In spite of the complicated mechanism of the electroluminescence excitation, the value of the pure electronic transition can be determined from its spectrum if the emitting chromophores ensemble is homogeneous and the starting chromophores in emission are in thermal equilibrium with the environment. The inhomogeneity of the ensemble of electroluminescent chromophores is manifested by the degree of uncertainty of the determined position of the pure electronic transition and can be an indicator of the homogeneity of the material.

A formula is proposed for calculating the spectral position of the peak of non-phonon line (zero phonon line, ZPL) of donor-acceptor (DA) photoluminescence in p- and n-type covalent semiconductors with hydrogen-like impurities at low temperatures and low levels of stationary interband photoexcitation. The model uses a non-stoichiometric simple cubic impurity lattice formed jointly by doping (majority) and compensating (minority) impurity atoms in the crystal matrix. It is assumed that the distribution densities of energy levels of donors forming D⁰-band and energy levels of acceptors forming A⁰-band in the band gap of the crystal are Gaussian with equal root-mean-square fluctuations of the ionization energy. It is considered that the act of non-phonon radiative DA-recombination occurs only between nearest neighbors in the impurity lattice: upon a nonequilibrium electron transition from the energy level of the first excited state of donor to the acceptor energy level in the A⁰-band, which coincides with the Fermi level in this band in a p-type semiconductors or upon a nonequilibrium hole transition from the energy level of the first excited state of acceptor to the donor energy level in the D⁰-band, which coincides with the Fermi level in this band in an n-type semiconductors. The results of calculating the dependence of the maximum of DA-photoluminescence nonphonon line on the concentration and degree of compensation of majority impurities by minority impurities are consistent with the known experimental data for neutron-transmutation doped germanium crystals.

The luminescence of Er³⁺ ions in silica glasses synthesized by the method of direct sol-gel-glass transition and by melting of activated gel grit using various precursors of optical centers has been studied. It was found that one of the ways to essentially increase the half-width of the luminescence band ⁴I_13/2→⁴I_15/2 of these ions is the formation of complex centers including erbium, aluminum, and alkali metal ions.

We have investigated up-conversion luminescence spectra of fluorophosphate glasses doped with rareearth ions Yb³⁺ with concentrations from 4 to 10% and Tm³⁺ with concentrations from 10–5 to 3% CW excited at 975 nm. Observed features of the spectra are the result of several up-conversion processes. Each process corresponds to a different Tm³⁺ excited level and possible nonlinearity (i.e., with a different number of absorbed photons per the emitted one). We used our obtained experimental data to analyze an influence of the pumping power and the doping ions concentration on respective contributions of different processes in the luminescence spectra. We showed that simultaneous appearance of several lines in each observed spectral region is typical for smaller concentrations of Tm³⁺ (much less than a percent) and larger concentrations of Yb³⁺ (4–10 %). Increasing Tm³⁺ concentration up to 3% while having 5% Yb³⁺ concentration leads to localization of the up-conversion spectrum in 755—840 nm band with a maximum near 793 nm.

Based on the use of femtosecond time-resolved pump–probe spectroscopy, it has been found that the presence of plasmonic silver nanoparticles in a hybrid thin-film Ag-CuPc nanocomposites leads to a significant reduction in the relaxation time of induced absorption from an excited singlet state of the copper phthalocyanine film in compared with the pure film. The observed effect is associated with the intersystem crossing acceleration in CuPc molecules located in a nonuniform field near the surface of plasmonic silver nanoparticles in the hybrid nanocomposite. The dependence of the detected effects on the thickness of copper phthalocyanine layers in hybrid (Ag-CuPc)ⁿAg nanocomposites is demonstrated.

Lithium fluoride nanocrystals and crystals were placed on an anode of atmospheric pressure glow discharge and exposed to the discharge components. After exposure the photoluminescence of the studied samples was measured. Based on the luminescence spectra, it was found that in unannealed nanocrystals after exposure to a discharge, color centers with new properties inherent to near-cluster centers are formed, and upon annealing of nanocrystals, the conditions necessary for the formation of near-cluster centers are eliminated. It has been found that when annealed nanocrystals are exposed to a discharge, these necessary conditions are partially restored, that opens up new possibilities for elucidating the processes and mechanisms of the formation of centers with new properties.

