Desenvolvimento de monólitos vítreos sílicoaluminosos dopados com lantanídeos pelo processo sol-gel com perspectivas de uso em lasers.

Abstract

The sol-gel process is one of the synthetic methods for obtaining materials at low temperatures, with specific properties and high purity. Specifically, it is based on polymerization reactions, and use of alkoxide precursor dissolved in organic solvents. The method can be used to obtain systems with great potential for photonic applications. Among the major laser activators, there are the lanthanide ions, which can be used as dopants in glassy materials. Thus, this study aimed to develop pure vitreous silico-aluminous monoliths pure and doped with neodymium, erbium and holmium ions by the sol-gel process, via acid catalysis. The molar ratios of tetraethylorthosilicate (TEOS) : absolute ethanol : deionized water : aluminum acetate : nitric acid were 1 : 2 : 2 : 0.03 : 0.05 mol, respectively. For all the monoliths same proportions were used, differing only the percentage of lanthanide ions (0.5%, 1%, 2%, 4%, 5% and 10%) and the type of solution (A or B). Solution A was obtained by dissolving the lanthanide oxide in hydrochloric acid (HCl), which was performed backwashing with deionized water and ethanol, while for the solution B was not applied backwash process, only dissolved oxides in hydrochloric acid and ethanol. To obtain the monoliths were added precursor solutions in a flask, and the system was maintained at 60°C under stirring for 2h. To control the drying time, the containers (molds + mixture) were weighed and monitored for 50 days. After the drying time, the monoliths were subjected to heat treatment at 250°C for one hour. The monoliths were characterized by Thermogravimetry (TG), Differential Thermal Analysis (DTA), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Vickers Microhardness (VH), Fourier Transform Infrared Spectroscopy (FTIR), Ultraviolet–visible Spectroscopy (UV-VIS) and Luminescence Spectroscopy (LS). The sol-gel process was effective in obtaining pure monoliths and doped with neodymium, erbium and holmium in different percentages. The minimum and maximum drying time there were 17 and 25 days, respectively. From TG/DTG curves, it has been found that the thermal stability of the monolith decreases with increasing percentage of the lanthanide ion, verified by the increase on the weight loss, attributed to a greater disorder of the system. From XRD, bands were observed with a maximum intensity at 23°(2θ), which characterizes amorphous materials. From FTIR, there was a band offset at approximately 950 cm-1, attributed to the lanthanide ion. It also has been found UV spectrum maximum peaks around 574, 376 and 450 nm corresponding to transitions of the neodymium, erbium and holmium ions, respectively. From the luminescence spectroscopy of neodymiumdoped vitreous monoliths, it has been found emissions related to transitions 4F3/2 → 4 I11/2 and 4F3/2 → 4 I13/2, 1060, and 1340 nm, respectively. For the ones doped with erbium, emission was observed regarding the transition 4 I13/2 → 4I15/2 at 1520nm. The intensities of the emissions were higher for the monoliths doped with neodymium ions from the solution B of the lanthanide ion, with greater intensity for the one doped with 2% (2% Nd3+[B]25). Thus, the vitreous monoliths doped with lanthanide ions a has great potential for applications in photonic devices, as the active mean for solid-state lasers.