Journal of Applied Spectroscopy最新文献

Lithium–potassium–borate (LKB) glass was prepared by varying the concentrations of Cr³⁺ dopant using the meltquenching technique. Further, UV-visible absorption, EPR, and FTIR spectroscopy processes were carried out on the prepared samples. Evaluations were also conducted on a wide range of physical parameters. Nonlinear variations in physical parameters were observed for different glasses, indicating Mixed Alkali Effect (MAE). Various optical parameters, including Urbach energy and optical band gap were derived from the optical absorption data. Data from optical absorption were used to evaluate the crystal field and Racah parameters. The calculated bonding parameters suggest a covalent nature. The EPR spectrum of LKB glass doped with Cr³⁺ demonstrates significant signals that are characteristic of Cr³⁺ ions in distorted octahedral symmetry. The FTIR spectrum conveys trigonal BO₃ and tetrahedral BO₄ structural components that exist in the glass material.

Synthesis and characterization of Dy³⁺-activated Ca₃Al₂O₆ phosphor are reported. The phosphor was synthesized by a modified solid-state reaction method with variable concentrations of doping ions (0.5–3.0 mol.%). The synthesized phosphors were characterized by X-ray diffraction (XRD) analysis, and it was revealed that the sample is monophased and crystallizes in a cubic structure. Scanning electron microscopy (SEM) results exhibited an irregular grain size distribution, ranging from 1 to 10 μm. Fourier transform infrared (FTIR) studies confirmed the formation of Ca₃Al₂O₆:Dy³⁺ phosphor. Photoluminescence (PL) excitation and emission spectra were monitored for variable doping concentrations. Ca₃Al₂O₆:Dy³⁺ phosphor emits intense emission bands at 481 and 575 nm (excited at 350 nm) when doped with Dy³⁺ in the host. The corresponding transitions of the doping ion and concentration quenching effect were studied in detail. The 1931 CIE (x, y) chromaticity coordinates (x = 0.26 and y = 0.32) showed the distribution of the spectral region calculated from PL emission spectra. The thermoluminescence (TL) glow curve showed broad peak centres at around 248°C, and it was fitted using the computerized glow curve deconvolution (CGCD) technique. It was found that the deep trapping phenomenon occurs for UV-irradiated samples where the activation energy is high. Trap analysis elucidated the formation of luminescence centres in Dy³⁺-doped phosphors.

Features of transmission spectra of laser radiation of the D₂-line through a nanocell with a potassium-atom vapor column of variable thickness in the range 300–2000 nm are investigated. It is shown that at low laser radiation intensities, a narrowing of the resonance transmission spectrum is observed at thicknesses L = (2n + 1)λ/2 (n is an integer) and a broadening of the spectrum, at thicknesses L = nλ. Velocity-selective optical pumping resonances appear in the transmission spectrum of the nanocell if the laser radiation intensity is increased. They are located at atomic transitions and have a spectral width 13 times smaller than the Doppler width. Resonances in the nanocell are compared with resonances formed by the known saturated absorption technique. The results can be used to form narrow optical resonances in miniature devices containing atomic vapors.

Phosphorescence of In(III)Cl-etioporphyrin-I in thin films of polyvinylbutyral was recorded at room temperature and atmospheric conditions. A series of phosphorescence spectra, based on which the glow duration τ_phos ≈ 42 μs at 298 K was determined, was obtained using a stroboscopic method. A decrease in τ_phos by almost two orders of magnitude with a change in temperature from 77 to 298 K confirmed the quenching effect of atmospheric oxygen in the gas-permeable polymer matrix. The phosphorescence quantum yield at 298 K increased by ~30 times, reaching a value of φ_phos ≈ 0.74% with an increase in the excitation power density by ~300 times.

