Influence of temperature on phosphorescence spectra of Pd-porphine in Shpol’skii matrices

We have studied the temperature dependence of the radiative deactivation of the Pd-porphine triplet states in Shpol’skii matrices in the temperature range 1.2–210 K. A substantial transformation of the phosphorescence spectra is observed as the temperature increases and is due to the inclusion of thermally activated Pd-porphine states in the radiative deactivation processes. The activation energy E_a of these Pd-porphine states is measured in matrices of n-octane and n-nonane. The splitting of the lowest quasidegenerate triplet state ΔE(T₂−T₁) is determined for planar and distorted conformations of the Pd-porphine macrocycle in the n-octane matrix as 40 and 57 cm⁻¹, respectively. The ability to use the temperature dependence of the phosphorescence properties of Pd-porphine to fabricate molecular thermometers for the low-temperature range is analyzed. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 460–464, July–August, 2007.     

Calculation of polarization aberrations by the method of polarization-wave matrices

The technique of calculation of polarization aberrations with the help of the method of polarizationwave matrices is proposed. Radiation is represented as a coherent set of the Hermitian-Gaussian modes with a certain amplitude, phase, and polarization state; the longitudinal component of the field is also taken into account. Polarization aberrations are considered as a set of spurious modes. Polarization aberrations caused by a cylindrical converging lens and a diaphragm are studied.     

Growth and characterisation of Eu doped GaN thin films

We have studied the optical properties of Eu doped GaN thin films. We have grown high quality Eu doped GaN thin films by using Gas Source Molecular Beam Epitaxy (GSMBE), with 1.4% Eu concentration. The Full Width at Half Maximum (FWHM) of the X-ray diffraction in an omega scan was found to be 288 arcsecs. Low Eu concentration (0.08%) doped GaN thin films were grown, where Eu-related photoluminescence at 622 and 613 nm was detected using above band-gap excitation at 2 K. For high Eu concentration of 30% GaN:Eu crystal photoluminescence (PL) and cathodoluminescence (CL) spectra show strong and intense transitions at 622 and 664 nm, but also at 593 nm for CL spectra, with a similar transition observed from the low Eu concentration sample.     

Acoustooptic cells with nonuniform length of light-sound interaction

Diffraction of light by acoustic waves that are generated in the acoustooptic cells of piezoelectric transducers with complex geometry is studied. The diffraction by acoustic beams with triangular, quadrangular (rhombic), hexagonal, etc., cross sections, when the lengths of light-sound interaction in the cross-sectional area of the light beam are different, is considered in the plane wave approximation. The difference in the length of interaction affects the instrument function of acoustooptic devices and provides the suppression of the side lobes in their transmission function. The advantages of using cells with complex-geometry transducers in tunable acoustooptic filters that are incorporated into fiber-optic communication lines with wavelength-division multiplexing (WDM) are discussed.     

Eigenvalues of the antiplane-shear crack problem for a power-law material

This paper discusses the problem of finding the eigenvalue spectrum in determining the stress and strain fields at the tip of an antiplane-shear crack in a power-law material. It is shown that the perturbation method provides an analytical dependence of the eigenvalue on the material nonlinearity parameter and the eigenvalue of the linear problem. Thus, it is possible to find the entire spectrum of eigenvalues and not only the eigenvalue of the Hutchinson-Rice-Rosengren problem. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 1, pp. 173–180, January–February, 2008.     

MgO films grown on yttria-stabilized zirconia by molecular beam epitaxy

MgO films were grown on (0 0 1) yttria-stabilized zirconia (YSZ) substrates by molecular beam epitaxy (MBE). The crystalline structures of these films were investigated using X-ray diffraction and transmission electron microscopy. Growth temperature was varied from 350 to 550 °C, with crystalline quality being improved at higher temperatures. The MgO films had a domain structure: (1 1 1)[1 1 2¯]_MgO(0 0 1)[1 0 0]_YSZ with four twin variants related by a 90° in-plane rotation about the [1 1 1]_MgO axis. The observed epitaxial orientation was compared to previous reports of films grown by pulsed laser deposition and sputtering and explained as resulting in the lowest interface energy.     

Circular dichroism spectra of langasite family crystals in the range of electronic transitions of structure defects

The absorption and circular dichroism spectra of langasite family crystals are studied. Wide bands in the range of 285–500 nm that are related to the structure lattice defects are found. For all the crystals, these bands are in approximately the same spectral region, have identical structures, and can be attributed to one type of defects formed by cation vacancies and excess oxygen atoms in the optically active positions.     

Specific features of the formation of submicron inclusion in Ti:sapphire

Specific features of the formation of submicron (70–300 nm) inclusions in Ti:sapphire (Al₂O₃:Ti) grown in a carbon-containing medium have been investigated. These inclusions are caused by deviation from the melt stoichiometry and are formed during the melt-crystal phase transition. These defects are submicropores containing excess aluminum and its suboxides; they can be destroyed by thermal loading of a crystal.     

Numerical study of the influence of boundary conditions on the dynamic behavior of a cylindrical shell conveying a fluid

We consider a finite element algorithm intended to study the dynamic behavior of an elastic cylindrical shell filled with an immovable or flowing fluid. To describe the fluid, we use the perturbed velocity potential whose equations with the corresponding boundary conditions are solved by the Bubnov-Galerkin method. To describe the shell, we use the variation principle, which includes the linearized Bernoulli equation for calculating the hydrodynamic pressure acting on the shell on the side of the fluid. Solving the problem is reduced to calculating and analyzing the eigenvalues of the coupled system of equations obtained as a result of combining the equations for the perturbed velocity potential and the shell displacements. We consider several test problems in which, along with the comparison of the computational results with the earlier published experimental, analytic, and numerical data, we also study the dynamic behavior of the “shell-fluid” system for various boundary conditions for the perturbed velocity potential.