Individual electron-nuclear spin systems in solids are promising platforms for the implementation of second-generation quantum technologies. The recognized leader among such systems is the negatively charged nitrogen-vacancy (NV-center) color center in diamond hyperfine coupled to nuclear spins of isotopic carbon-13 (¹³C) which due to their weak interaction with environment are widely used as a quantum memory in emerging quantum technologies. Recently, for this purpose, pairs ¹³C-¹³C of nuclei (dimers) in diamond with NV centers have been proposed and actively studied, since, being transferred to the singlet state, they have extremely long coherence times (minutes at room temperature). Here, the eigenvalues (energies) and eigenstates of the spin Hamiltonian of the NV-¹³C-¹³C system are found and used to calculate the probabilities of EPR transitions between nuclear-spin sublevels of states of the NV center with electron spin projections m_S = 0 and m_S = –1. The expressions obtained form the basis for choosing the optimal parameters of microwave and radiofrequency pulses that transform a particular dimer into the singlet state. We are also presenting the example of such prediction for some specific NV-¹³C-¹³C spin system using the data on spatial positions of the ¹³С spins and on internal spin-spin interactions obtained earlier by quantum chemistry methods.

The reaction of phototransformation of free tryptophan (Trp) and as part of a complex with nanodiamond particles (ND-Trp) in the presence of halocarbon (HC) – chloroform was studied by stationary spectroscopy. It was found that in the presence of chloroform, irradiation of solutions with UV radiation leads to an increase in the fluorescence intensity of the phototransformation products of tryptophan (FTT) – kynurenine and its derivatives. At the same time, a more significant increase in the intensity of integral fluorescence with a maximum of ~460 nm was observed in the ND-Trp system than in the system with free tryptophan. Optimal conditions for this reaction were studied. The applicability of the FTT reaction for the detection of widely used chlorine-containing hydrocarbons has been demonstrated: arochlor 1254 (USA standard) and prochlorase, which is part of the combined fungicide “Zamir”. A new photometric test system has been proposed for the detection of a high degree of sensitivity (up to 10^–6–10^–9 M) in the FTT reaction when irradiated with UV light.

Influence of the structure, sizes and composition of two-layered nanoparticles with a silver nanoshell locating into a copper phthalocyanine films on the summary optical response of hybrid nanomaterial was studied theoretically. Investigation of the surface plasmon resonance absorption (SPRA) band and near-field scattering characteristics of two-layered plasmonic nanospheres was made with the use of the Mie theory taking into account matrix absorption and internal size effects. Is was shown that the SPRA band tuning to the exciton absorption bands of the organic matrix may be made by the fitting of reflection index and volume fraction of a dielectric core into metal nanoshells. In visible spectral range the existence of two attenuation peaks with comparable intensities which are sensitive to the changing of optico-geometrics system parameters was established when the strong coupling regime is realized. The results obtained may be used at the development of nanostructured functional elements of nanophotonics, photovoltaics and sensing.

The spectral-luminescent and photophysical properties of an indotricarbocyanine dye with an orthophenylene bridge in the conjugation chain and two 300 Da polyethylene glycols (PEG) substituents (PD1) and its analogue without PEG (PD2) have been studied. It has been shown that the presence of bulk substituents (PEG300) in the dye structure changes the efficiency of singlet oxygen generation. It has been established that in ethanol for both dyes, when their concentration changes in the range from 5 ∙ 10^–8 to 10^–5 M, the quantum yield of the formation of singlet oxygen γ_Δ has a constant value and amounts to γ_Δ=0.031±0.005 for PD1 and γ_Δ=0.050±0.008 for PD2. In low-polarity chloroform for PD2 a significant increase in γΔ is observed with a change in concentration in the range of 10^–7–10^–5 M from γ_Δ=0.022±0.004 at Cdye=2.6 ∙10^-7 M to γ_Δ=0.104±0.016 at Cdye=5.8 ∙ 10^-5 M, and for PD1 with bulk substituents the quantum yield of singlet oxygen formation has a constant value γ_Δ=0.032±0.003. It has been shown that the increase in the quantum yield of the formation of singlet oxygen with a concentration of PC2 in low-polarity chloroform is due to an increase in the fraction of contact ion pairs in solution and the manifestation of the effect of the anion heavy atom (Br^–). It has been shown that the presence of two chains of PEG300 in the structure of a cationic indotricarbocyanine dye (~770 Da) prevents the counterion from moving away from the dye cation PD1 in lowpolarity chloroform, the dye molecules are in the form of contact ion pairs at any concentration, and due to steric hindrances it is difficult for the chromophore to interact with dissolved oxygen.

