@PHDTHESIS{ 2024:887248752,
 	title = {Niobium and Tantalum-based Phosphate Glasses and Glass-ceramics for Photonic Applications},
 	year = {2024},
 	url = "https://bdtd.unifal-mg.edu.br:8443/handle/tede/2454",
 	abstract = "Tantalum and Niobium-containing alkaline phosphate glasses are relevant materials for photonic applications due to several properties such as high thermal, chemical and mechanical stability, wide optical window, low phonon energy and high quantum efficiency of luminescent ions. The highest amount of their respective oxides reported in a phosphate glass is 50 mol%, with tantalum or niobium-rich regions that can induce precipitation of crystalline phase of type M2N8O21 (M = Na or K and N = Nb or Ta). In addition to these relevant properties, tantalum/niobium phosphate glasses have a low production cost due to the abundance of starting materials and national strategic relevance, since they are considered strategic elements for technology development. Therefore, these glass and glass-ceramic materials are promising as luminescent matrices, non-linear optical materials for second harmonic generation and substrates for microstructuration of optical properties. Thus, this work may be separated in three main parts: i) study of sodium phosphate glasses with the addition of tantalum oxide from 40 to 50 mol%, as well as the Eu3+-doped glasses and their behavior under Thermal Poling and Micropoling. These glasses were analyzed by Differential Scanning Calorimetry, X-ray Diffraction, Raman and Infrared spectroscopies, Refractive Index, transparency in the UV-Vis region and luminescence. Based on these data, it was verified that the addition of tantalum increases the glass transition temperature, i.e., increasing the connectivity of the glass network; the band-gap shift to longer wavelengths with high transparency (~80%); relatively high refractive index (~1.9 at 532 nm); and strongly modifies the 7F2/7F1 asymmetry ratio in Eu3+-doped glasses. Some of these glasses were thermally poled using a microstructured electrode, under 250°C and voltage from 600 to 900V depending on the glass composition. Maker Fringes measurements confirmed Second Harmonic Generation (SHG) in the poled glasses attributed to Electric Field Induced Second Harmonic (EFISH) model, as well as by the correlative measurements of micro-SHG/Raman/Luminescence in one of them. The microstructured electrode allowed the microprinting of patterns on the glasses, according to micrographs and Atomic Force Microscopy measurements, with changes in the topology, in refractive index and an edge effect of SHG, suggesting a microscale control of the optical properties. ii) study of phosphate glass-ceramics (GC) containing 47.5 mol% of tantalum oxide doped with europium and its behavior under Thermal Poling. Translucent glass-ceramics containing Na2Ta8O21 crystalline phase were obtained with the degree of crystallinity and transparency controlled as a function of the heat treatment time. By photoluminescence it was verified that the europium ions are present in the crystalline phase; since, among others, the ratio of [5D0 →] 7F2/ 7F1 transitions decreases with the increase of the degree of crystallinity. Some of these GC were thermally poled. Measurements of electric current during poling, Time of Flight Secondary-Ion Mass Spectrometry, Infrared and Maker Fringes allowed to establish a model for ion migration under electric field: it appears that sodium ions in the crystalline phase do not migrate within the material, but only those that are still within the glassy phase, with the main change occurring in the phosphate structure after sodium depletion. Also, SHG of GC appears to be originated from EFISH effect after thermal poling as in precursor glasses. Calculated values of χ(2) in GC are one magnitude lower than the respective poled glass. And iii) study of phosphate glasses containing 45 mol% of niobium oxide with increasing amounts of silver and also co-doping with antimony, as well as its preliminary evaluation under Thermal Poling. High silver contents could be incorporated, reaching ~9 mol% in potassium-based glasses and ~5 mol% in sodium-based glasses. Silver increment in these glasses decreases Tg, that is, network connectivity; as well as thermal stability against crystallization with silver acting as a nucleating center. Silver addition also red-shifts the band-gap and increases refractive index. Sodium silver/antimony co-doped glasses present different colors, and consequently, absorption spectra when varying annealing temperature. The glass annealed at Tg exhibits a band related to plasmon resonance not appearing for lower annealing temperatures. One of these glasses - with sodium and 5 mol% of silver - was submitted to Thermal Poling at 300°C/1kV and investigated by Energy Dispersive Spectroscopy. It was verified that not only sodium ions but also silver ions are depleted beneath the anode surface and accumulate below the poled layer.",
 	publisher = {Universidade Federal de Alfenas},
 	scholl = {Programa de Pós-Graduação em Química},
 	note = {Instituto de Ciências Exatas}
}