RESUMO
This paper demonstrates that femtosecond laser-irradiated Fe2O3 materials containing a mixture of α-Fe2O3 and ε-Fe2O3 phases showed significant improvement in their photoelectrochemical performance and magnetic and optical properties. The absence of Raman-active vibrational modes in the irradiated samples and the changes in charge carrier emission observed in the photocurrent density results indicate an increase in the density of defects and distortions in the crystalline lattice when compared to the nonirradiated ones. The magnetization measurements at room temperature for the nonirradiated samples revealed a weak ferromagnetic behavior, whereas the irradiated samples exhibited a strong one. The optical properties showed a reduction in the band gap energy and a higher conductivity for the irradiated materials, causing a higher current density. Due to the high performance observed, it can be applied in dye-sensitized solar cells and water splitting processes. Quantum mechanical calculations based on density functional theory are in accordance with the experimental results, contributing to the elucidation of the changes caused by femtosecond laser irradiation at the molecular level, evaluating structural, energetic, and vibrational frequency parameters. The surface simulations enable the construction of a diagram that elucidates the changes in nanoparticle morphologies.
RESUMO
Ultrafine PbZr0.20Ti0.80O3 was amorphized through high-energy mechanical milling. The structural evolution through the amorphization process was accompanied by various characterization techniques, such as X-ray diffraction, Fourier-transformed IR spectroscopy (FTIR), high-resolution transmission electron microscopy (HR-TEM), and Raman spectroscopy. A strong photoluminescence was measured at room temperature for amorphized PbZr0.20Ti0.80O3, and interpreted by means of high-level quantum mechanical calculations in the density functional theory framework. Three periodic models were used to represent the crystalline and amorphized PbZr0.20Ti0.80O3, and they allowed the calculation of electronic properties that are consistent with the experimental data and that explain the appearance of photoluminescence.
RESUMO
This work describes the synthesis, at room temperature, of doped and undoped SnO2 nanocrystals (particle size ranging from 1-3 nm) with no thermal or hydrothermal treatment. To the best of our knowledge, this is the first time that the synthesis, at room temperature, of doped and/or undoped SnO2 nanocrystals has been reported. This new synthesis method is based on the controlled oxidation, hydrolysis and polycondensation of tin ions in an ethanol solution. Another novel aspect of this method is the possibility of using surfactants, which may provide improved control over the particle size.