Том 122, № 3 (2017)

It is shown that laser generation is possible in principle upon coherent excitation according to the V-scheme of the (1s2p)³P_j levels with j = 1, 2 of a helium atom from the (1s2s)³S₁ level of the same atom when the latter level is, in turn, populated by electron or proton impact.

The one-photon transition probabilities in hydrogen-like ions are calculated for nuclear charge numbers in the range 1 ≤ Z ≤ 100. The calculations are performed in the framework of the relativistic Dirac’s theory for the states with the principal quantum numbers n = 2,3, 4. The finite nuclear size effect is taken into account. The role of the quantum electrodynamics (QED) and nuclear recoil corrections is also considered.

The optical properties of gold nanoparticles in a transparent matrix are studied at temperatures from 300 to 1000 K within the spectral range from 450 nm to 1.5 μm. It is shown that, in the case of small nanoparticles and short wavelengths in the plasmon resonance band, an increase in temperature leads to a decrease in the absorption efficiency factor. The light absorption efficiency factor of gold nanoparticles with a radius exceeding 40 nm increases with increasing temperature in the entire spectral range studied. The single scattering efficiency factor always decreases with increasing temperature. The effects observed are related to a change in the refractive indices of gold and the matrix with comparable contributions. It is shown that results of calculations agree qualitatively with available experimental data. The results are necessary to optimize the composition of the actuators, including gold nanoparticles, in the transparent matrices.

The possibility of double spectral conversion of UV radiation from the spectral range of 240–280 nm to the visible spectral region using luminescent glasses and fibers with antimony ions and molecular silver clusters is shown. Planar and fiber prototypes of UV radiation dosimeters are tested. It is shown that the sensitivities of dosimeter of the first and second types are 1400 and 360 mV/W/m², respectively.

The results of the spectroscopic NMR (¹H, ¹³C, and ¹⁹⁵Pt), infrared, optical, and voltammetric characteristics of the mixed-ligand complexes of Pt(II) and Ir(III) with metalated 2-phenylbenzothiazole and tert-butylisocyanide (tBuNC), acetonitrile (AN), ethylenediamine (En), O-ethyldithiocarbamate (Exn^–), and diethyldithiocarbamate (Dtc–) ions are presented. It is demonstrated that the change in donor–acceptor interaction of ligands tBuNC, AN, En, Exn^–, and Dtc^– with metal leads to an increase in the energy of the highest occupied molecular orbital of the complexes and is accompanied by a shift of the cathode potential of the metal-centered oxidation, a bathochromic shift of the spin-allowed and spin-forbidden metal-tocyclometalated ligand optical charge transfer transitions, and an increase the degree of mixing of the ¹MLCT and triplet intraligand states, responsible for the phosphorescence of the complexes.

The dispersion of the electro-optical effect in polydisperse hydrosols of diamond is studied in the external field frequency ranging from 10 Hz to 2.5 MHz. The conservative dichroism, which is determined by the difference in the turbidity constants for light polarized along and perpendicular to the particle-orienting field, is chosen as the electro-optic effect. The dispersion dependences of the dichroism are determined and used to calculate the dispersion of the average values of the polarizability anisotropy of the diamond particles. The influence of the concentration of monovalent ions in an aqueous KCl solution on these dispersion dependences is studied. The experimental dependences of the dispersion are compared with the theoretical ones within the model of the polarizability of the colloidal particles which takes into account the polarizability of the diffuse part of their double electric layer.

The spectroscopic and photophysical properties of the biologically important plant antioxidant quercetin in organic solvents, polymer films of polyvinyl alcohol, and a buffer solution at pH 7.0 are studied by stationary luminescence and femtosecond laser spectroscopy at room temperature and 77 K. The large magnitude of the dipole moment of the quercetin molecule in the excited Franck–Condon state μ_e^FC= 52.8 C m indicates the dipolar nature of quercetin in this excited state. The transient induced absorption spectra S₁→S_n in all solvents are characterized by a short-wave band at λ_abs^max = 460 nm with exponential decay times in the range of 10.0–20.0 ps. In the entire spectral range at times of >100 ps, no residual induced absorption was observed that could be attributed to the triplet–triplet transitions Т₁ → Т_k in quercetin. In polar solvents, two-band fluorescence was also recorded at room temperature, which is due to the luminescence of the initial enol form of quercetin (~415 nm) and its keto form with a transferred proton (550 nm). The short-wave band is absent in nonpolar 2-methyltetrahydrofuran (2-MTHF). The spectra of fluorescence and fluorescence excitation exhibit a low dependence on the wavelength of excitation and detection, which may be related to the solvation and conformational changes in the quercetin molecule. Decreasing the temperature of a glassy-like freezing quercetin solution in ethanol and 2-MTHF to 77 K leads to a strong increase in the intensity (by a factor of ~100) of both bands. The energy circuits for the proton transfer process are proposed depending on the polarity of the medium. The main channel for the exchange of electronic excitation energy in the quercetin molecule at room temperature is the internal conversion S₁ ⇝ S₀, induced by the state with a proton transfer.

A composite polymeric material based on polymethylmethacrylate (PMMA) with embedded electro- optical (EO) chromophore DR13 is designed. Irradiation with electromagnetic radiation in the visible range leads to a bleaching of the composite and its refractive index n decreases due to the irreversible photodestruction of the chromophore. Changes in the absorption spectrum and refractive index of the composite with the irradiation time are measured. It is shown that the change in n depends on the concentration of DR13 in the polymer matrix and can reach a value of Δn = 0.034 in the telecommunication C-range near a wavelength of 1.55 μm. The rate of bleaching depends on the wavelength of the actinic light and reaches its maximum when the wavelength is near the maximum of chromophore absorption. With the use of the photobleaching method and the PMMA/DR13 composite, channel waveguides and the other elements of the integrated optical devices are fabricated, including waveguide splitters, directional couplers, and Mach–Zehnder interferometers. This simple one-step method does not involve the removal of polymer material by liquidphase or reactive ion etching.

We have proposed an ellipsoidal model (ElM) for small nonspherical particles, i.e., we have proposed a method to construct “effective” ellipsoids the light scattering properties of which are similar to those of original particles. It has been shown that the semiaxes of a model ellipsoid should be determined from the requirement of equality of the volumes of particles, as well as of the equality of the ratios of their maximal longitudinal and transverse dimensions. Along with the ElM, the uniform internal field approximation (UFA) has also been considered, which is the first approximation in terms of the rigorous ЕВСМ solution of the electrostatic problem. In order to analyze the applicability of the ElM and UFA approximate approaches, rigorous methods for solving the problem of light scattering have been used, such as the discrete dipole approximation (DDA) and the SVM. The comparison of results of numerical calculations for parallelepipeds, finite circular cylinders and cones, Chebyshev particles and pseudospheroids has shown that the relative errors of calculations of the particle polarizability using ElM approximate formulas do not exceed 1–5%, while, for the absorption and scattering cross sections, they are roughly twice as large, since they depend on the squared polarizability module. As a rule, the ElM is preferable to the uniform field approximation, which is advantageous only in the case of a circular cylinder with close longitudinal and transverse dimensions.

Spectral-kinetic characteristics of luminescence of tetranitropentaeritrite with inclusions of iron nanoparticles upon an explosion induced by laser pulses are measured with high temporal resolution. It is shown that the luminescence occurring during exposure to the laser pulse is a result of initiating a chemical reaction in tetranitropentaeritrite and is chemiluminescence. The glow is presumably associated with the excited nitrogen dioxide, NO₂, which is formed by the rupture of O–NO₂ bond in the tetranitropentaeritrite molecule.