Influência da co-dopagem com íons La3+ em sistemas binários de óxidos de SiO2-TiO2:Eu3+ obtidos pelo método sol-gel

Abstract

This study investigates the synthesis and characterization of photoluminescent materials based on SiO2-TiO2 matrices co-doped with Eu3+ and La3+. Prepared via the sol-gel method and calcined at 750 °C, the matrices were analyzed by X-ray Diffraction (XRD), Raman spectroscopy, Fourier-Transform Infrared spectroscopy (FTIR), Diffuse Reflectance Spectroscopy (DRS), Scanning Electron Microscopy (SEM), and Photoluminescence (PL). Structural results confirmed the stabilization of the anatase phase, where the incorporation of La3+ acted as a crystal growth inhibitor, except at concentrations of 0.3 and 1.0 mol%, which exhibited a singular bulk-like behavior regime. Diffuse reflectance analysis (DRS) revealed an adjustable direct band gap between 2.75 and 3.02 eV, correlated with the structural disorder monitored by the Urbach energy. Thermal treatment proved crucial, promoting the removal of hydroxyl suppressors and resulting in an average 6.5-fold (547%) jump in luminescence lifetimes (τ), which reached values exceeding 1000 µs. Spectroscopic analysis indicated that La3+ co-doping induces a symmetry breaking at the Eu3+ local site (site symmetries Cs, Cn ou Cnv), evidenced by the splitting of the 5D0→7F1 transition into three singlets and a 120% increase in the emission intensity of the 5D0→7F2 hypersensitive band. In situ PL monitoring as a function of temperature confirmed the reversibility and thermal robustness of the system, mitigating quenching effects. These findings demonstrate the high potential of SiO2-TiO2:Eu3+,La3+ composites for the development of advanced photonic devices, such as WLEDs and high-sensitivity sensors for optical thermometry.