Optics and Spectroscopy (v.114, #4)

In an experimental study of excitation of the holmium atom by electrons with an energy of 50 eV, the excitation cross sections are measured for 102 transitions from even levels of Ho I. Radiative transitions to the 4f 116s 2 4 I°13/2,11/2,9/2 levels of the ground state term are considered. Twenty-nine optical excitation functions are recorded in the exciting electron energy range of 0–250 eV. An classification of a number of Ho I lines located in the UV and visible spectral regions is proposed using the known energy levels.

The electron-impact excitation cross sections for 104 transitions from undecuplet levels of the gadolinium atom are measured by the method of extended crossing beams with the exciting electron energy of 30 eV and recording an optical signal of excited atoms from the crossing region. In the electron energy range of 0-200 eV, 16 excitation optical functions are recorded.

Theoretical and FT-IR, FT-Raman studies of nipecotamide and its tautomers, isomers by S̨enay Yurdakul; Nefise Çiǧdem Yas̨ayan (500-508).
The structure, conformers, energies and vibrational spectra of the important nipecotamide molecule have been characterized by FT-IR (mid-IR, far-IR), FT-Raman spectroscopy and by DFT calculations. The structure is optimized by B3LYP/6-311++G(d,p) calculations. All vibrational frequencies assigned in detail with the help of total energy distribution (TED). The calculated vibrational wavenumbers were compared with IR and Ra experimental data. In the most stable tautomer (NT-1), the piperidine ring adopts the chair conformation and the amide group is in the axial orientation and is stabilized by an intramolecular N-H…O hydrogen bond of 4.37 Å.

Raman spectra of alkyl-substituted azaoxa[8]circulenes: DFT calculation and experiment by V. A. Minaeva; B. F. Minaev; G. V. Baryshnikov; M. Pittelkow (509-521).
Raman lines in spectra of recently synthesized azaoxa[8]circulenes have been assigned in detail on the basis of obtained experimental data and B3LYP/6-31G(d) calculations. Particular features of the structure of three azaoxa[8]circulenes have been considered based on data of X-ray structural analysis and DFT calculations. Regularities in changes of the geometric parameters have been found for benzene, furan, pyrrole, and naphthalene rings that occur upon formation of the macroring in comparison with free molecules. Raman spectra of macrorings have been shown to contain a characteristic set of lines the frequencies of which differ from those of analogous lines in Raman spectra of benzene, pyrrole, furan, and naphthalene. Results of quantum-chemical calculations agree well with experimental data with respect to line frequencies and intensities due to recalculation of Raman activities of normal vibrations into intensities of Raman lines.

Enhancement of the quantum efficiency of a fluorescence cesium filter by V. N. Kulyasov; V. B. Shilov; G. M. Ermolaeva; V. G. Krasnov (522-524).
The dependence of the quantum efficiency of fluorescence cesium vapor filters, which allow one to select with a high contrast the desired narrow-band signal against the background of broadband (solar) radiation, is studied. The most important characteristic of such filters, apart from the spectral band, is the quantum efficiency; i.e., the ratio of the number of florescent photons to the number of absorbed photons of excitation. It is experimentally shown that addition of a buffer gas to working cesium atoms can substantially increase the quantum efficiency as compared with that of working atoms in vacuum. The dependence of the quantum efficiency on the characteristic of transitions that are involved in population of atomic levels from which fluorescence occurs, and the processes resulting in an increase in the quantum efficiency of atomic fluorescence filters are considered.

FT-IR, FT-Raman, NMR spectra and DFT simulations of 4-(4-fluoro-phenyl)-1H-imidazole by Y. Erdogdu; D. Manimaran; M. T. Güllüoǧlu; M. Amalanathan; I. Hubert Joe; S̨. Yurdakul (525-536).
The FT-IR, FT-Raman and FT-NMR spectra of the compound 4-(4-Fluoro-phenyl)-1H-imidazole (4-FPI) were recorded and analyzed. Density functional method (B3LYP level with the 6–311G(d, p) and 6–311++G(d, p) and cc-pVQZ as basis sets) has been used to compute optimized geometry, vibrational wavenumbers of the 4-FPI. Only one tautomeric form was found most stable by using DFT/B3LYP. The detailed interpretation of the vibrational spectra was carried out with the aid of total energy distribution following the scaled quantum mechanical force field methodology. Potential Energy Surface scan studies has also been carried out by ab initio calculations with the same basis sets.

