of refractive index, optical basicity, optical electronegativity, Urbach energy and direct and indirect bandgap for the analyzed systems. The Judd-Ofelt theory is applied for spectral analysis and the matrix intensity parameters PZABP and PANK are used to estimate the spectroscopic parameters of Er3+ ions in glass such as radiative lifetime, emission probability, quantum efficiency and local environment. Under UV excitation, the emission spectra showed narrow bands attributed to Eu3+, resulting from the 5D0→7FJ transitions (J = 0, 1, 2, 3 and 4) for both phosphate systems (PZABP and PANK). Nuclear magnetic resonance (NMR) experiments for the PZABP matrix indicate an increase in the metaphosphate phase (Q2) in the 31P MAS NMR spectrum and favoring hexacoordinate coordination (NbO6) with the addition of niobium in the 93Nb MAS NMR spectrum. The 27Al MAS NMR spectra of the PZABP system indicate the presence of aluminum in four, five and six coordinations, with six-coordinate aluminum species prevailing in samples without niobium and four coordinates at their maximum concentration of 30% (mass). The 31P MAS NMR spectra for PANK glass show an increase in the pyrophosphate phase (Q1) with the addition of Nb2O5, while the 23Na MAN NMR spectra did not indicate a change in the structure around Na with its addition. In all materials studied, it was observed that the photoluminescent properties of the Eu3+ ion are only slightly modified with the amount of Nb2O5, in addition to being possible to confirm the upconversion phenomena. At least two distinct Eu3+ lifetime values are observed for each system, presenting curves with bi-exponential adjustments, suggesting a dispersion of different ionic environments within the glass structure. Excited state lifetime values ranged between 1.6 – 2.1 ms for PZABP and 0.6 – 2.2 ms for PANK sample. Co-doping with Er3+/Yb3+ promotes emission in the infrared region, with a maximum around 1535 nm and a bandwidth of 30.6 nm for PZABP and 28.3 nm for the PANK sample under 980 nm pumping. Based on the results, these glasses can be potential candidates for the construction of different devices in the area of photonics such as energy converters in the UV and near-infrared range (900 nm region) to the visible, filters for UV wavelengths and in the manufacturing of optical fibers for use in the 3rd telecommunications window.