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

The electron paramagnetic resonance spectra of Mn²⁺ and Gd³⁺ ions in crystals of the narrow-gap semiconductor Pb_0.996Cu_0.003Mn_xGd_yS (x ( approx ) 6 × 10^–4, y ( approx ) 4 × 10^–4) were discovered to demonstrate an unusually strong dependence of the spin relaxation processes of these ions on temperature and power of X-band microwave radiation acting on the crystal sample in a magnetic field. The observed effect manifests itself as sharp dependences of the line shape parameters of the EPR spectra of Mn²⁺ and Gd³ ions on temperature and microwave power. The results of the experimental study indicate a high efficiency of the exchange interaction between these ions via free charge carriers.

In BaF₂, a crystal of the fluorite structure group, in a helium atmosphere with small additions of fluorine and oxygen, paramagnetic complexes [NiF₄F₄O_int]^6–(C_4v) were synthesized by diffusion from the surface. These complexes are stable associates of a trivalent nickel ion with an interstitial oxygen ion ({text{O}}_{{{text{int}}}}^{ - }). The molecular structure of the synthesized complexes was studied by the electron paramagnetic resonance method at frequencies of 9.65, 34.35, and 94–265 GHz in the temperature range from 4.2 to 120 K. It was shown that the studied complex is formed by Ni³⁺(3d⁷, ⁴F, S = 3/2) and O^–(2p⁵, ²P, S = 1/2) ions. The Ni³⁺ ion replaces the Ba²⁺ lattice cation in the crystal, and the O^– ion is located in the adjacent interstitial site in one of the crystallographic directions (leftlangle {001} rightrangle .) It was determined that, in the synthesized complexes, the ferromagnetic exchange interaction between the Ni³⁺ and O^– ions occurs.

A study of the effect of nanosecond pulsed magnetic fields on the behavior of a photon echo in Y(Lu)LiF₄:Er³⁺ samples determined that the action of a pulsed field leads to nonreciprocity and an asymmetric amplification of the photon echo signal. The effect strongly depends on the orientation of the crystals in the external magnetic field and on the orientation of the pulsed magnetic field relative to the direction of the laser pulses.

The paper studies the spectral and kinetic characteristics of hydroxyapatite samples doped with Eu³⁺ in different molar concentrations (1 and 10%) at an excitation wavelength of 266 nm. For the sample with 1% Eu³⁺, the luminescence decay lifetime was measured at temperatures from 80 to 300 K; the temperature dependence of the luminescence decay lifetime is well approximated by a linear function. The absolute temperature sensitivity for the sample with 1% europium is 0.23 μs/K.

A prototype is proposed and experimentally tested for an optical thermal sensor made of a ground optical fiber with a rough surface, which electrically modulates the phonon–photon interaction and imitates the effect of the Bragg grating. The prototype has an improved detection performance due to the increased surface area and the electromodulation of the active sensor part. The possibilities of applying the scheme in noise-immune temperature monitoring and combining the sensor with light cell technologies in quantum information science are discussed.

The generation of broadband terahertz radiation by optical pulses in a nonlinear uniaxial crystal is studied through numerical simulation. This process is accompanied by the creation of a stable optical-terahertz soliton and an additional broadband terahertz signal.

The dynamics of propagation of electromagnetic pulses consisting of a single field oscillation in a composite system of carbon nanotubes integrated into a polymer matrix was studied. Nanotubes with an impurity energetically isolated from the zone structure of nanotubes were considered. An influence of the composite parameters on the processes of propagation of ultrashort pulses was revealed, which opens up new possibilities for controlling their characteristics in such hybrid systems.

The dynamics of a laser beam in a nonlinear medium with carbon nanotubes under the influence of external electromagnetic fields was theoretically studied. Application of the method of slowly varying amplitudes to the nonlinear wave equation allowed one to derive a modified parabolic equation for the spatiotemporal evolution of a Gaussian beam. The influence of electric and magnetic fields on the main radiation parameters, including the maximum intensity, was estimated. The obtained results demonstrated a significant dependence of the radiation characteristics on both the parameters of the laser beam itself (frequency, initial amplitude) and the external constant electric field.

Ce_0.50Y_0.44–xTb_0.06Eu_xF₃ nanoparticles (x = 0, 0.015, 0.03, 0.06) of single-phase hexagonal structure (CeF₃ matrix) are synthesized via co-precipitation. The average particle size is found to be 14.5 nm. Characteristic emission bands are observed upon excitation at 266 nm: Ce³⁺ (5d → 4f transition), Tb³⁺ (⁵D₄ → ⁷F_J, 480–620 nm), and Eu³⁺ (⁵D₀ → ⁷F_J, 570–700 nm). The temperature dependence of integral intensities and their ratios (Ce³⁺/Tb³⁺, Ce³⁺/Eu³⁺, Tb³⁺/Eu³⁺) are studied in the 80–320 K range of temperatures. The highest sensitivity toward temperature is obtained for ratio Ce³⁺/Eu³⁺ at Eu³⁺ concentration x = 0.03. Kinetic studies of Tb³⁺ luminescence confirm temperature-induced quenching due to enhanced phonon-assisted transfer of energy to Eu³⁺.

A new approach was considered that combines generation methods in optical fibers with a strongly modified dispersion profile and nonlinear crystals with periodic poling. The results of numerical analysis showed the rich potential of such systems for generating quantum states, in particular, for generating ultrabroadband states for two-photon microscopy applications.