Eduardo H.L. Falcão

Semiempirical calculations of aniline oligomers hyperpolarisabilities

Theoretical study of the hyperpolarisabilities β and γ of aniline oligomers is presented. The results obtained for β at the AM1/TDHF level are promising for the emeraldine form, indicating a potential use as a second-order nonlinear optical material. The calculations of static cubic hyperpolarisability of trimers agree with the experimentally observed trends for polyaniline.

First hyperpolarizability and multiphoton induced fluorescence in different forms of polyaniline

The first hyperpolarizability β per monomeric residue of polyaniline in three oxidation states and in the doped emeraldine salt form was determined by hyper-Rayleigh scattering. Multiphoton induced fluorescence was observed and, together with light absorption at the fundamental (ω) and double (2ω) frequencies was taken into account in the calculation of β.

Intensity-dependent excitonic dephasing in polyaniline

The first observation of light intensity-dependent dephasing time, s2, of molecular excitons in polyaniline is reported. Using time-resolved four-wave mixing we observed an increase of s2 when the pump intensity is increased. This unusual behavior is attributed to the excitation of torsional Raman modes associated to the phenyl rings, which contribute to strong confinement of the molecular excitons, as well as to blue shift the polyaniline energy gap and intragap energy levels.

Urchin-like artificial gallium oxide nanowires grown by a novel MOCVD/CVD-based route for random laser application

A novel procedure based on a two-step method was developed to obtain β-Ga2O3 nanowires by the chemical vapor deposition (CVD) method. The first step consists in the gallium micro-spheres growth inside a metal-organic chemical vapor deposition environment, using an organometallic precursor. Nanoscale spheres covering the microspheres were obtained. The second step involves the CVD oxidization of the gallium micro-spheres, which allow the formation of β-Ga2O3 nanowires on the micro-sphere surface, with the final result being a nanostructure mimicking natures sea urchin morphology. The grown nanomaterial is characterized by several techniques, including X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray, transmission electron microscopy, and photoluminescence. A discussion about the growth mechanism and the optical properties of the β-Ga2O3 material is presented considering its unknown true bandgap value (extending from 4.4 to 5.68 eV). As an application, the scattering properties of t...

Polyaniline-Poly(Vinyl Alcohol) Composite: Spectroscopic Characterization and Diffraction Grating Recording

Diffraction gratings were recorded both optically and interferometrically in dichromated poly(vinyl alcohol) (DCPVA) films by means of dichromate photoreduction. Aniline was used as a chemical developer, through in situ polymerization in the unreduced parts of the film. The resulting composite material shows the optical and chemical properties of polyaniline and the mechanical resistance of PVA. Characterization of the gratings gave a line width of 12.2 μm and a diffraction efficiency of 32 %. Uv-vis spectroscopy was used to study dichromate photoreduction and the optical properties of the composite..

Magnetic Properties of Organic Acid-Doped Polyaniline

Magnetization and magnetic susceptibility of pellets of polyaniline basic- EB and acid doped-ES(HCOOH) and ES(HCl) were measured as a function of the temperature and magnetic field. Few but large magnetic moments are responsible for the magnetism in these materials.