Journal of Applied Spectroscopy最新文献

An improved method for determining the temperature of a laser diode and the thermal resistance of the main elements of an equivalent thermal circuit based on measuring the transient temperature-sensitive characteristics of the forward voltage at the p–n junction in response to a step-like effect of a heating current pulse was proposed. The individual components and the total thermal resistance of the laser diode were experimentally studied and analyzed. It was found that the main contribution to the total thermal resistance, which was ~7.4 K/W, was made by the laser crystal layer itself from the p–n junction to the lower plane (~2.8 K/W) and the AlN-switching thermally conductive substrate (~2.6 K/W), for which no further reduction paths were visible. It was shown that a continuous mode of operation was realized without significant overheating ΔT < 40 K with the threshold I ≈ 2 A exceeded by six times, generation power P ≈ 2.5 W, efficiency ~30%, and differential quantum output η ≈ 60%.

The structure and phase state of Ti–Al–N systems obtained in the form of a coating and a bulk material were comparatively studied. The structure was characterized using x-ray diffraction, energy-dispersive spectroscopy (EDS), and Raman spectroscopy (RS). The use of EDS and RS made it possible to verify the x-ray diffraction data on the phase composition of the samples, which is especially important in the study of multiphase Ti–Al–N coatings, and to identify the features of the coating surface microstructure. The Ti–Al–N coating was obtained by chemical deposition of Ti and Al in an N₂ atmosphere on a Ti substrate with subsequent annealing in vacuum at 700, 800, 900, and 1000°C. The bulk Ti–Al–N sample was obtained by reaction sintering of Ti, Al, and TiN powders in vacuum at 1200 and 1300°C. The Ti₂AlN MAX phase appeared in the coating at a lower temperature than in the bulk sample and was characterized by lower thermal stability. The Ti–Al–N coating was characterized by a greater multiphase nature. The phases Ti₂AlN, Ti₄AlN₃, TiN, Ti₂N, and AlN were detected in it after annealing in vacuum at 900°C. The MAX-phase structure was destroyed at 1000°C. The main phase in the bulk sample after annealing in vacuum at 1300°C was Ti₂AlN with a small admixture of TiN and TiAl. The Ti₂AlN MAX phase was destroyed at 1400°C.

A focus depth optimization method was proposed for signal enhancement and reproducibility improvement in pump-probe collinear double-pulse femtosecond laser-induced breakdown spectroscopy. This method was based on the optimization of the focus depth of the second pulse. The spectral signal intensity showed a stable enhancement with an enhancement factor of ~3, and the signal reproducibility exhibited minimal fluctuations when the focus depth of the second pulse was within the range of 0–2 mm below the sample surface. Additionally, the possible mechanisms behind the observed signal enhancement and improvement in reproducibility were discussed based on the measured plasma temperature and electron density.

Quartz from pegmatite mining wastes in North Karelia (Russia) were studied using atomic emission spectroscopy with inductively coupled plasma, IR spectroscopy, and optical and scanning electron microscopy to reveal the main technological characteristics of quartz that determine the possibility of utilizing it as a promising raw material for high-purity quartz concentrate production. It was shown that mineral inclusions in quartz were mainly represented by feldspars, muscovite, calcite, iron oxides, and borosilicate, which was confirmed by the trace element composition of quartz dominated by Al, Ca, K, and Na. Quartz contains OH-complexes associated with structural impurities of Al, Li and B along with molecular water, which was a part of gas–liquid inclusions. A quartz concentrate with a total impurity content of 160 ppm was obtained by unsorted quartz processing that included electromagnetic separation, microwave exposure, and acid pickling. Production of high-purity quartz concentrate with a total impurity content of <50 ppm in quartz grit with a fineness of 0.5–0.1 mm turned out to be difficult because of micron-sized mineral inclusions, gas–liquid inclusions, and structural impurities that were hard to remove during enrichment.

Nitrogen-doped carbon quantum dots (N-CQDs) were prepared by a one-step hydrothermal method using urea, aniline, and ethylenediamine as raw materials and nitrogen sources which exhibited good fluorescence performance. Spectral characteristics of the samples were analyzed using UV spectrophotometry, fluorescence spectrophotometry, and Fourier transform infrared spectroscopy. Optimal conditions, such as pH, reaction time, and ion concentration were investigated for N-CQDs. Under the optimal conditions (40 μL N-CQDs, buffer solution at pH 6 with a reaction time of 30 min), it was observed that cobalt ions caused a significant fluorescence quenching effect on the prepared N-CQDs, as determined by fluorescence spectrophotometry. The spiked recovery rates ranged from 95.8 to 104.6%, indicating that the N-CQDs could serve as a fluorescent probe for detecting the content of Co(II) in the actual environment. This method could be applied to the monitoring of heavy metal pollution in mine groundwater, the detection results of Co(II) using this method were very similar to ICP-MS, indicating that this method had good application prospects.