The influence of internal heavy atom еffect on the deactivation of triplet states in the presence of molecular oxygen for free bases and metal complexes of porphyrins with Mg(II), Zn(II), Pd(II), and Pt(II) ions in several solvents has been systematically studied. The experiments used laser photolysis techniques and direct measurement of the phosphorescence lifetime for metal complexes with heavy Pd(II) and Pt(II) ions at 293 K and atmospheric oxygen concentration in solution. The results obtained are compared with previously published data on laser photolysis of porphyrin metal complexes, and their partial discrepancy is established. The data obtained are discussed together with the results of the study of analogous compounds in degassed solutions. It has been established that the lifetime of the triplet states of metalloporphyrins at atmospheric oxygen concentration and in deoxygenated solutions is significantly affected by the effect of the internal heavy atom. It has been demonstrated that for triplet states, the polarity of the solvents used, as well as structural features of the compounds under study, have a significant effect.

The dependence of the luminescence spectra of an indole solution in ethanol at 77 K on the excitation wavelength has been studied. A decrease in the ratio of the intensities of phosphorescence and fluorescence has been found upon excitation of indole molecules at the long-wavelength edge of the absorption spectrum. It has been found that this effect is associated with a decrease in the ratio of the quantum yields of the intercombination conversion and fluorescence. It is concluded that the contribution of ¹L_a level to the processes of relaxation of the excited singlet state increases. The lifetime of triplet states does not depend on the wavelength of the exciting radiation.

It is shown with the use of IR-spectroscopy that the mechanism behind tubulene TiO₂ growing as the result of mechanochemical activation of nanosized hydrated titania under conditions of high contact pressure involves formation of Ti-O-Ti bridges followed by transformation of oxide blocks into two-dimension crystalline structures during the course of further mechanochemical activation yielding titania tubules.

This paper summarizes the results of the multi-analytical study of Belarusian icons of 18^th–19^th centuries. The mineral pigments used for their creation had been identified. Some patterns of their use were revealed based on the results obtained.

Epitaxial SiC layers 80 nm thick on Si were grown by molecular beam epitaxy at 950°C. The Raman spectra have a peak at 793 cm^–1, which corresponds to the transverse optical phonon mode of the cubic SiC polytype. It is shown that the increase in photocurrent in the ranges of 1.25—1.4 and 1.5—2.0 eV is associated with defects in the SiC/Si heterostructure. It has been found that the photoluminescence spectra of the SiC/Si heterostructures and the Pt₂Si/SiC/Si structure contain two main emission bands in the blue (2.8 eV) and red (1.9 eV) spectral regions.

The paper presents the results of an experimental study of the phenomenon of stochastic resonance in an optoelectronic artificial spiking neuron (ASN) based on a single photon detector and a vertical-cavity surface-emitting laser. ASN is excited by a periodic signal and noise. It is shown that at the certain value of the noise intensity, a significant amplification of the periodic signal and an increase in the signal-to-noise ratio are observed. The effect of the amplitude and the frequency of a periodic signal on the manifestation of a stochastic resonance in an ASN has been studied.

The article discusses the application of the method of differential optical absorption spectroscopy (DOAS) to the problems of localized methane emission from satellite spectral measurements. It is shown that the application of the DOAS method in a scattering atmosphere can lead to significant errors in the estimates of methane concentrations, and it is proposed to supplement it with a filtering procedure for signals distorted by the effects of atmospheric scattering. The procedure takes into account the correlation of errors in the retrieved concentrations of methane and water due to the uncertainty of the trajectory of photons propagating in the scattering atmosphere. This correlation has been estimated by numerical calculations of the indicated errors for a model atmosphere that includes cirrus clouds and two types of surface aerosols.

