Journal of Applied Spectroscopy最新文献

Optically detectable magnetic resonance spectra were measured for ensembles of NV-centers in CVD diamonds with different ¹³C contents. The obtained spectra were described using a model based on the spin Hamiltonian. The magnitude of the magnetic field applied to the sample was estimated using the constructed model and experimental data.

Magnetically induced (MI) transitions of ⁸⁵Rb atoms, D₂-lines 5S_1/2 → 5P_3/2, F_g = 3 → F_e = 1 with circular polarization σ^–, the intensities of which are zero in a zero magnetic field, have been studied experimentally and theoretically. However, their intensities increase significantly in magnetic fields of 0.5–1 kG. The MI transition F_g = 3 → F_e = 1 was used for the first time at the probe radiation frequency to implement the process of electromagnetically induced transparency (EIT). The frequency of the coupling radiation was resonant with the F_g = 2 → F_e = 1 transition. The generated EIT resonance was located on the low-frequency tail of the spectrum. It was shown that EIT resonance was formed only when the probe and coupling radiations had the same circular polarization σ^–. This was true for MI transitions F_e – F_g = ΔF = –2.

Peculiarities of absorption spectra formation of porphine derivatives upon attachment of an NO₂ group to the C_m-position of the tetrapyrrole macrocycle have been studied. The molecular conformation of the substituted porphine molecule was optimized using quantum chemistry methods. The energies of molecular orbitals were determined. Absorption spectra were calculated. It was found that the electronic interaction between the macrocycle and the NO₂ group is determined by the orientation of the nitro group relative to the macrocycle mean plane. It has been established that the energies of the LUMO and HOMO–1 orbitals depend significantly on the dihedral angle θ between the macrocycle mean plane and the nitro group plane, while the energies of the LUMO+1 and HOMO orbitals vary slightly. As a result, the S₀ → S₁ and S₀ → S₂ absorption bands have bathochromic shifts, the magnitudes of which are different and depend on the configurational composition of the transitions. The oscillator strength of the S₀ → S₁ transition turns out to be greatest in the coplanar conformer, which has minimal configuration interaction. The oscillator strength of the S₀ → S₁ transition increases sharply in the orthogonal conformer, in which the LUMO and LUMO+1 are quasi-degenerate. All spectral characteristics can be presented as functions of the weighted sum of cos² θ and cos²2θ, taking into account the configuration composition of the electronic transitions.

A rapid and simple method for identification of oil and fatty products of plant origin by their own fluorescence and diffuse reflection of IR radiation using colorimetry and near-IR spectroscopy is proposed. Analytical signals were recorded using 3D-printed devices with built-in UV and IR LED matrices (390 and 850 nm) and a smartphone with the PhotoMetrix PRO® application installed and FTIR spectroscopy in the near-IR region (10,000–4000 cm^–1) with the NIRA attachment used for the analysis of solids. Diffuse reflectance spectra were processed using the TQ Analyst and The Unscrambler X applications. The studied objects were identified and differentiated using chemometric algorithms, i.e., principal component analysis (PCA) and hierarchical cluster analysis (HCA). The mass fraction of fat in the declared products was determined using univariate and multivariate (PLS algorithm) analyses. Adulterated butter was located separately from natural products on the PCA and HCA graphs. They did not intersect with each other on the dendrogram. Samples of butter with different milk fat mass fractions (61.5, 72.5, 82.5, and 99.0%) were used to construct a calibration relationship and determine the milk fat concentration using the PLS method and univariate analysis. The calibration error (RMSEC) were ≤1.31%; the predictive properties (RMSEP), ≤4.45%. The methods under consideration were tested with samples of butter and vegetable oil products from various manufacturers. The RMSEP values for dairy products was ≤4.97%; for margarine, >10% using multivariate analysis. The relative deviation of the results from the mass fractions of fat indicated on the packaging was ≤4.8% when using univariate analysis. This parameter for margarine was in the range 96.3–96.5%. The results correlated with those of FTIR spectroscopy.

Exploring new material structures of low photocatalytic degradation activity for ultraviolet screening is one of the important methods for improving polyvinylchloride (PVC) performance. As an important kind of ultraviolet (UV) shielding agent material, nano zinc oxide (ZnO) has been applied extensively in many fields due to its outstanding properties. However, the severe aggregation behavior between nanoparticles (NPs) and photocatalytic activity greatly limits the application. In this work, surface modification of ZnO with hydroxyapatite and chitosan (ZnO–Hap/CS) was fabricated. Then via a solution casting technique dispersed within the PVC matrix. The results demonstrated that the obtained composite exhibited the best ultraviolet screening performance greatly decreasing the photocatalytic degradation activity of ZnO. It is expected that this approach is prospective for the large-scale preparation of nano ZnO with excellent UV-blocking performance and low photocatalytic degradation activity.