The mixing process in Rudner–Levitov chains, which are a one-dimensional lattice of bosonic modes with designed losses in every second mode, has been studied. The mixing time could be significantly reduced by choosing the initial excitation in the system in a special way. An eigenvector of the effective Hamiltonian corresponding to a non-zero eigenvalue of the effective Hamiltonian with the smallest absolute value of the imaginary part must be chosen for the class of single-mode excitations. An initial state localized in two or more modes must be chosen so that it is orthogonal to this eigenvector.

Hydrophilic polyurethane–urea films were obtained using cycloaliphatic diisocyanates and nonionic surfactants such as ethoxylated alcohols and alkylphenols. The effect of the selected modifiers on the phase structure of the resultant materials was assessed using ATR-IR spectroscopy.

The optical absorption spectra of (E)-2-(2-aryl-1-cyanovinyl)-4-cyclopropylthiazole derivatives with different substituents in the para position of the aryl ring have been studied. The measurements were carried out in dimethylformamide solution. The introduction of electron-withdrawing substituents leads to a bathochromic shift since these substituents promote delocalization of the thiazole ring nitrogen and sulfur unshared electron pairs. The absorption bands at 250–450 nm arise from HOMO → LUMO and HOMO–1 → LUMO transitions.

This is the first study of the light emission during the sonolysis of liquid ammonia and of solutions of cerium and silver salts in this solvent at –70°C. A Ce³⁺ luminescence band with a maximum at 400 nm in the moving singlebubble sonoluminescence spectrum generated by ultrasound in a solution of 5·10^–4 M Ce(SO₄)₂ in ammonia was discovered. This band was found in addition to the bubble luminescence continuum usual for liquids (240–800 nm in ammonia). The quenching of this band in the presence of AgNO₃ in ammonia solution indicates that electron acceptor Ag⁺ ions suppress the probable sonochemiluminescence reaction Ce⁴⁺ + ({e}_{s}^{-}) → η(Ce³⁺)^* + (1 − η) Ce³⁺, (Ce³⁺)^* → Ce³⁺ + hν responsible for the detected Ce³⁺ glow. The concentration of Ce4+ in the solution is diminished when it is reduced in this reaction and the sonoluminescence intensity of the Ce³⁺ band also decreases during the sonolysis but then reaches a constant level a few minutes after its onset. This behavior is attributed to the attainment of a dynamic equilibrium between the rates of cerium ion reduction and oxidation: Ce⁴⁺ → Ce³⁺ and Ce³⁺ → Ce⁴⁺, respectively. The one-electron oxidizing agent in the latter reaction is presumably the NH₂ radical, which is another primary product of ammonia sonolysis, in addition to a solvated electron (({e}_{s}^{-})). The formation of Ce³⁺ cations during the sonolysis of a Ce(SO₄)₂ solution was confirmed by the detection of Ce³⁺ photoluminescence. The excitation yield in the sonochemiluminescence reaction η = 2·10^–6.

Spectral methods have been developed for analyzing the equilibrium and kinetics of the complexation process of the known photosensitizer, meta-tetrakis(hydroxyphenyl)chlorine (mTHPC), with monomeric and polymeric derivatives of β-cyclodextrin (β-CD). The study of the binding isotherms showed that mTHPC has a higher affinity for the polymeric derivatives of β-CD studied, namely, carboxymethyl-β-cyclodextrin polymer (CM-β-CDPD) and β-cyclodextrin polymer (β-CDPD), than for monomeric methyl-β-cyclodextrin (M-β-CDMD). Profiles for the change in the relative content of mTHPC inclusion complexes with β-CDs in solution with and without the presence of lipid vesicles were obtained and the dissociation constants of the photosensitizer (PS) molecules were calculated from the content of the inclusion complexes with cyclodextrins. The dissociation of mTHPC from the inclusion complexes with M-β-CDMD takes 1–2 min, while this process takes more than one hour with polymeric CDs, (CM-β-CDPD and β-CDPD). These findings suggest that the complexation of the title chlorine with polymeric and monomeric cyclodextrins may play an essential role in the delivery of photosensitizer to cellular/tissue structures.