By means of numerical simulation, a comparison was made of the features of the formation of spatialenergy profiles (SEP) of visibility zones (VZ) for the first and second methods of observation (MO), taking into account the energy of the noise threshold E_nt. It was confirmed for both MOs that the relation previously used in the literature, when the length of the VZ is uniquely determined by the sum of the durations of the illumination and strobing pulses (photodetector exposure), is valid provided that the maximum value of the signal contrast achieved within the VZ is close to unit. For the second MO, the transformation of the SEP at relatively short working distances into a short, convex asymmetric peak at half height, the maximum of which in the limiting case is shifted to the beginning of the VZ, has been studied in detail. This is explained by the predominant influence of the so-called spatial factor on the formation of SEP. Despite some spatial displacement of the SEP relative to each other for the first and second SN for the case when the duration of the illumination and strobing pulses are not equal, the maximum values of the recorded signals and their contrast, as well as the lengths of the visibility zones for both MOs, with typical parameters, in most cases practically coincide. For a particular case, when the duration of the illumination pulse is less than the duration of the strobe pulse, the SEPs of the VZ for the first and second MO were experimentally obtained, which confirm the results of the performed calculations.

A pure experiment-based work was conducted to investigate the optical characteristics of a thin absorbing single-layer copper film at various annealing temperatures. The study also systematically examined the utilization of spectroscopic ellipsometry as an effective tool for fine-tuning the optical constants of thin films, particularly for achieving specific refractive index (n) and extinction coefficient (k) values. The measurement and analysis involved a thermally deposited thin nano-sized single-layer copper film on a glass substrate, along with a spectroscopic ellipsometer.

The use of thin targets offers optimal conditions for accelerating protons to high energies from lasermatter interaction in the framework of the TNSA (target normal sheath acceleration) mechanism. Twodimensional particle-in-cell (PIC) simulations were performed to investigate the effects of thickness and composition of targets in proton acceleration. We will demonstrate how proton energy increases with the target of a low atomic number Z by examining the energy spectra of the different materials He, C, and Al, whereby the maximum proton energy is obtained with a helium target.

A new, rapid UV spectrophotometry method (UV) for the determination of octadecylamine using ninhydrin as a chromogenic reagent was developed. The solution pH, concentration of ninhydrin, temperature, heating time and coexisted ions have been optimized. Under the optimal conditions, the linear regression equation was A = 0.0108c – 0.0179, and the calibration curve demonstrated linearity over a concentration range of ~1.0–50 mg/L with a correlation coefficient (R²) of 0.9970. The developed method with a high degree of precision and accuracy, good repeatability and cost effectiveness, can be successfully applied for the detection of octadecylamine in the samples of any stage of the potassium flotation process from the salt lake brine.

The nature of the Sm–O bond of samarium-activated alumino-borate-based glasses prepared via the melt-quenching technique was investigated using the Ligand field parameters. Crystal field strength (D_q/B) and Racah parameters B and C were derived from the high-energy region of the absorption spectra. B and C are parameters that describe the influence of the inter-electronic force of repulsion in an atom and hence approximate the strength of the Sm–O bond. The absorption spectra revealed nine bands of transitions from the lower ⁶H_5/2 energy level of Samarium to higher ⁶P_3/2, ⁴I_11/2, ⁶H_j, and ⁶F_k levels (j = 15/2, 1/2, k = 11/2, 9/2, 7/2, 5/2, and 3/2). The Sm-O bond in the prepared glass samples is less covalent due to the high values of D_q, B, and C. While the crystal field (Dq) and Racah parameters (B and C) decreased with an increase in Sm³⁺ contents, the crystal field strength (D_q/B) increased from 7.87 to 7.89. The observed trend affirmed the attenuation of the ionic nature (increase in the covalency) of the Sm–O bond in the glass host. The observed less covalent nature of Sm–O bond was complemented further by the negative values (–0.7444, –0.9018, –0.8821, and –0.8821 for GS0.5, GS1.0, GS1.5, and GS2.0, respectively) of the evaluated bonding parameters of all the glass samples. The prepared glass samples have the required features for laser applications.