The effect of MgO on the optical properties of lithium sodium borate doped with Cu+ ions by Yasser Saleh Mustafa Alajerami; Suhairul Hashim; Wan Muhamad Saridan Wan Hassan; Ahmad Termizi Ramli; Muneer Aziz Saleh (537-543).
The current work presented the photoluminescence (PL) properties of a new glass system, which are reported for the first time. Based on the attractive properties of borate glass, a mixture of boric acid (70-x mol %) modified with lithium (20 mol %) and sodium carbonate (10 mol %) was prepared. The current study illustrated the effect of dopant and co-dopant techniques on the lithium sodium borate (LNB). Firstly, 0.1 mol % of copper ions doped with LNB was excited at 610 nm. The emission spectrum showed two prominent peaks in the violet region (403 and 440 nm). Then, we remarked the effect of adding different concentration of MgO on the optical properties of LNB. The results showed the great effect of magnesium oxide on the PL intensities (enhanced more than two times). Moreover, an obvious shifting has been defined toward the blue region (440 → 475 nm). The up-conversion optical properties were observed in all emission spectra. This enhancement is contributed to the energy transfer from MgO ions to monovalent Cu+ ion. It is well known that magnesium oxide alone generates weak emission intensity, but during this increment the MgO act as an activator (co-doped) for Cu+ ions. Finally, energy band gap, density, ion concentration, molar volume, Polaron radius and inter-nuclear distance all were measured for the current samples. The current samples were subjected to XRD for amorphous confirmation and IR for glass characterization before and after dopants addition. Finally, some of significant physical and optical parameters were also calculated.

Photostimulated luminescence flash: from scientific photography to photonics of nanostructured materials by A. N. Latyshev; O. V. Ovchinnikov; V. G. Klyuev; M. S. Smirnov; D. I. Stasel’ko (544-553).
We have analyzed the possibilities of using the phenomenon of photostimulated luminescence flash for optical diagnosing of energy levels of structural and impurity defects of semiconductor crystals and nanostructures. New data on the spectra of deep localized states associated with adsorbed few-atom clusters Zn n on the surface of ZnS; clusters Cd n , Cu n , and Ag n on the surface of CdS; and clusters Ag n on the surface of AgBr(I) have been presented, as well as results of investigation of photostimulated assembling processes of few-atom clusters on the surface of crystals using this phenomenon. We are the first to show the potential of the luminescence flash technique for studying the mutual arrangement of the levels of dye molecules and the bands of the crystal on the surface of which they are adsorbed, as well as of the spectra of localized states in colloidal CdS semiconductor quantum dots.

The mechanism of sensitized anti-stokes luminescence in crystals with adsorbed dyes by O. V. Ovchinnikov; A. N. Latyshev; M. S. Smirnov; N. V. Kvashnina; T. S. Shatskikh (554-562).
We have analyzed regular features of sensitization processes of crystals AgCl, AgCl0.95I0.05, and Zn0.6Cd0.4S to processes of a low-threshold (10−3–10−4 W/cm2) two-quantum excitation of anti-Stokes luminescence by adsorbed molecules and by J and H aggregates of dyes of different classes. The excitation centers of this luminescence are complex and consist of dye molecules and few-atom silver clusters adsorbed nearby. Luminescence-excitation processes involve stages of photoexcitation of adsorbed dye molecules; resonance transfer of electronic excitation energy to adsorbed atoms and few-atom silver clusters, levels of which lie near the middle of the band gap; and their subsequent photoionization.

We demonstrate the possibility of the existence of eight topologically different types of cones of singular optic axes in crystals having monoclinic and triclinic crystal systems in the presence of birefringence, dichroism, and magneto-optical activity.

Nonlinear optical properties of dibenzoylmethanate boron difluoride crystals by A. G. Mirochnik; E. V. Fedorenko; I. G. Nagorny; A. N. Pavlov (568-569).
Nonlinear optical properties of dibenzoylmethanate boron difluoride crystals have been discovered. The optical properties of bulk crystals and microcrystals are different. The bands observed in the luminescence spectrum of the bulk crystals can be interpreted as follows: the narrow band at 530 nm is ascribed to second harmonic generation; the wide band at 460 nm is caused by multiphoton excitation processes. A specific difference in nonlinear optical properties of the bulk crystals and microcrystals is the absence of the band related to the multiphoton excitation processes in the luminescence spectrum of microcrystals. Therefore, in the case of dibenzoylmethanate boron difluoride crystals, a size dependence of not only luminescent, but also of nonlinear optical properties, is discovered for the first time, which is promising for the development of new optical materials.

Kinetics of photoreactions with participation of molecular oxygen in Langmuir-Blodgett films by A. K. Aimukhanov; N. Kh. Ibrayev; M. G. Kucherenko; T. M. Chmereva (570-576).
The influence of molecular oxygen on the luminescence of organic molecules (dyes and aromatic hydrocarbons) in Langmuir-Blodgett films is studied. Experimental luminescence kinetics curves are compared with theoretical curves calculated in terms of different mathematical models. It is shown that the best agreement with experiment is achieved using a model that takes into account the frontal diffusion of excited oxygen molecules to the interphase surface.

A study of the precipitation mechanism in GK transformer oil by O. A. Turanova; A. E. Vandyukov; V. K. Kozlov; A. N. Turanov (577-580).
The room-temperature IR spectra of fresh, used, and aged under model conditions GK trans-former oil, as well as of its residue, are recorded, interpreted, and compared. Analysis of the data obtained confirms the presence of small amounts of aromatic compounds in these samples and shows that the fraction of aromatic and oxidized compounds in transformer oil increases during exploitation. Based on this, a new precipitation mechanism in transformer oil is proposed.