Fredholm integral equations of the second kind are formulated to describe the anomalous skin effect in metal films on dielectric substrates. An algorithm is developed for numerical solution of the equations based on the quadrature method. As a result of its use for processing published experimental data on the spectral ellipsometry of gold films of different thicknesses on a silicon substrate, the density, relaxation time of the conduction electrons, and dielectric constant of gold are uniquely determined. The dependence of the dielectric constant of gold films on their thickness noted in a number of experimental studies is explained by using a model of the normal Drude skin effect that does not take the excitation of space charge in the film into account when solving the inverse optical problems. The optical fields in gold films are studied for different probabilities of mirror reflection of electrons from the boundary of the films It is found that in sensors for biological solutions with a Kretschmann configuration, structures in which the probability of mirror reflection of electrons from the metallic film–liquid interface approaches unity are to be preferred.

A method is proposed for analysis of the photon-count number distributions (PCD) calculated over the space (pixels) of a stack of fluorescent images obtained in the process of a scanning measurement in fluorescence fluctuation spectroscopy which makes it possible to determine the characteristic brightness and number of molecules of the material being studied. The method is applicable to ergodic systems and is based on a theory of the analysis of Photon Counting Histograms (PCH) developed for single-point measurements. The method is tested on experimentally obtained images of a green fluorescent protein. The obtained results are compared with the results of a single-point experiment and the N&B (Number and Brightness) method, which is most often used for numerical analysis of a stack of fluorescent images obtained in scanning experiments. The estimates of the characteristic brightness and number of molecules of the studied substance are in good agreement with estimates obtained with the aid of the methods of analysis used in this region, which makes it possible to conclude that the theory of the PCH method can be used for analyzing spatial PCDs calculated on the basis of a stack of images. The developed method makes it possible to obtain estimates of the studied parameters based on a selected subregion of a single frame of the image.

A new class of BaLiZn₃(BO₃)₃:RE (RE = Sm³⁺, Tb³⁺, Dy³⁺, and Pb²⁺) phosphors were synthesized with a solid- state reaction method. The minor concentrations of various rare earth (Tb³⁺, Dy³⁺, and Sm³⁺) ions and transition metal (Pb²⁺) ions activated in the BaLiZn₃(BO₃) host matrix were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence spectroscopy. The XRD results of BaLiZn₃(BO₃)3:RE (RE = Sm³⁺, Tb³⁺, Dy³⁺, and Pb²⁺) phosphors confirmed that all the samples have a monoclinic phase. SEM studies revealed that the morphology of BaLiZn₃(BO₃)₃:RE (RE = Sm³⁺, Tb³⁺, Dy³⁺, and Pb²⁺) phosphors was irregular. The photoluminescence emission and excitation spectra show that these phosphors can be effectively excited by near-ultraviolet light-emitting diodes (n-UV), and they all exhibit an efficient orange-red (Sm³⁺, ⁴G_5/2 → ⁶H_7/2), green (Tb³⁺, ⁵D₄ → ⁷F₅), yellow (Dy³⁺, ⁴F_9/2 → ⁶H_13/2), and blue (Pb²⁺, ³P₁ → ¹S₀) emission. All of the above results confirmed that the obtained phosphors could be a potential candidate for n-UV-excited WLEDs.

The background differences in water content of different samples have a very strong influence on the robustness of near-infrared spectroscopy (NIRS). For this reason, this study simulated typical biological water matrix samples with formulated hemoglobin (Hb), glucose (Glc), and distilled water, and attempted to use four different intelligent spectral variable selection algorithms [Competitive Adaptive Reweighted Sampling (CARS), Randomized Frog Hopping Algorithm (RF), Genetic Algorithm (GA), and Variable Projection Importance Algorithm (VIP)] to perform the Hb water interference-resistant feature band preferences, while combining partial least squares (PLS) in parallel to build a robust quantitative model of Hb. In addition, the applicability and validity of the model were validated using three prediction sets P₁, P₂, P₃ with different water backgrounds (the formulation method and composition were kept the same, and only the water content increased sequentially). The results showed that RF, GA, and VIP could effectively screen out the characteristic wavelengths of Hb with low sensitivity to water changes and successfully correct the water effect, but due to the large number of characteristic variables they screened out and the existence of a large number of redundant and water interference variables, this ultimately made the model's robustness less than ideal. The CARS algorithm performed the best, and the RMSEP of the three prediction sets were 0.016, 0.017, and 0.038, which is closer to the RMSECV of the calibration set. Therefore, NIRS combined with the variable selection can reduce the effect of water on model robustness and improve the prediction accuracy of the model by the method of selecting effective wave number intervals, and CARS may be one of the ideal algorithms to solve such problems.

Samples of bacterial cellulose with different contents of carboxyl groups have been obtained. The exchange capacity and degree of swelling of these samples were determined. A procedure was developed for the quantitative spectrophotometric determination of CeO₂ nanoparticles. The immobilization of CeO₂ nanoparticles on oxidized bacterial cellulose was studied. A semi-empirical kinetic model describing the release of nanoparticles from the matrix was formulated.