F. E. A. Melo

Optical properties of Sm3+ doped lead fluoroborate glasses

We present a study of emission, absorption and vibrational properties of Sm3+ doped lead fluoroborate glasses (PbO–PbF2–B2O3–Sm2O3) as a function of the Sm3+ content. Changes in the position and the intensity parameters of the transitions are closely related to structural changes in the glass network. A Judd–Ofelt scheme was used to estimate the intensity parameters Ωλ and radiative properties for Sm3+ in the glass. The behaviour of Ω2 and Ω6 parameters suggested a decrease in the asymmetry degree of the local ligand field at Sm3+ sites and an increase in the covalency of Sm–O bond, respectively. This hypothesis was verified by analysing the structural role of Sm2O3 through Raman and infrared spectroscopy measurements.

Optical properties of L-alanine Organic Crystals

This work reports on the optical properties of L-alanine crystals grown from aqueous solution using the well-known slow evaporation method. Linear properties including absorption spectra and refractive indices are determined, as well as nonlinear properties of second harmonic generation (SHG), such as the phase-matching loci and efficiency. Although the SHG efficiency is smaller than those of other known materials, the study of L-alanine crystals is very important since it is part of more complex aminoacids including L-arginine and asparagine, with much higher SHG efficiency. Some mechanical properties are also presented, namely hardness and thermal expansion coefficients.

High-pressure Raman study of L-alanine crystal

Abstract Single-crystal samples of l -alanine, CH 3 CH(NH 2 )COOH, a fundamental amino acid of most proteins, have been studied by Raman spectroscopy in a diamond-anvil cell up to pressures of 43xa0kbar. From the analysis of results we observed that the crystal undergoes a phase transition about 22–23xa0kbar. The transition is accompanied by abrupt changes in the relative intensity of low-energy bands, by the appearance of a phonon in the external mode region of the spectrum and by some modifications in phonons of the internal mode type.

Raman study of morphotropic phase boundary in PbZr 1 − x Ti x O 3 at low temperatures

The Raman spectra of

Pressure-induced phase transitions in monohydrated l-asparagine aminoacid crystals

{mathrm{PbZr}}_{1ensuremath{-}x}{mathrm{Ti}}_{x}{mathrm{O}}_{3}

Raman scattering studies of monohydrated L-asparagine

ceramics with titanium concentration varying between

High‐pressure Raman study of taurine crystal

x=0.40

Phase transitions in LiKSO4

and 0.60 were measured at 7 K. By observing the concentration-frequency dependence of the vibrational modes, we identified the boundaries among the rhombohedral, monoclinic, and tetragonal ferroelectric phases. The analysis of the spectra was made in the view of group theory analysis making possible the assignment of some modes for the monoclinic phase.

High-pressure X-ray diffraction of L-ALANINE crystal

Abstract Single-crystal samples of monohydrated l-asparagine, C4N2O3H8. H2O, a fundamental aminoacid of the human body and other complex beings, have been studied by Raman spectroscopy in a diamond-anvil cell up to pressures of 2.0 GPa. From the analysis of results we observed that the crystal undergoes a series of three phase transitions. All transitions are accompanied by drastic changes in the external modes and in some internal modes of the crystal, which shows in a clear way the transitions induced by the hydrostatic pressure. Pressure coefficients for external modes are also given.

Polarized Raman and Infrared Spectra of Taurine Crystals

Polarized first-order Raman scattering studies at 300 K were carried out in L-asparagine monohydrate crystal in order to obtain the general assignment of its phonon spectra. A careful analysis of the vibrational spectra shows that the assignment of the fundamental vibrational modes can be done on the basis of amino, carboxilic and water groups vibrations, and correlations with previous data reported for other amino acids. However, some vibrations were correctly assigned from the study of its temperature - dependence behavior performed in the range 10 - 300 K. The assignment proposed cofirm the zwitterionic structure of L-asparagine monohydrate crystal.