Search results for "RAMAN"
showing 10 items of 1328 documents
Integrated experimental and theoretical study on the phase transition and photoluminescent properties of ZrO2:xTb3+ (x=1, 2, 4 and 8 mol %)
2021
Abstract Zirconia (ZrO2) has been intensively studied as an important ceramic material, and numerous technological applications have been found. The present work deals with synthesizing and characterizing the phase transition (cubic vs tetragonal) and photoluminescence emissions of ZrO2:xTb3+ (x = 1,2,4 and 8 mol%). The samples formed by the complex polymerization were thoroughly characterized for physicochemical properties such powder by X-ray diffraction (XRD), and Raman and diffuse reflectance spectroscopies. First-principle calculations at the density functional theory level were performed to complement and rationalize the experimental results. An energy transfer mechanism which promote…
Differential scanning calorimetric and Raman studies of phase transition V ⇌ IV of ammonium nitrate
1993
Abstract Differential scanning calorimetry, alone and in conjunction with Raman spectrophotometry for simultaneous calorimetric and spectral measurements, was used to study the solid state phase transitions of ammonium nitrate between − 50 and 100 °C. On heating, two transition paths were observed between − 40 and 0 °C: one showing two separate peaks in DSC and the other showing a single peak. The latter path became dominant when samples were thermally cycled. The double transition was followed by transition IV →II at 51 °C and the single transition by transitions IV → III → II at about 50 and 87 °C. Raman spectra showed that there were two phases present between the two DSC peaks at low te…
Excitonic effects in two-LO-phonon resonant Raman scattering.
1993
Abstract The role of electron-hole correlation in resonant Raman scattering by two LO-phonons is analyzed. A theoretical model including excitons belonging to the discrete and continuous spectra as virtual intermediate states in the Raman process and valid for incident energies below and above the gap is developed. For the exciton-phonon coupling the Frohlich Hamiltonian is considered. The most important contribution to the Raman scattering efficiency corresponds to the continuous→discrete→discrete exciton transition, followed by the discrete→discrete→discrete and the continuous→continuous→discrete ones. The model is tested for GaP, where the scattering efficiency data are available around …
On the interpretation of the experimental Raman spectrum of β-eucryptite LiAlSiO4 from atomistic computer modeling
2000
Abstract The vibrational spectrum of β-eucryptite LiAlSiO4 with stuffed high quartz structure – commercially relevant for zero-expansion glass ceramics – was calculated by lattice energy minimization and diagonalization of the dynamical matrix using an ab initio based ion-pair shell model potential. A full symmetry analysis of the vibrational modes was carried out. Raman activity of vibrations was calculated under parameterization of individual polarizability factors for each type of interatomic bonds in β-eucryptite LiAlSiO4. Calculated vibrational energies agree with the experimental energies within ±2.3%. Agreement of calculated spectroscopic Raman intensities with experimental intensiti…
Symmetry-species conversion in CD3systems
1993
The rates for symmetry-species conversion of CD3 groups are calculated using a model in which the interaction between the quadrupolar moment of the deuterons with electric-field gradient at the site of the nucleus causes symmetry-changing transitions. Just the same phonons are considered for energy conservation as are used to describe the temperature dependence of inelastic neutron scattering experiments. For the conversion rate, a similar temperature dependence is found as has already been obtained for CH3. For temperatures around the tunnelling energy, a behaviour is predicted for CD3 that is different from the behaviour in protonated systems according to all theories known to the authors…
Time-resolved coherent anti-Stokes Raman-scattering measurements of I2 in solid Kr: vibrational dephasing on the ground electronic state at 2.6-32 K.
2005
Time-resolved coherent anti-Stokes Raman-scattering (CARS) measurements are carried out for iodine (I2) in solid krypton matrices. The dependence of vibrational dephasing time on temperature and vibrational quantum number v is studied. The v dependence is approximately quadratic, while the temperature dependence of both vibrational dephasing and spectral shift, although weak, fits the exponential form characteristic of dephasing by pseudolocal phonons. The analysis of the data indicates that the frequency of the pseudolocal phonons is approximately 30 cm(-1). The longest dephasing times are observed for v = 2 being approximately 300 ps and limited by inhomogeneous broadening. An increase in…
Time-Resolved Coherent Anti-Stokes Raman Scattering of Graphene: Dephasing Dynamics of Optical Phonon.
2017
We report dynamics of the G-mode in graphene probed with time-resolved coherent anti-Stokes Raman scattering measurements. By applying BOXCARS excitation geometry with three different excitation wavelengths, various nonlinear processes can be selectively detected due to energy and momentum conservation and temporal sequence of the pulses. The Raman signal due to resonant coherent excitation of the G-mode shows exponential decay with lifetime of ∼325 ± 50 fs. This decay time is shorter than expected based on the line width of the G-mode in the Raman spectrum. We propose that the unexpectedly short dephasing time is a result of dynamic variation of nonadiabatic coupling of the photoexcited el…
Preparation of N-doped TiO2: characterization and photocatalytic performance under UV and visibile light
2009
Nanocrystalline N-doped TiO(2) samples were prepared by using TiCl(4) or TiOSO(4) as precursors. The powders were characterized by X-ray diffraction, BET specific surface area measurements, scanning electron microscopy, diffuse reflectance spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The photocatalytic activity was tested using the photodegradation of 4-nitrophenol under UV and visible light.Some samples were more active than commercial Degussa P25. A shift of the absorption edge to a lower energy and a stronger absorption in the visible light region were observed in the samples obtained from TiCl(4). Two absorption edges were observed in the samples derived from T…
Synergistic effect between hydrodynamic conditions during Ti anodization and acidic treatment on the photoelectric properties of TiO2 nanotubes
2015
In the present work, the combined influence of controlled hydrodynamic conditions during Ti anodization and the acidic treatment with HClO4 on the photoelectric properties of mixed anatase/rutile TiO2 nanotubes has been studied. Anodized samples were analyzed by means of Field Emission Scanning Electronic Microscopy (FE-SEM), Confocal Raman Microscopy, electrochemical measurements (electrochemical impedance spectroscopy and Mott-Schottky analysis) and photoelectrochemical measurements. It has been observed that the use of hydrodynamic conditions increases the surface area of nanotubes, while acidic treatment enhances their conductivity. Besides, there is a clear synergistic effect between t…
Photoelectrochemical Evidence of Cu2O/TiO2 Nanotubes Hetero-Junctions formation and their Physicochemical Characterization
2014
Cu2O/TiO2 nanotubes heterojunctions were fabricated by electrochemical deposition of cuprous oxide on TiO2 nanotubes arrays grown by anodizing. X-ray diffraction and Raman Spectroscopy analysis allows for identification of Cu2O, whose morphological features were studied by Scanning Electron Microscopy as a function of the charge circulated during the electrodeposition step. Photoelectrochemical measurements in aqueous solutions evidenced a red shift of the light absorption threshold of TiO2 nanotubes due to the presence of cuprous oxide even for very low circulated charges, while electrochemical impedance measurements proved a significant reduction of the electrode impedance due the presenc…