卷 125, 编号 4 (2018)

Using modern methods of theoretical atomic spectroscopy, it is possible to perform calculations of atomic systems which are necessary in solving practical problems in various areas of physics, in particular, in astrophysics. For this purpose, different purely theoretical (ab initio) have been used, including methods developed recently. In calculations of atomic systems, along with the ab initio methods, different variants of the semiempirical method are also employed.

Using high-precision nonempirical methods of modern quantum chemistry, the effect of the weak relativistic interactions on the potential energy and the permanent dipole moment of the ground electronic state of the CO molecule is studied. The relativistic energy is calculated by the following three optional methods: within the first-order perturbation theory using the Cowan–Griffin operator containing the sum of the mass-velocity and Darwin corrections, within the framework of the approximate Douglas–Kroll–Hess scalar Hamiltonian, and the most rigid “four-component” relativistic Dirac–Coulomb–Gaunt Hamiltonian. The relativistic correction obtained by different methods agrees within a few percents and equals about 55–60 cm^–1 in the region of an equilibrium internuclear distance of \({{R}_{e}} = 1.128\) Å. The addition of the relativistic correction decreases the equilibrium bond length by about 0.0002 Å. The magnitude of the Lamb shift estimated by the semiempirical scaling of the one-electron Darwin’s term does not exceed several inverse centimeters near \({{R}_{e}}\). The relativistic correction to the dipole moment function is in the range from –0.001 to +0.003 D, which does not exceed 1% of the nonrelativistic component of the dipole moment.

Results of investigation of the phototransformation dynamics of chromone molecules by means of a transient-state spectroscopy are presented. Changes in the spectrum of the optical density of chromone compounds dissolved in toluene in the process of their phototransformation are obtained on a time scale ranging from several hundred femtoseconds to several hundred picoseconds. Relaxation of an induced absorption spectrum is described by a biexponential function with characteristic time constants on the order of several picoseconds and several nanoseconds. A scheme of the phototransformation dynamics of chromone molecules corresponding to the observed dynamics of absorption spectra is proposed.

Visualization of IR radiation of a Tm:YLF laser with a wavelength of 1908 nm in 53ZrF₄–20BaF₂–3LaF₃–1HoF₃–3AlF₃–20NaF (mol %) ceramic samples is studied. The luminescence spectra of Но³⁺-doped ZBLAN ceramics exhibit bands in the regions of 540, 650, and 900 nm, which correspond to the ⁵S₂ → ⁵I₈, ⁵F₅ → ⁵I₈, and ⁵I₅ → ⁵I₈ transitions, the red band (650 nm) being most intense. The population of the upper levels of these transitions can be explained using the cascade excitation mechanism. A visualization model is developed based on balance equations for populations of the upper energy states of Но³⁺ ions. The population distributions are numerically estimated as functions of the excitation intensity. The obtained time dependences of the populations of the ⁵S₂ and ⁵F₅ states correlate with the experimental time dependences of the luminescence intensity at the ⁵S₂ → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions upon pulsed excitation. The threshold power density of a Tm:YLF laser at which luminescence of the ceramic samples was observed was ~2 W/cm².

The results of a study of the optical properties of conducting polymers, namely, derivatives of poly-N-epoxypropylcarbazole (PEPC) with heavy atoms, are presented. It is shown that a heavy atom in the structure of a polymer molecule leads to bathochromic shifts in the absorption, fluorescence, and phosphorescence spectra. This is a consequence of a decrease in the energy of the electron levels due to a change in the electron density distribution over the π-electron system in the chromophores of 2IPEPC and 3BrPEPC. Two bands can be distinguished in the fluorescence spectra of PEPC with heavy atoms, just as in the parent polymer. The emission band with a maximum at 380 nm belongs to the monomer luminescent centers and the long-wavelength emission with a maximum at about 420 nm to the polymer excimers. A heavy atom changes the ratio of the intensities of the monomer and excimer bands. The fluorescence lifetimes also decrease in the presence of a heavy atom. Quantum-chemical estimation of the intramolecular transition constants has shown that the probability of the singlet–triplet intercombination conversion in the halogen-containing PEPCs is higher in PEPC. This leads to a markedly stronger phosphorescence of the iodine and bromine-containing polymers and a shorter luminescence lifetime. The obtained results can be used in the development of composite materials based on photoconductive polymers for photovoltaics and optoelectronics.

Mechanofluorochromism and thermofluorochromism of boron difluoride 3-methylamino-1,3-diphenyl-2-propen-1-one have been detected. Upon grinding of crystals, they exhibit a significant change in their excitation spectra. A dependence of the luminescence spectrum on the wavelength of the exciting light has been found, which indicates the occurrence of luminescence centers of two different structures. Upon heating of a grinding sample, a further evolution of its luminescence and excitation spectra has been observed. The mechanism of the observed effects has been proposed to be associated with dissociation and formation of J-aggregates.

Microrod arrays of zinc oxide with copper have been grown by chemical vapor deposition on single-crystal sapphire substrates preliminarily covered with a nanoscale copper layer. The presence of copper (about 0.3%) in zinc-oxide microrods has been experimentally shown to increase the photoluminescence intensity of the ZnO microcrystal arrays, reduce the lasing threshold, and lead to a small (by ~2.5 nm) blue shift of the radiation intensity peak of the ZnO microcrystals. It is shown that the laser-radiation character depends on the morphology of the ZnO microrod arrays.