C-doped CeO₂ nanoparticles were synthesized by hydrothermal method using glucose as carbon source. The structure of the C-doped CeO₂ nanoparticles was controlled by the concentration of the glucose precursor. The structure and properties of the C-doped CeO₂ nanoparticles were characterized by X-ray diffraction and UV-Vis diffuse reflectance spectroscopy. Microscopic morphology of nanoparticles was characterized by transmission electron microscopy. Photocatalytic activity was assessed by considering the degradation of methylene blue under visible light irradiation. Results show that C-doping significantly improves the photocatalytic activity of CeO₂ nanoparticles because of the combination of extending radiation absorption in visible light and the efficient separation of electron-hole pairs. These findings suggest that the present method is useful for controlling the microstructure and dye degradation properties of C-doped CeO₂ nanoparticles, which is particularly important for catalyst engineering.

Affected by temperature and humidity in the environment, salt crystals expand and accumulate on the surface of murals, causing the pigment layer to peel off, which damages the mural. A method for the rapid and nondestructive detection of salt content in murals using hyperspectral techniques is proposed. The spectral data from mural samples were collected with a spectroradiometer and preprocessed by removing breakpoints with Savitzky‒Golay smoothing. The raw spectra were subjected to continuum removal, logarithm of the reciprocal (LR) processing, multiple scattering correction, and standard normal variate transformation combined with first-order differentiation (FD) and second-order differentiation processing to obtain 15 transformed spectra of different forms. The spectra of samples at different concentration levels were classified, and the characteristic wavelengths were extracted using sample set partitioning based on the joint X–Y distance and successive projection algorithm. The pearson correlation coefficient and variable importance in the projection were used for comparison. Salt concentration estimation models were developed using partial least squares regression (PLSR), support vector regression (SVR), and a random forest (RF) model. The slopes of fit were calculated and compared. The results showed that the reflectance spectra decreased and then increased with increasing salt concentration. The accuracy of RF and SVR was better than that of PLSR, and the R_c², RMSEc, and RPDc values of the RF-LR-FD model were 0.9703, 0.0466, and 16.8350, respectively. Spectral analysis combined with machine learning models has potential for the nondestructive detection of salt in murals.

A scheme for electron acceleration by self-focused q-Gaussian laser pulses in under-dense plasma has been presented. The relativistic increase in the mass of plasma electrons gives nonlinear response of plasma to the incident laser pulse resulting in self-focusing. Under the combined effects of the saturation nature of relativistic nonlinearity of plasma, self-focusing and diffraction broadening of the laser pulse, the beam width of the laser pulse evolves in an oscillatory manner. An electron initially on the pulse axis and at the front of the self-focused pulse, gains energy from it until the peak of the pulse is reached. When the electron reaches the tail of the pulse, the pulse begins to diverge. Thus, the deacceleration of the electron from the trailing part of the pulse is less, compared to the acceleration provided by the ascending part of the pulse. Hence, the electron leaves the pulse with net energy gain. The differential equations for the motion of electrons have been solved numerically by incorporating the effect of self-focusing of the laser pulse.

The aim of this work is to prepare and study titanium dioxide nanoparticles (TiO₂ NPs) that were formed from the leaf extract of green tea using the green synthesis method. Plants were dried for seven days at room temperature and finely ground into a fine powder, after which chemical composition, HPLC analysis, characterization of TiO₂ NPs, and biological evaluation processes were performed. In addition, TiO₂ NPs synthesis was confirmed using UV-visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and high-resolution-transmission electron microscope (HR-TEM). A close analysis indicates that the green tea extract contained polyphenols and flavonoids at varied levels, which may be responsible for its biological activities. HPLC examination indicates the presence of Gallic acid, Protocatechuic, p-hydroxybenzoic, Caffeine acid, Catechin, chlorogenic, rutin, coumaric acid, epicatechin gallate, apigenin-7-glucoside, ferulic acid, chrysin, quercetin, and cinnamic acid, might be responsible for their therapeutic potential. In vitro, antioxidant screening revealed that the scavenging effect of green tea extract has 50% inhibition (IC₅₀) at a concentration level of 19.64±0.13 μg/mL, whereas standard Vit. C showed that at 16.81±0.10 μg/mL. However, in the case of the ABTS model, the scavenging effect of green tea extract has 50% inhibition (IC₅₀) at a concentration level of 33.47±0.21 μg/mL, whereas standard Vit. C showed the same at 29.47±0.17 μg/mL. These results demonstrate that green tea is an excellent antioxidant (i.e., an effective anti-DPPH compound).

