Vol 125, No 2 (2018)

The energy levels and probabilities of radiative transitions to the ground state of Ni-like ions with Z = 36–51 are calculated. The energies of the upper working level 3d_3/24f_5/2 [J = 1] and the lower working level 3d_3/24d_3/2 [J = 1] of self-photo-pumped X-ray lasers along the sequence of Ni-like ions are studied. It is shown that, at the points of intersection of levels of the same parity, a strong interaction of these levels takes place, which leads to a redistribution of the oscillator strengths of the radiative transitions from these levels. Near the intersection points, the emission spectra change abruptly with variation in the nuclear charge Z.

The kinetics of energy exchange between the plasmonic and excitonic subsystems in a “metal–dielectric–molecular layer” is studied for a planar composite nanostructure with a strong exciton–plasmon interaction. It is shown that the time dependence of the energy transfer between the components of the system has the character of damped oscillations, which depend on the prepared initial state, a number of relaxation parameters, the Rabi frequency, and the detuning from resonance.

Spectra of Eu³⁺ in various dielectric matrices (Gd₂O₃:Eu³⁺, Y₂O₃:Eu³⁺, Eu₂O₃, and mSiO₂/Gd₂O₃:Eu³⁺ mesoporous particles) are studied by local cathodoluminescence. The results allowed identification of the local environment of Er³⁺ ions in amorphous samples and detection of the monoclinic Eu₂O₃ phase impurity in samples with yttrium oxide. The cathodoluminescence spectra of chemically pure Y₂O₃, Eu₂O₃, and Gd₂O₃ are recorded. Conclusions about the structural features of the materials are made and confirmed by other methods (XRD and EPMA).

The interaction of porous silicon (PS) with aqueous solutions of Fe(NO₃)₃ with different molar (M) concentrations causes introduction of iron ions into silicon pores (PS–Fe), formation of adsorbed iron coatings with different thicknesses, and an increase in the stability of PS layers, which is important for development of device structures based of PS. To treat PS layers with solutions by the immersion method, it is necessary to determine how this affects the spectral composition and intensity of photoluminescence (PL), as well as the kinetics of PL changes during long storage under atmospheric conditions. Upon treatment of freshly prepared PS by immersion into in a Fe(NO₃)₃ aqueous solution, it was found that, after short-term storage (up to 5 days) of the PS samples, the PL intensity increases by 7.5 and 3–3.6 times at low (0.2 M) and high (0.7–0.8 M) concentrations of Fe(NO₃)₃, respectively, compared to the PL intensity of an untreated PS layer. After long-term storage (4 months), the PL intensity of PS–Fe samples with concentrations of 0.1–0.2 and 0.7–0.8 M was observed to considerably increase (by 8–18 times) with unchanged position of the PL peak with respect to untreated PS. However, at the Fe(NO₃)₃ concentration of 0.3 М, the PL intensity decreases and the PL peak shifts to the blue, which is explained by incomplete coverage of the PS surface by an adsorbed iron layer. The kinetics of PL spectra during long-term storage is analyzed, and a model is proposed to explain the PL intensity and spectral composition.

Electronic-excitation energy transfer between molecules of Coumarin 7 (donor) and Rhodamine B (acceptor) have been experimentally investigated in one-dimensional photonic crystals based on oxidized mesoporous silicon and in a similar matrix, which does not possess the properties of a photonic crystal. The efficiencies of excitation transfer between donor and acceptor molecules have been determined based on the donor-fluorescence quenching and sensitized acceptor luminescence. It is established that the efficiency of electronic-excitation energy transfer in a photonic crystal increases in comparison with that for porous silicon.

Polarization studies of the vibrational spectra of clusters (H₂O)_n in samples of single-crystal fluorapatite of different deposits were carried out by infrared (IR) spectroscopy and Raman spectroscopy. The IR and Raman spectra were measured for two orthogonal directions of the external excitation field: parallel and perpendicular to the c-channels in fluorapatite single crystals. Interpretation of the interaction of the external electromagnetic field with clusters of water situated in microvoids and microcracks of the crystal with the structural groups of F…HO of apatite is given in the framework of the dipole–dipole approximation. This interaction has an induction–resonance character (IR spectroscopy) caused by the transfer of vibrational excitation from the F…HO groups to (H₂O)_n clusters. In the case of Raman spectroscopy, the induction character of the excitation of (H₂O)_n clusters takes place due to the transfer of electron excitation from the F…HO groups.

Transient radiation of a charged particle in a waveguide with modulated anisotropic magnetodielectric filling is considered. It is assumed that the particle moves with a constant velocity perpendicularly to the axis of the waveguide the filling of which is periodically modulated by the harmonic law. Wave equations for the transverse electric (TE) and transverse magnetic (TM) fields in the waveguide have been obtained. Analytical expressions have been obtained for fields in the waveguide in the first approximation by small modulation indices of waveguide filling. Energies of transient radiation of a charged particle have been calculated in the region of weak (nonresonance) interaction between the radiation and modulation waves, in particular, in the case of a rectangular waveguide. It has been shown that radiation energies at the zero harmonic in the region of weak interaction do not depend on the modulation indices and are proportional to the modulation indices in the first power at the plus and minus first harmonics. The mechanism of the appearance of Cherenkov radiation has been analyzed.

Results of investigation of 1550 nm range stripe semiconductor lasers fabricated from heterostructures with different designs of the gain medium are presented. It is shown that the proposed designs of the gain medium allow obtaining the effective lasing at high level of total optical losses, comparable with the typical optical losses in the vertical-cavity surface-emitting lasers. The evaluation of modal gain in different types of the gain mediummade it possible to estimate the possible frequencies of the small-signal modulation of vertically emitting lasers and proposed the ways to increase them up to 20 GHz or more.

