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The effect of high pressure (7.7 GPa) densification on the absorption and near-infrared emission of Nd-doped lithium, sodium and potassium disilicate glasses was investigated. Judd-Ofelt parameters O¿ (¿ = 2, 4 and 6) were calculated from the absorption spectra, before and after densification of glasses, indicating that the irreversible structural changes induced by pressure increased the symmetry of the Nd-O bonding. Density and refractive index of the glasses also increased, probably related to the close packing of SiO4 tetrahedra during densification. The magnitude of the splitting due to the Stark effect was larger for potassium silicate, before and after densification. The radiative transition probabilities of the hypersensitive transition for sodium and potassium silicate increased after densification while the radiative lifetime decreased. For lithium silicate, the opposite behavior was observed. The experimental results corroborate the influence of alkali ion and densification on the luminescence properties of Nd-doped alkali silicate glasses

TiO2/SiO2 nanoparticles with 3, 5, and 10 molar percent of silica, were synthesized by hydrothermal method and characterized by SEM, TEM, N2 adsorption-desorption isotherms, X-ray diffraction, and Raman and UV-Vis spectroscopy. While pristine TiO2 thermally treated at 500°C presents a surface area of 36 m2g-1(±10 m2g-1), TiO2/SiO2 containing 3, 5, and 10 molar percent of silica present surface areas of 93, 124, and 150 m2g-1(±10 m2g-1), respectively. SiO2is found to form very small amorphous domains well dispersed in the TiO2 matrix. X-ray diffraction and Raman spectroscopy data show that anatase-to-rutile phase transition temperature is delayed by the presence of SiO2, enabling single-anatase phase photoanodes for DSSCs. According to the I×V measurements, photoanodes with 3% of SiO2 result in improved efficiency, which is mainly related to increasedsurface area and dye loading. In addition, the results suggest a gain in photocurrent related to the passivation of defects by SiO2

A pressure cell with an anvil made of sapphire and the other made of tungsten carbide, was constructed to process thin film samples using a high power Nd:YAG pulsed laser, in a regime of ultrafast quenching rate and confined geometry. The sapphire anvil worked as the optical window to the laser beam and also as a good thermal conductor substrate. Thin films of amorphous carbon deposited over copper substrate were processed under pressure by Nd:YAG laser pulses. This process induces the formation of a high temperature region at the sample surface during a very short time interval of the order of the 8 ns laser pulse duration. To avoid the complete evaporation of the film, an external pressure of about 0.5 to 1.0 GPa was applied, confining the sample. With the aid of the nanosecond pulsed laser, absorbed on a very thin film sample, this specially designed apparatus provides the means to produce ultrafast quenching as the formation of a plume is suppressed and heat dissipation is accelerated by the high thermal conductivity of the copper substrate and sapphire anvil. The processed samples were analyzed by microRaman spectroscopy and the results indicated the formation of polyynic carbyne structures, as revealed by the presence of a characteristic Raman peak at about 2150 cm-1. Another set of Raman peaks observed at 996, 1116, and 1498 cm-1, also appeared when the amorphous carbon film was processed with a sequence of more than three consecutive laser pulses. These peaks, whose general aspect is very similar to that of polyacethylene (CnHn), could be ascribed to the cumulenic carbyne structure, stabilized by some dispersed copper atoms.

A modification of the one dimensional A ° ngstro¨m’s method that employs photothermal radiometry has been used to determine the longitudinal thermal diffusivity of three thin long bars of chemical vapor deposited diamond. Long bar specimens permit us to use a simple one-dimensional treatment that employs a linear least squares fitting procedure on both magnitude and phase data as a function of position, provided that the condition for ignoring end effects is fulfilled. Any differences in diffusivities obtained from magnitude data and from phase data can be attributed to surface heat losses; the values of diffusivity obtained with the two types of data showed no significant difference. The diffusivities obtained agree reasonably well with the mean values calculated from measurements made by several other laboratories on the same specimens. The heat source was the beam of an argon-ion laser focused onto the specimen surface either with a cylindrical lens to form a line focus or with a spherical lens to form a point focus. The differences in diffusivities obtained when a line source was used and when a point source was used were not statistically significant. A theoretical calculation indicates that the measurements on the specimen were made sufficiently far from the heat source for the one-dimensional treatment to be valid whether the line source or the point source were used: either source is expected to give the same result as was observed experimentally. A point source is preferable because the optical configuration of the experiment is simpler and larger signals are obtainable.

The pressure dependence of the refractive index of monoclinic and yttria-stabilized cubic zirconia was measured up to 3 and 8 GPa, respectively, using an interferometric method with the diamond-anvil cell. The experimental results show a practically linear behavior for both crystalline structures. For cubic zirconia, the refractive index remains practically constant under pressure, while for the biaxial monoclinic phase, one component of the refractive index decreases and the other component increases with pressure, despite the rather isotropic lattice compression in the corresponding crystalline directions. The behavior of the electronic polarizability of the oxygen ion was investigated through the LorentzLorenz relation, yielding the following Mueller parameters: for the cubic phase A0= 1.02, and for the monoclinic phase A0=1.05 for the component nearly parallel to the b direction, and A0=0.85 for the component in the direction of the projection of the "a" axis on the sample plane. In the case of monoclinic zirconia, the behavior of the polarizability under pressure is about 20% more anisotropic than the compression of the respective lattice parameters, indicating a distinct effect of the interatomic interactions over the oxygen íons for the two directions under consideration.