Upconversion luminescence of fluoride phosphors SrF₂:Er,Yb co-precipitated from aqueous solutions is studied. Under excitation of Er³⁺ ions to the ⁴I_13/2 level, upconversion luminescence spectra are recorded in the visible and near-IR spectral regions, which correspond to the ⁴G_11/2 → ⁴I_15/2, ²H_9/2 → ⁴I_15/2, ⁴F_5/2 → ⁴I_15/2, ⁴F_7/2 → ⁴I_15/2, ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2, ⁴F_9/2 → ⁴I_15/2, ⁴I_9/2 → ⁴I_15/2, and ⁴I_11/2 → ⁴I_15/2, electronic transitions of Er³⁺ ions and to the ²F_5/2 → ²F_7/2 transition of Yb³⁺. The absolute quantum yields of visible upconversion luminescence under excitation in the region of 1.5 μm are determined for SrF₂:Er,Yb phosphors with different concentrations of Er³⁺ and Yb³⁺ ions and analyzed comparatively with the corresponding values for SrF₂:Er phosphor. A study of chromaticity coordinates showed that the yellow-green upconversion luminescence of SrF₂:Er,Yb phosphors is characterized by color temperatures of 3037–3526 K at an incident power density of 850 W/cm².

The resonance linear transformation of the integral mutually orthogonal polarization modes has been calculated for the typical parameters of coiled optical spun fibers for four cases. In the first three cases, the spatial periods (lengths) of the polarization beats of the unperturbed linear birefringence caused by the winding of the spun fiber to the coil, unperturbed linear birefringence and circular birefringence associated with the twisting of the spun fiber pairwise coincide. It is shown that, in all three cases, pronounced resonant phenomena occur, which consist in periodic changes in the ellipticity of the intrinsic polarization modes of spun fibers. In this case, the polarization of integral eigenmodes changes from linear to right-circular, then to linear, then to left-circular, then again to linear. In all three cases, there are some qualitative differences. It is shown that, at certain values of the length, the spun fiber loses strong birefringence. The case is also considered when all three indicated lengths of polarization beats are equal to each other. It is shown that in this case the evolution of the integral polarization modes differs markedly from the three previous cases. The evolution of the state of the radiation polarization on the length of spun fibers with its representation on the Poincare sphere is calculated. An optomechanical analogy of the resonant linear transformation of orthogonal polarization modes in spun fibers is presented.

The photoanisotropic properties of polarization sensitive luminescent media applied in holography based on bituminous materials are studied. The effect of photoluminescence memory of the excitation linear polarization in Georgian crude oils and motor gasolines with different octane numbers is revealed. Photoluminescence and polarization spectra are obtained, and polarization characteristics of media depending on their chemical structure and composition are measured. A Denisyuk reflectance hologram is obtained in a luminescent photoanisotropic gyrotropic material using the linearly polarized coherent light, and its polarization characteristic is studied.

The photoelectron emission has been studied of silver island films excited by a laser pulse of 10-ns duration at three wavelengths: 355, 532, and 1064 nm. It has been shown that, for wavelengths of 355 and 532 nm, the photoemission of island films significantly differs from the photoemission of a bulk sample. For an island film, dependence on the pulse energy characteristic for single-photon emission has been observed at a 355-nm wavelength. It has also been shown that the surface plasmon resonance in nanoparticles significantly affects the photoemission and character of its dependence on the energy of the laser pulse.

With the purpose of creating a thin composite layer of Ag:Si containing Ag nanoparticles (NPs), the effect of a nanosecond pulse produced by ruby laser (λ = 0.694 µm) on single-crystal c-Si implanted with a high dose of Ag⁺ ions is studied. The pulsed laser annealing (PLA) is carried out with an energy density exceeding the melting threshold of amorphous а-Si (W ≥ 1.2 J/cm²). During the PLA, temporal dynamics of reflectivity R(t) of probing laser radiation (λ = 1.064 µm) from the Ag:Si layer is explored and compared to data on the melt existence time obtained by the computer simulation. The morphology of the surface, crystallinity, and spectral optical reflection R(λ) of Ag:Si layers subject to PLA are studied. PLA is found to cause melting and subsequent crystallization of the implanted а-Si with ion-synthesized Ag NPs. In addition, a decrease of the surface roughness from 9 to 3–4 nm and redistribution of Ag NP sizes into two fractions—fine (5–15 nm) and larger (40–60 nm)—are observed. The weakening of plasmon intensity Ag NPs in Si (λ_max = 835 nm) is observed in R(λ) spectra of an Ag:Si layer after PLA as compared with the initial implanted surface. This weakening may be caused by a decrease in concentration of Ag atoms in the immediate proximity to the surface as a result of Ag impurity partial diffusion within the melted layer, as well as Ag partial evaporation during the PLA.

The possibility of efficient difference-frequency generation of terahertz radiation in a metamaterial representing a structure consisting of alternating layers of a semiconductor materials exhibiting intrinsic or metallic conductivity that can be grown by epitaxial methods is investigated theoretically.