Specific features of charge-transfer states and charge-transfer transitions of the O2p → Cr3d type in octahedral complexes (CrO6)9− have been considered in the cluster approximation. Reduced matrix elements of the electric-dipole moment operator on many-electron wave functions, which are the initial and final states for charge-transfer transitions, are calculated. The results are parameterized, and the relative intensities of different allowed charge-transfer transitions in the absence of mixing of different charge-transfer configurations with identical symmetry are calculated. This mixing is taken into account within the Tanabe-Sugano theory, and the true energies and intensities of many-electron charge-transfer transitions are obtained. The Coulomb interaction between 2p electrons of O2− ligands and 3d electrons of the central Cr3+ ion in (CrO6)9− cluster is considered. The influence of this interaction on the optical spectra is found to be insignificant. Simulation of the optical spectra of chromium oxides has shown the presence of a band of complex charge-transfer transitions composed of 33 lines with a total width of about 8 eV. The model spectrum is in adequate agreement with the experimental data, which indicates limited applicability of the widespread view that charge-transfer transition spectra have a simple structure.

We have calculated the vibronic absorption and fluorescence spectra of the first (1 L b ) and second (1 L a ) electronic transitions of indole in the isolated state and aqueous solution. The vibrational structure of the absorption and fluorescence spectra has been interpreted. The influence of the aqueous solution on the vibronic spectra has been shown.

Optical properties of a stack of layers of a cholesteric liquid crystal and an isotropic medium by M. Z. Harutyunyan; A. H. Gevorgyan; G. K. Matinyan (601-613).
Optical properties of a stack consisting of layers of a cholesteric liquid crystal (CLC) and an isotropic medium are investigated. The problem is solved using the modified Ambartsumyan layer-summation method. Particular features of reflectance spectra of this system are studied. It is shown that, in contrast to a single CLC layer, this system exhibits multiple photonic band gaps. There are two types of photonic band gaps: selective and nonselective with respect to polarization of the incident light. It is shown that eigenpolarizations in the system generally coincide with quasi-orthogonal quasi-circular polarizations, except for regions that are selective with respect to polarization of the diffractive reflection. It is shown that, for an even number of layers, the system under consideration is nonreciprocal and can function as an optical diode. The influence of thickness of CLC sublayers, angle of incidence, local dielectric anisotropy of CLC layers, refractive indices and thicknesses of layers of an isotropic media on reflectance spectra and other optical characteristics of the system is investigated.

Studies of higher-order nonlinearities in plasma plumes by the method of higher-harmonic generation (HHG) upon laser ablation of different materials by pulses with a repetition rate of 1 kHz are reviewed. It is shown that an increase in the pulse repetition rate compared to the previous works on HHG in plasma using lasers with a pulse repetition rate of 10 KHz considerably increases the average power of converted radiation in the far-ultraviolet (FUV) region. The review considers the results of works on the interference of quantum trajectories of accelerated electrons, two-color pumping, HHG in graphite plasma, HHG in gases compared to HHG in plasma plumes, resonant enhancement of harmonics, and stabilization of the output parameters of radiation converted in plasma. It is shown that the new methods of optimization of the HHG process considerably increase the potential of the use of coherent FUV radiation owing to the improvement of some characteristics of harmonics in plasma generated by pulses with a high repetition rate.

The effect of the size of particles on optical and electrooptical properties of colloids by V. V. Vojtylov; M. P. Petrov; A. A. Spartakov; A. A. Trusov (630-638).
We have considered optical and electrooptical properties of disperse systems that contain particles with different optical characteristics, sizes, and shapes. Our investigations of the refractive index of a series of disperse systems have shown that, if the particle size does not exceed a few tens of nanometers, the refractive index does not depend on the particle concentration and is equal to the refractive index of a molecular medium that surrounds particles. We have shown that, in an external electric field, systems with these particles almost do not possess birefringence but possess dichroism. Our investigations of systems with a low concentration of particles allowed us to find that the intensity of light transmitted through a Kerr cell that is filled with colloidal particles with a size comparable with the wavelength and that is placed between crossed polarizers varies proportionally to the squared dichroism induced in the colloid by the external field. Linearly polarized light transmitted through this cell in the electric field remains to be linearly polarized, but its plane of polarization rotates by an angle the tangent of which is proportional to the dichroism of the colloid. We propose a method for determining the contributions from birefringence and dichroism to the observed electrooptical effects.

In present paper the reflectivity of binary and ternary one-dimensional plasma photonic crystals for obliquely incident electromagnetic waves are studied. The reflectivity is derived using transfer matrix method and solving Maxwell’s equations by employing the continuity conditions on the electric fields and its derivatives. Our analysis shows that the perfect reflection bands get enhanced in the ternary 1D-PPCs compared to the binary 1D-PPCs. Also the ternary 1D-PPCs provide an additional degree of freedom to control the perfect reflection bands.