Bulletin of the Russian Academy of Sciences: Physics最新文献

The temperature dependences of the magnetization of La_{1 – x}Sr_xFeO_{3 – δ} samples (x = 0.33, 0.50, and 0.67) have been studied. Their Neel temperatures T_N have been determined, at which non-collinear antiferromagnetism (weak ferromagnetism) is settled down in the samples. The introduction of a substituting impurity of strontium into La_{1 – x}Sr_xFeO_{3 – δ} and an increase in its content results in a considerable decrease in T_N. This effect can be compensated using vacuum heat treatment, upon which, on the contrary, a noticeable increase in T_N is observed.

Single-crystal (001) rutile plate was irradiated intensively with 40 keV argon ions. Then, electromigration of oxygen vacancies was done in the irradiated rutile. The effect the concentration and charge state of oxygen vacancies has on the color, optical absorption spectra, and photoluminescence of rutile is shown.

Crystals of the narrow-band semiconductor Pb_{1 – x – y}Gd_xCu_yS (x = 1.1 × 10^–3, y = 2.5 × 10^–3) at temperatures T = 5–300 K demonstrated unusual dependences of the shape of the lines of the electron paramagnetic resonance (EPR) spectra of paramagnetic centers of Gd³⁺ on temperature and microwave power in the resonator of EPR spectrometer. Analysis of the shape parameters of the resonance lines recorded in the X band showed that one of the causes of the unusual changes in the observed EPR spectra of Gd³⁺ centers is a nonuniform distribution of the acceptor impurity of copper with the formation of regions with different concentrations of free charge carriers. Apparently, in these regions, resonance transitions between the spin states of Gd³⁺ centers differently affect the kinetic characteristics of free charge carriers, which lead to different contributions to the quasi-resonant absorption of microwave power.

The problems of synthesis of various allotropic forms of carbon under a laser impact on a carbon-containing target under the conditions of nonequilibrium phase transitions have been considered. The results of studies of the processes of controlled design of certain topological configurations of metal-carbon and diamond-like compounds in a laser experiment with laser ablation and by modeling the 1D–3D structures with a modifyable fractal dimension have been presented. The measurements of the optical and electrophysical characteristics of such structures have been discussed in terms of the possibility of controlling their functional properties.

Impurity paramagnetic complexes [NiF₄F₄F_int]^6–(C_4v), stable associates of the trivalent nickel ion with the interstitial fluorine ion ({text{F}}_{{{text{int}}}}^{-}), were synthesized in BaF₂ ionic crystals with the fluorite structure. The molecular structure of the synthesized complexes was studied by electron paramagnetic resonance at frequencies of 9.39 and 34.25 GHz in the temperature range from 5 to 250 K. It was shown that, in the studied complex, the Ni³⁺ ion (3d⁷, ⁴F, S = 3/2) replaces the lattice cation Ba²⁺ but, under the influence of ({text{F}}_{{{text{int}}}}^{-}) in the neighboring interstice of the octahedral type, is shifted toward it from the center of the coordination cube occupied by it. Under the influence of the crystal field of tetragonal symmetry, the electron spin levels of the complex are split into two Kramers doublets, of which the ground state Kramers doublet turned out to be (left| { pm 1.2} rightrangle ). The energy interval between doublets is approximately 114 GHz. The EPR spectra exhibit a superhyperfine structure caused by the interactions of the electron spin moment of the nickel ion with the nuclei of nine ligand fluorine ions. The parameters of these interactions were determined.

This paper deals with the detection of molecules in a solution using luminescent nanoparticles. Plasmonic nanoparticles change their photoluminescence due to the Purcell and Förster effects, the latter leading to luminescence quenching. Modeling these effects in colloidal solution allows us to determine the conditions of amplification and quenching, which opens the way to improving the sensitivity of sensors based on photoluminescence.

A theoretical model was developed to describe the interaction of a photonic crystal of semiconductor carbon nanotubes and a three-dimensional extremely short laser pulse in the presence of an external magnetic field. Numerical modeling was used to construct the patterns of the time evolution of current density in a medium containing a multilevel impurity. The dependences of the shape of the current density on the external magnetic field and on the hopping integrals between impurity levels were determined.

NaYF₄:Yb³⁺/Er³⁺/Tm³⁺ particles are synthesized in the form of rods with dimensions of 0.21 × 0.77 μm. They exhibit upconversion luminescence in the visible and near-infrared spectral ranges when irradiated at a wavelength of 980 nm. The possibility of using them as multimodal luminescent sensors with temperatures in the range of 250–350 K is shown ratiometrically, based on the emergence of spectral bands at wavelengths of 525, 545, 655, 700, and 805 nm, of particular interest for biological applications.

We presented numerical estimates of the degree of quantum entanglement based on Schmidt mode analysis for ultra-broadband biphotonic states generated in a photonic crystal fiber. We show that these states have a high degree of quantum entanglement even when the source is pumped broadband by femtosecond laser pulses.

The transformation of the Raman spectra from titanium foils after their fluorination in gas mixtures was experimentally studied. It was found that fluorination leads to a strong increase in the intensity of scattering bands from the initial components of the nanocoating of titanium foils. A new strong band at 905 ± 5 cm^–1 and a wide continuum with a maximum at ~1700 cm^–1 also appear and increase in intensity after fluorination.