We present a super sub-Nyquist Hadamard single-pixel THz imaging system in which the THz waves are modulated by a digital micromirror device and a laser driver. Spatial coding of the THz radiation is performed using the cake-cutting (CC)-order Hadamard basis. THz images are reconstructed from a series of coding sequences of the measurement intensity. We prove that with the use of super sub-Nyquist sampling, single-pixel THz imaging with 87% fidelity and a signal-to-noise ratio of more than 23 dB can be achieved using 10% of the CC-order Hadamard basis patterns. The total variation regularization algorithm is shown to have higher robustness to noise than the Hadamard transform and thus offers a good technical solution for single-pixel THz imaging.

The purpose of this study was to quantitatively analyze coumarin in a binary mixture system and to provide a more accurate and convenient potential for food safety inspection and supervision. This investigation has presented a novel terahertz time-domain spectroscopy (THz-TDS) approach and an optimized least square support vector machine (LS-SVM) to analyze the content of coumarin in the binary mixture of coumarin and vanillin. Terahertz responses of the binary mixtures have been measured and a Savitzky–Golay algorithm has been applied to process the absorption coefficient spectra. The principal component analysis has been used to extract features from the preprocessed data. The excellent prediction results can be obtained using LS-SVM optimized by sparrow search algorithm (SSA) with the coefficient of determination (R²), root-mean-square error, and residual predictive deviation of the prediction set were more than 0.999, 0.001, and 146, respectively. The research shows that the prediction effect of the LS-SVM algorithm optimized by the SSA model is better than that of the support vector machine (SVM) algorithm and LS-SVM algorithm without the SSA model. Our research shows that the combination of THz spectrum and SSAoptimized LS-SVM is very promising for the analysis of coumarin and vanillin binary mixtures, and has great potential for the quantitative analysis of more complex multicomponent mixtures.

This study focuses on the preparation of a high-performance visible light photodetector using nanocrystalline lead sulphide (PbS) thin films. The thin films were deposited onto glass substrates via the chemical bath deposition technique, utilizing an aqueous solution of lead acetate and thiourea. The structural study carried out on the deposited films by X-ray diffraction exhibited a cubic crystal structure with a PbS phase. The optical characteristics of PbS thin films were investigated employing UV-Vis absorption spectroscopy. The absorption spectroscopy was carried out in the wavelength range of 400–1000 nm. The absorbance spectra were utilized to calculate the spectral dependence of several optical parameters: band gap, refractive index, extinction coefficient, dielectric constant, and optical and electrical conductivity. The photocurrent was measured in nanocrystalline PbS thin films under the illumination of specific LED wavelength sources. The quality of the PbS thin film as a photodetector was investigated by determining the rise time, decay time, photosensitivity, specific detectivity, and external quantum efficiency.

Liver cancer and healthy individual serum samples were compared based on their spectral features acquired by Raman and fluorescence spectroscopy to initially establish spectral features that can be considered spectral markers for liver cancer diagnosis. Intensity differences of the characteristic peaks of carotenes, proteins, and lipids in the Raman spectra were clearly observed in liver cancer patient serum samples compared to those of normal human serum samples. The changes in the serum fluorescence profiles of liver cancer patients were also analyzed. To probe the capacity and contrast of Raman spectroscopy as an analytical implement for the early diagnosis of liver cancer, principal component analysis was used to analyze the Raman spectra of liver cancer patients and healthy individuals. Furthermore, partial least squaresdiscriminant analysis was performed to compare the diagnostic performances of Raman spectroscopy for the classification of disease samples and healthy samples. Compared with existing diagnostic techniques, the Raman spectroscopy technique has many advantages such as extremely low sample requirements, ease of use, and ideal screening procedures. Thus, Raman spectroscopy has great potential for development as a powerful tool for distinguishing between healthy and liver cancer serum samples.