Vacuum sintering of Cr, Al, graphite, and TiC or Ti powders at 1300°C was used to obtain products of two MAX phases: 312 and 211, the predominant formation of which depends on whether TiC or Ti is taken as the precursor. The 312 MAX phase (Cr_2/3Ti_1/3)₃AlC₂ predominates in the synthesis from Cr:Al:TiC:C, while the 211 MAX phase Cr_1.5Ti_0.5AlC is the predominant product in the synthesis from Cr:Al:Ti:C; α-Al₂O₃, carbides, and chromium oxides are present in these samples as impurities. A combination of x-ray diffraction and x-ray photoelectron spectroscopy methods revealed significant differences in the chemical and phase composition on the surface and in the bulk of these samples. Aluminum and chromium oxides as well as a carbide (Cr₇C₃) are formed on the surface of these MAX phases during the synthesis. Similar behavior is found in the thermal oxidation of Cr₂AlC with the formation of a protective surface layer of α-Al₂O₃/Cr₇C₃. Formation of a protective layer is essential for producing Cr–Ti–Al–Cbased materials with high thermochemical stability in aggressive environments.

The composition and oxidation state of metals in copper amalgam samples obtained by the direct reduction of copper and mercury ions in an aqueous solution were studied by x-ray photoelectron spectroscopy (XPS) in an atmosphere of high-purity argon 6.0. The use of XPS in a high-purity argon medium eliminates the effect of oxygen traces in the residual atmosphere of the spectrometer on the amalgam surface and the investigation results. The order of the reduction of the metal ions in an aqueous formaldehyde solution was shown to affect the content of oxidized copper forms. In the case of simultaneous reduction of copper and mercury ions, the amalgam obtained had an impurity of 5–7 at.% copper as cuprous oxide and 8–10 at.% copper as cupric oxide. After the consecutive reduction of copper ions followed by mercury ions, the resultant amalgam had an impurity of 11–14 at.% copper as cupric oxide. When the copper ions were reduced by washing the resultant powder with dilute acid followed by the reduction of mercury, the resultant amalgam contained an impurity of 9–11 at.% copper as cuprous oxide. The state of mercury in the amalgam was found to be independent of the order of reduction of the metal ions.

Studies were carried out on thin films of ZnO + 15% Co deposited in vacuum (p = 2.2∙10–2 mm Hg) on quartz and silicon substrates by multipulsed high-frequency (f ~ 10–12 kHz) laser action on a ceramic target with laser power density q = 81 MW/cm². The morphology of the resultant films was studied by atomic force microscopy. The transmission spectra of these films are discussed. The photoelectric properties of the ZnO + 15% Co/Si structure are analyzed.

Simulation was used to study the movement of fluoride ions in a superionic lanthanum trifluoride crystal in the dielectric phase upon dynamic elastic deformation caused by propagation of an acoustic wave with frequency not exceeding 100 MHz. The fluoride ion concentration was found to be significantly enhanced in the tensile region and slightly decreased in the compression region. The ionic conductivity can differ by an order of magnitude in the tensile and compressive zones alternating at intervals equal to the half-length of the acoustic wave leading to the formation of localized superionic phase regions.

A formula based on the Fresnel–Kirchhoff diffraction integral formula, which yields the self-reproducing mode of a plano-concave resonator with a nonreflective band on the cavity mirror, was derived and converted into a discrete numerical integral. The Fox–Li iterative method was then used to obtain the self-reproducing mode of the resonator. The results reveal that the nonreflective band transforms the laser mode from the fundamental Hermite–Gaussian (HG) mode to a distributional characteristic that resembles that of high-order HG modes, albeit with minor differences. Therefore, placement of a straight non-reflective band on the cavity mirror of a plano-concave resonator conveniently generates laser field distributions with features of high-order modes.

The photoluminescence (PL) of Ge/Si nanostructures with Ge quantum dots (QDs) was studied at 5, 78, and 300 K. The nanostructures were grown by molecular beam epitaxy on singlecrystal silicon substrates under 2 keV Ge⁺ ion irradiation and without irradiation. Enhanced intensity of the broad PL band in the energy range of ~0.8 eV was found when the nanostructures were irradiated with Ge⁺ ions. A comparative analysis was carried out for the PL spectra recorded from the side of the silicon substrate and from the side of the formation of Ge/Si nanostructures. During the growth of multilayer Ge/Si nanostructures with Ge QDs at 500–600oC, thermal defects of the structure were found to have formed in silicon, causing the appearance of electron-vibrational bands with zero-phonon lines P ~ 0.767 eV, C ~ 0.789 eV, and H ~ 0.926 eV.