Extinction spectra, effective sizes, and aggregate stability of silver nanoparticles and nanocomplexes of silver nanoparticles with chymotrypsin obtained by the reactions of chemical reduction of silver nitrate using sodium borohydride as a reducing agent are studied. It is shown that silver nanoparticles obtained in the absence of chymotrypsin are aggregatively stable only at pH values immediately after synthesis. The placement of the synthesized silver nanoparticles in buffer solutions with pH values from 3.0 to 12.0 resulted in the appearance of a wide absorption band in the visible region of the spectrum, which is due to the agglomeration of silver nanoparticles, which appears to be the result of the destruction of the double electric layer formed by the ions making up sodium borohydride. The presence of chymotrypsin in the reaction medium resulted in significant spectral changes. Unlike silver nanoparticles synthesized in the absence of chymotrypsin, for nanocomplexes of silver nanoparticles with chymotrypsin with a change in pH, the shape of the extinction spectra and the position of the surface plasmon resonance band were preserved, while nanocomplexes of silver nanoparticles with chymotrypsin retained the aggregative stability in solutions in the pH range from 3.0 to 12.0 within a month. The observed stabilization effect of silver nanoparticles over a wide pH range induced by the presence of chymotrypsin in the reaction medium can be used further to develop methods for immobilizing enzymes on nanoparticles of biogenic elements and for creating polyfunctional pharmaceuticals, in which the components of nanocomplexes have different biological activity.

Data on quantum yields and photoluminescence decay times of quantum dots have been collected. Photoprocesses that occur in quantum dots are compared with photoprocesses occurring in complex organic molecules in the condensed phase. The review consists of the introduction, three parts, and conclusions. The first two parts are devoted to quantum dots that are formed by indirect-gap semiconductors. The first part is devoted to data on the photoluminescence quantum yields and decay times of carbon quantum dots, and Table 1 presents selected values and short comments to these data. Table 2 of the same part presents data on fast relaxation processes in the same objects. In the second part, Tables 3 and 4, as well as the following text, contain similar information about silicon quantum dots. Data on photoprocesses in quantum dots formed by direct-gap semiconductors are collected in the third part. Data on the photoluminescence yields, decay times, and relaxation processes are listed in Tables 5 and 6. Particular attention in the present review is given to the effect that a change in the frequency of vibrations in the environment of a quantum dot has on the photoluminescence yields and the rate of relaxation processes between electronic levels in bands, which indicates that the inductive resonance mechanism of nonradiative transitions is applicable to these systems.

The effect of pretilt and twisted angle on twisted nematic liquid crystal filter (TNLCF) is studied theoretically and experimentally in this paper, based on the birefringence and distortion characteristic of twisted nematic liquid crystal, the output performance of TNLCF has been analyzed through numerical simulation firstly, then the corresponding experiment results verify the correctness of the simulation results, which show that the output performance of TNLCF is indeed related to pretilt angle and twisted angle of liquid crystal–with the increasing of the twisted angle the central wavelength of TNLCF will shift to the long wavelength, with the increasing of pretilt angle for the top glass substrate and the decreasing of pretilt angle for the bottom glass substrate the central wavelength of TNLCF will shift to the short wavelength, and if the pretilt angle of the bottom glass substrate is increased and the pretilt angle of the top glass substrate is reduced at the same time in some certain value or otherwise the shift trend of the central wavelength will be not evident. These results will offer an important reference value for the design and application of TNLCF as we believe.

The causes of the occurrence and the method of the elimination of defects of non-bridging oxygen in multimode fluorosilicate optical fibers prepared by the modified method of chemical vapor deposition are considered. The solution is the use of support tubes obtained by quartz surfacing in a hydrogen atmosphere. In this case, there is no absorption band in a range of 630 nm caused by nonbridging oxygen in the spectrum of optical losses of gradient fluorosilicate optical fibers of W-type. Attenuation in a visible spectrum range is mainly determined by the level of Rayleigh scattering and the mode dispersions at a wavelength of 342 and 683 nm are 1.2 ± 0.1 and 0.7 ± 0.2 ps/m, respectively.

Spectra of optical density of granulated 2-nm-thick gold films deposited on the surface of thin films of amorphous hydrogenated carbon (a-C:H) on quartz substrates are investigated. A shift of the peak corresponding to the localized surface plasmon resonance toward the shorter wavelengths by 32 nm upon an increase in the optical bandgap of the a-C:H films from 0.8 to 2.4 eV is demonstrated. Simultaneously, an increase in intensity and narrowing of the plasmon-resonance band in spectra of gold nanostructures is observed. This fact indicates that formation of the granulated gold films on the surface of a-C:H films depends on the specific structural properties of the latter.

In this study, we measured the spectral-kinetic characteristics of ignition of dustlike (pulverized) coal particles with a particle size of ≤100 μm using an yttrium-aluminum garnet laser with an admixture of neodymium operating in the free-running mode (120 μs). We discovered three stages of the process, each of which has a threshold character. During the laser pulse in the energy density range of 0.3–1.5 J/cm², a rapid heating of the sample surface to 3000 K occurs due to the absorption of laser energy and initiation of a chemical reaction in the coal particles. In the energy density range of 1.6–2.1 J/cm², the yield and ignition of volatile matter above the sample surface are observed in the time interval of 0.5–2 ms. In the emission spectra of the flame, we are able to distinguish bands associated with the combustion of volatile matter including the CO flame and the emission of excited H₂O and H₂ molecules. At H > 2 J/cm², ignition and burning of the coke residue takes place in a time interval of 10–100 ms. Its emission spectrum corresponds to the emission spectrum of a black body at 1800 K.