I. Guedes

Spectroscopic properties of Er3+-doped lead phosphate glasses for photonic application

The spectroscopic characteristics of Er3+-doped lead phosphate glasses have been investigated, and Judd?Ofelt analysis was used to evaluate the effect of increasing the Er3+ content on the glass matrices. The intensity-dependent Judd?Ofelt parameters, ?(4) and ?(6), remained constant while ?(2) decreased. The concentration quenching effect on the lifetime of the Er3+?:?4I13/2 ?4 I15/2 (1530?nm) transition is also evaluated as a result of the addition of Er3+ to the lead phosphate glass composition. The observed relatively large reduction in the lifetime reflects the significant effects of non-radiative processes in this system. The potential use of these glasses as photonic devices is also discussed.

Characterization of Buriti (Mauritia flexuosa L.) oil by absorption and emission spectroscopies

Amostras de oleo obtido do fruto do Buriti (Mauritia flexuosa L.) foram caracterizadas por espectroscopia de absorcao e emissao. O espectro de absorcao foi obtido no intervalo de 300 a 2000 nm, enquanto o espectro de emissao foi analisado entre 400 e 800 nm, onde observamos varias bandas. Para melhor entender a complexidade destes espectros, tambem obtivemos os espectros de absorcao e emissao dos componentes majoritarios do oleo de Buriti. Correlacionando estes dados, apresentamos uma discussao sobre a origem das bandas observadas.

Raman investigation of A2CoBO6 (A=Sr and Ca, B=Te and W) double perovskites

Raman scattering is used to investigate the room temperature phonons of tetragonal (I4∕m) Sr2CoWO6 and monoclinic (P21∕n) Ca2CoWO6, Sr2CoTeO6, and Ca2CoTeO6 double perovskites. Both tetragonal and monoclinic structures result from small distortions of the Fm3¯m cubic lattice. Therefore, phonons were assigned according to correlations with those observed in the prototype A2B′B″O6 Fm3¯m cubic structure and the internal vibrational modes of the oxygen octahedra. The observed shifts of some vibrations in the A2CoBO6 compounds upon changing either A or B elements are tentatively explained.Raman scattering is used to investigate the room temperature phonons of tetragonal (I4∕m) Sr2CoWO6 and monoclinic (P21∕n) Ca2CoWO6, Sr2CoTeO6, and Ca2CoTeO6 double perovskites. Both tetragonal and monoclinic structures result from small distortions of the Fm3¯m cubic lattice. Therefore, phonons were assigned according to correlations with those observed in the prototype A2B′B″O6 Fm3¯m cubic structure and the internal vibrational modes of the oxygen octahedra. The observed shifts of some vibrations in the A2CoBO6 compounds upon changing either A or B elements are tentatively explained.

Polarized Raman Spectra and Infrared Analysis of Vibrational Modes in L-Threonine Crystals

Polarized Raman and infrared espectra of l-threonine crystals have been obtained at room temperature and an assignment of normal modes is proposed based on group theory analysis. The usefulness of these assignments comes from the fact that some modes are related to important vibrations that can show changes under different pressure and temperature conditions.

Raman investigations of rare earth orthovanadates

Polarized Raman spectroscopy has been used to obtain the room-temperature phonon spectra of the series of rare earth orthovanadate single crystals: SmVO4, HoVO4, YbVO4, and LuVO4. The observed Raman frequencies follow the overall mode distribution expected for REVO4 compounds with the tetragonal zircon structure. The variation of the mode frequency with atomic number across the lanthanide orthovanadate series was investigated, and the trend exhibited by the internal modes was explained by considering the force constants of VO4 tetrahedron.

Monoclinic phase ofPbZr0.52Ti0.48O3ceramics: Raman and phenomenological thermodynamic studies

This work reports on the first Raman detection of the tetragonal to monoclinic phase transition in PZT ceramics near morphotropic phase boundary at low temperatures. The transition is characterized by changes in the frequency of lattice modes with the temperature. The results presented here confirm the previous one recently reported by Noheda et al. using high-resolution synchrotron X-ray powder diffraction technique and dielectric measurements. The stability of the new phase is discussed within the framework of phenomenological Landau-Devonshire Theory.

Raman scattering study of Tb(V1−xPx)O4 single crystals

The polarized Raman spectra of a series of isostructural vanadate/phosphate compounds of the form: Tb(V1−xPx)O4 with 0⩽x⩽0.75 have been investigated at room temperature. While the observed Raman spectra are generally consistent with group theory predictions for a body-centered tetragonal crystal structure (D4h19), due to the replacement of P for V, additional spectral features induced by the disorder of the mixed vanadate/phosphate system are also observed. In particular, all of the external lattice modes are characterized by a one-phonon-like behavior, while the behavior of the internal modes of the (V,P)O4 tetrahedron is two-phonon-like.

Control of luminescence emitted by Cd1 − xMnxS nanocrystals in a glass matrix: x concentration and thermal annealing

Cd(1-x)Mn(x)S nanocrystals (NCs) were successfully grown in a glass matrix and investigated by photoluminescence (PL), electron paramagnetic resonance (EPR) and magnetic force microscopy (MFM). We verified that the luminescent properties of these NCs can be controlled both by changing the x concentration and by thermal annealing of the samples. The EPR and PL data showed that the characteristic emission of Mn(2+) ions ((4)T(1)-(6)A(1)) is only observed when this magnetic impurity is substitutionally incorporated in the Cd(1-x)Mn(x)S NC core (site S(I)). Besides, it was observed that the emission ((4)T(1)-(6)A(1)) suppression, caused by the Mn(2+) ion presence near the surface (site S(II)) of the Cd(1-x)Mn(x)S NCs, is independent of the host material. The MFM images also confirmed the high quality of the Cd(1 - x)Mn(x)S NC samples, showing a uniform distribution of total magnetic moments in the nanoparticles.

Optical characterization of Nd3+- and Er3+-doped lead-indium-phosphate glasses

In this work, Judd–Ofelt analysis is applied to rare-earth-doped lead-indium-phosphate glasses (RE-PbInPO4, where RE=Er3+ and Nd3+) in order to evaluate their potential as both glass laser systems and amplifier materials. The phenomenological Judd–Ofelt parameters Ω(2), Ω(4), and Ω(6) are determined for both rare-earth ions together with their quality factors and compared with the equivalent parameters for several other host glasses. The spontaneous emission probabilities and the lifetimes of the Nd3+ F43/2 laser transitions are determined and analyzed as a function of the optical quality factor. For Nd3+-PbInPO4, glass fluorescence emission (890, 1058, and 1330 nm) lines are observed. Highly efficient infrared-to-visible frequency up-conversion at 530, 550, and 670 nm as well as an intense infrared fluorescence emission (∼1540 nm) is observed in Er3+-doped PbIn(PO4) glasses pumped using 800 nm radiation excitation.

Quantum efficiencies and thermo-optical properties of Er3+-, Nd3+-, and Pr3+-single doped lead-indium-phosphate glasses

The experimental determination of thermal and optical properties, such as the fluorescence quantum efficiency (η) and temperature coefficient of the optical path length change (ds/dT) have been a challenging task. In this work, mode-mismatched thermal lens and spectroscopic measurements were performed using Er3+-, Nd3+-, and Pr3+-doped lead-indium-phosphate glasses to obtain the thermal diffusivity and conductivity, ds/dT, the thermal loading (nonradiative quantum efficiency), and η. The experimental difficulties associated with obtaining η for systems with several emitting levels, such as Er3+-doped materials were overcome. A discussion of the implications of the small η values obtained for Er3+- and Pr3+-doped glass is presented.