Raman spectra of α-GaTe single crystals

Raman-active lattice vibrational modes of GaTe have been investigated at 300°K in the frequency range 13–300 cm^-1. The spectra of the Bridgman grown crystals were excited with the 1.06 μm line of the continuously operated YAG : Nd³⁺ laser. Fourteen Raman bands were observed. All phonon modes have been assigned on the basis of their observed polarisation dependence to an irreducible representation of the appropriate point group. The results are consistent with the existence of GaTe in monoclinic α-polytype (C³_2h).     

Raman spectra of lithium hydroxide single crystals

First order Raman frequencies, linewidths, intensities and assignments to the symmetry species of all modes predicted by group theory at 20°C and at 78 K are reported for the first time. Assignments of the fundamental frequencies to stretching vibrations or librations of the OH^? ions, internal vibrations of Li⁺ ions of the same layer or translational modes of the Li⁺ and OH^? layers are derived from factor group analysis and correlation methods. They correspond to the constructions of unit cell modes by Wickersheim[2].     

Effect of neutron irradiation on the IR absorption spectra of cupric oxide single crystals

A strong increase of the absorption coefficient with photon energy increasing from 0.1 to 1.0 eV is observed in the spectra of CuO single crystals irradiated with neutrons to a fluence of 5×10¹⁸ cm⁻². The difference of the absorption coefficients before and after irradiation depends on the wavelength as λ⁻². The effect of neutron irradiation on CuO is qualitatively similar to that of neutrons on other semiconductors (for example, GaAs) and differs from that obtained by irradiating CuO with charged particles. Zh. Tekh. Fiz. 69, 98–99 (December 1999)     

Second-order Raman spectra of CsCl single crystals

The second-order Raman spectra of CsCl single crystals have been measured at room temperature for different Raman polarizations and crystal orientations. With the help of the calculated selection rules for a CsCl-type lattice, observed nineteen peaks and shoulders were assigned by the critical point analysis based on the neutron scattering data. By comparing the observed Raman intensities with the thermally weighted two-phonon density-of-states calculated by using a simple shell model, it has turned out that though the measured spectra are dominantly determined by the two-phonon density-of-states, the effect of the q-dependence of the polarizability cannot entirely be neglected.     

Raman spectra of photorefractive lithium niobate single crystals

We have conducted comparative studies of the Raman spectra of lithium niobate (LiNbO₃) crystals of different compositions for excitation in the visible and near IR regions. We have observed that the photorefractive effect is one of the factors leading to line broadening. For this reason, the linewidths may be greater upon Raman excitation in the visible region than for excitation in the near IR region. This may be explained by formation in the crystal, when illuminated by laser radiation in the visible region, of a three-dimensional sublattice of nanostructures and microstructures (with refractive index and other physical parameters different from the parameters of the host crystal) from which photorefractive light scattering occurs. Formation of nanostructures and microstructures makes an additional contribution (besides the contribution due to random and dynamic disorder in the arrangement of the structural units) to the broadening of the Raman lines in the visible region of the spectrum. Illumination of the crystal by radiation in the near IR region does not induce a sublattice of nanostructures and microstructures, due to a significantly smaller photorefractive effect.     

IR absorption and surface-enhanced Raman spectra of the isoquinoline alkaloid berberine

We present the IR absorption and surface-enhanced Raman scattering (SERS) spectra of the isoquinoline alkaloid berberine adsorbed on a silver hydrosol and on the surface of a silver electrode for different potentials. Based on quantum chemical calculations, for the first time we have assigned the vibrations in the berberine molecule according to vibrational mode. The effect of the potential of the silver electrode on the geometry of sorption of the molecule on the surface is considered, assuming a short-range mechanism for enhancement of Raman scattering. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 31–36, January–February, 2007.     

Raman spectra of undoped and uranium doped CaF2 single crystals

Raman scattering experiments for nominally pure and uranium doped CaF2 single crystals were presented.In all crystals, the Raman active T2g vibration mode of CaF2 was observed, whose frequency shift and fullwidth at half-maximum (FWHM) broadening correspond well with defects and impurities in CaF2 lattice.Additional Raman peaks develop in nominally pure CaF2 with high etch pits density and U6+:CaF2crystals. Part of additional Raman peaks in the experimental results, which are assumed due to vibration modes from F- interstitials and vacancies, are in well agreement with the theoretical predications by employing the Green-function formulation.     

73Ge NMR spectra in germanium single crystals with different isotopic composition

We have studied the influence of isotopic disorder on the local deformations in Ge single crystals from both experimental and calculation points of view. The nuclear magnetic resonance (NMR) spectra of⁷³Ge nuclei (the nuclear spin equals 9/2) in perfect single crystals of germanium with different isotopic content were measured at temperatures 80, 300 and 450 K. Abnormal broadening of the spectrum was found to occur when the magnetic field was aligned along the [111] axis of a crystal. The observed specific angular dependence of the quadrupole broadening was attributed to isotopic disorder among atoms of germanium sited around the⁷³Ge NMR probe. Local lattice deformations in germanium crystal lattice due to isotopic impurity atoms were calculated in the framework of the adiabatic bond charge model. The results obtained were applied to study random noncubic crystal field interactions with the nuclear quadrupole moments and corresponding effects in NMR spectra. Simulated second and fourth moments of resonance frequency distributions caused by the magnetic dipole-dipole and electric quadrupole interactions are used to analyze the lineshapes, theoretical predictions agree qualitatively with the experimental data.     

Inelastic alpha-scattering from the stable even germanium isotopes

Scattering of 31.5 MeV α-particles from the stable even Ge isotopes has been studied with an energy resolution of 15–20 keV FWHM. Angular distributions were measured for excitation energies of up to 5.2 MeV. Most of the levels are well described by collective DWBA calculations with vibrational model form factors. An implicit folding procedure was used to derive isoscalar transition rates. The distribution of the isoscalar multipole strength reveals an increasing fragmentation with increasing neutron number. A detailed comparison with the spectroscopic results of a recent (p, p′) study is made.     

Structural defects in germanium single crystals

The origin and distribution of structural defects (dislocations, small angle grain boundaries, slip lines, polycrystalline inclusions) is studied in large single crystals of germanium applied in manufacturing optical elements.     

Interpretation of far-infrared absorption spectra in germanium

The high resolution far-infrared absorption spectra of free excitons in germanium are analyzed for the first time using a model which accurately includes both the anisotropy of the valence and condition bands and the degeneracy of the valence band. The observed structure is in good agreement with the calculated transitions between the anisotropy split ground state and the various p-like excited states.