1,721,037 research outputs found
Linewidth behavior of the A1g Raman phonon in CdxHg1-xI2 solid solution
No full textThe behavior of the A1g phonon line in CdxHg1-xI2 (with 0<x<0.38) solid solution has been investigated by Raman spectroscopy between 20 and 300 K. At room temperature, the A1g linewidth unexpectedly decreases as the cadmium concentration is increased; at low temperature, the more conventional opposite trend is observed. By taking into account a variation of the final density of states in which the A1g phonon decays, a convincing explanation of the experimental results is given. In addition, useful information on the behavior of the boundary LO(X) and/or LA(X) phonons in the solid solution can be extracted
Anharmonic mixing between two phonons in red mercury iodide
No full textWith use of Raman spectroscopy we have investigated the anharmonic mixing between two optical phonons of Eg symmetry in red mercury iodide. By taking into account the presence of several decay channels contributing to phonon lifetime, the experimental line-shape anomalies due to mode coupling have been reproduced with good accuracy. The temperature behavior of the anharmonic interaction is in agreement with theory
Thermodynamics of optically assisted desorption of oxygen from TiO2 nanoparticle surface
No full textThe thermodynamics of oxygen desorption from TiO2 crystals under steady
light excitation is investigated. The non-equilibrium photo-induced processes
are explicitly accounted for by considering the rate of entropy
production. The adsorption/desorption properties of oxygen on anatase
nanocrystals are investigated as a function of the pressure of the experimental
room and a generalized Langmuir–Fowler equation is obtained for the
case of photo-assisted surface processes. The kinetic scheme used for this
study involves color centers and surface centers on the Ti3C sites. In particular,
oxygen depletion is forced by recombinations of electrons trapped
in bonding sites and holes trapped in color centers (FC centers)
PHOTOLUMINESCENT AND PARAMAGNETIC CENTERS IN GAMMA IRRADIATED POROUS SILICA
No full texthe photolummescence and electron spin resonance properties of gamma irradiated (up to 500 kGy) porous silica are reported. By exciting at 5.6 eV a photoluminescence contribution can be detected before irradiation, peaked at about 4.1 eV. Gamma irradiation causes the generation of the E' centers (about 1 x 10(14) defects cm(-3)) of paramagnetic hole centers and modifies the photoluminescence properties of the sample: the emission amplitude decreases and three contributions can be singled out at about 3.3, 3.8 and 4.4 eV
Raman Scattering from Vibrational Modes in Layered CdxHg1–xI2 Solid Solution
No full textRaman spectra at 15 and 300 K of CdxHg1–xI2 solid solutions for 0 < x < 0.44 are investigated. One mode behaviour is observed for the low frequency phonons and the A1g mode, while a two mode behaviour is exhibited by the higher frequency vibrations. The expected mass, force, and temperature induced splitting of the B1g2 and Eg1 degenerated modes is not observed. This fact proposes another different experimental evidence of the low Raman cross section of the B1g2 rigid layer mode. For the first time the degeneracy of the Eg2 mode with the A1g is lifted and experimentally found
Hybrid materials for solid-state dye laser applications
No full textThe quest for a solid-state tunable dye laser can be satisfied by sol-gel prepared organic-inorganic hybrids. A photostability study of porous silica-Rhodamine 6G hybrids prepared via a sol-gel method is presented. The dye molecules can be incorporated into the silica matrix by forming weak or covalent bonds (hybrids of classes I and II, respectively). New class II samples and traditional class I materials prepared by the predoping method were synthesized. Samples were characterized by photoluminescence measurements to compare the emission properties and the photostability of the samples. The decay of the fluorescence signal as the cumulative excitation energy increases is reported and interpreted by hypothesizing that the dye molecules can be hosted in different surroundings within the porous glass matrix. The reported photoluminescence and photobleaching features indicate the class II samples as good candidates for solid-state dye lasers
Photoluminescent and paramagnetic centers in gamma irradiated porous silica
No full textThe photolummescence and electron spin resonance properties of gamma irradiated (up to 500 kGy) porous silica are reported. By exciting at 5.6 eV a photoluminescence contribution can be detected before irradiation, peaked at about 4.1 eV. Gamma irradiation causes the generation of the E' centers (about 1 x 10(14) defects cm(-3)) of paramagnetic hole centers and modifies the photoluminescence properties of the sample: the emission amplitude decreases and three contributions can be singled out at about 3.3, 3.8 and 4.4 eV. (c) 2005 Elsevier B.V. All rights reserved
Long term therapy with methylphenidate induces modest effects on growth in ADHD children
No full text- …
