Luminophores based on doped Li2B4O7 have been studied by a variety of methods (photoluminescence, pulsed cathodoluminescence and kinetics thereof, thermoluminescence, and electron paramagnetic resonance). Different impurities exhibit both interplay and competition. The interplay of impurities is expressed in the luminescence sensitization due to effective excitation energy transfer which occurs in composite impurity centers. Such centers consist of two differently incorporated impurities, one at a cationic site, another imbedded in the anionic structure. The impurities can compete for a particular position in the crystal lattice, and the priority of doping affects the result. The luminescence and thermoluminescence properties observed in the samples are connected with the structure of impurity centers. It is shown that the loss of trapped charge carriers due to instant recombination on the luminescence centers and low-temperature thermoluminescence (below 400 K) diminishes the luminescence yield for the high-temperature (above 400 K) thermoluminescence peak used in dosimetry.

In this paper, we investigated the luminescence and kinetic properties of 1.1-nm-thick colloidal CdSe nanoplatelets rolled up into scrolls in an external electric field in the range of 0–150[Formula: see text]kV/cm. Luminescence spectroscopy revealed that placing CdSe nanoscrolls in an external electric field leads to quenching of the intensity of luminescence bands with an increasing electric field, whereas time-correlated single photon counting measurements demonstrate the acceleration of the relaxation processes of electronic excitation. These effects are due to a reduction in the overlap integral between the electron and hole wavefunctions which is the reason for the emergent field-induced luminescence quenching.

The study delves into the temporal dynamics of luminescence in colloidal Ag 2 S quantum dots, utilizing time series forecasting techniques. Through an analysis of intensity measurements taken at different time intervals, it uncovers temporal trends and utilizes predictive models to anticipate future behaviour of luminescence spectra. The outcomes contribute to a more profound understanding of optimizing experimental conditions and foreseeing the evolution of these nanomaterials over time. Among the tested models, the most robust and effective approaches for predicting the decay of integral intensity within the first hour include polynomial features with regressors, particularly ElasticNetCV, Ridge, and Lasso, with R 2 scores of 0.74, 0.82, and 0.80, respectively. However, upon comparison with the results of additional experiment conducted over a duration of two hours, the Ridge model demonstrated the best performance in predicting the decay of integral intensity.

The study concerns the behavior of optical and colorimetric properties of cadmium telluride semiconductor colloidal quantum dots covered with silica shell (CdTe/SiO2, core/shell) in an external constant electric field has been studied. To date, the electric field is known to lead mainly to quenching and red shift of the luminescence spectra of quantum dots; however, in most of the corresponding studies only the behavior of band-edge luminescence is considered. In this work, in addition to the luminescence due to interband transitions, the effect of the electric field on the trap-related luminescences of core/shell quantum dots is studied. Semiconductor nanocrystals were synthesized by colloidal chemistry methods. The product mixture was a solution of quantum dots in an aqueous medium. To investigate the optical properties of CdTe/SiO2 nanoparticles in an external electric field, a series of samples was fabricated on the basis of an optically passive cellulose film, in the pores of which quantum dots were embedded. The final sample was a cellulose film with quantum dots sandwiched between two glasses with transparent indium tin oxide electrodes. The strength of the constant electric field applied to such structures reached 140 kV/cm. Photoluminescence spectra of the investigated nanostructures were recorded using a CCD spectrometer. As a result of the experiments it was found that the presence and subsequent increase of the external electric field leads to quenching of the intensity of both band-edge and traprelated photoluminescence of quantum dots. This fact is associated with a decrease in the overlap between electron and hole wave functions under the action of the electric field. It is also shown that at moderate field strength there is a slight increase in the total photoluminescence intensity. This observation can be related to impeded charge carrier trapping. The demonstrated quenching of luminescence intensity is also consistent with the results of other authors who have shown a decrease in the absorption of quantum dots in external electric fields. The stability of colorimetric characteristics of the spherical nanoparticles in an external electric field has been demonstrated. The results of the study can be used for development of optoelectronic devices based on CdTe/SiO2 nanoparticles.

We consider the formation of an electric spark from a point anode in atmospheric air when the primary spark channel from a very early stage of its evolution immediately begins to develop in the form of a cluster of highly ionized plasma microchannels. Using laser probing at a wavelength of 1064 nm, spark microchannels are resolved in the near-anode region of the discharge, and the data on the magnitude and distribution of the plasma electron density of single microchannels are obtained. It is shown that during the first nanoseconds after the discharge gap breakdown, the electron density in individual microchannels is distributed nonuniformly and ranges from 1018 to 5 × 1019 cm–3, with characteristic microchannel diameters being of 20–50 μm.

This study addresses the challenge of modeling temperature-dependent photoluminescence (PL) in CdS colloidal quantum dots (QD), where PL properties fluctuate with temperature, complicating traditional modeling approaches. The objective is to develop a predictive model capable of accurately capturing these variations using Long Short-Term Memory (LSTM) networks, which are well suited for managing temporal dependencies in time-series data. The methodology involved training the LSTM model on experimental time-series data of PL intensity and temperature. Through numerical simulation, the model’s performance was assessed. Results demonstrated that the LSTM-based model effectively predicted PL trends under different temperature conditions. This approach could be applied in optoelectronics and quantum dot-based sensors for enhanced forecasting capabilities.

The paper examines the effect of introducing a chlorine atom into the coordination sphere of a rare earth ion for two novel Eu3+ organometallic compounds. Using spectral and time-resolved measurements, we show that the introduction of a chlorine atom provides a way to achieve a significant increase (from 27 to 36

In the study diffraction of a plane wave with a wavelength of 532 nm is modeled, when the wave passes through plasma cylinders with micrometer-sized diameters of 1, 5, and 10 µm. To calculate wave diffraction, three independent methods are employed, which are based on the geometrical optics approximation, the first Rytov approximation, and a representation of the wave field as a series of cylindrical functions. Key limitations to the validity of these methods are discussed together with the accuracy of the computed solutions. The solution of the diffraction problem in the first Rytov approximation is shown to have a wider scope within which this approximation provides reliable results for describing wave diffraction by a plasma formation.

Here, the optical properties of the Nafion polymer membrane containing colloidal CdSe/CdS/ZnS nanocrystals embedded by diffusion have been studied. The CdSe/CdS/ZnS nanocrystals have a core/shell/shell appearance. All experiments were carried out at room temperature (22 ± 2) °C. A toluene solution was used to provide mobility to the active sulfone groups of the Nafion membrane and to embed the nanocrystals inside the membrane. The diffusion process of colloidal CdSe/CdS/ZnS nanocrystals into Nafion proton exchange membrane has resulted in a new molecular complex “Nafion–colloidal CdSe/CdS/ZnS nanocrystals”. The kinetics of the nanocrystals embedding into the membrane matrix was investigated using luminescence analysis and absorption spectroscopy techniques. The embedding rate of CdSe/CdS/ZnS nanocrystals into the Nafion polymer membrane was approximately 4·10−3 min−1. The presence of new luminescence centers in the membrane was proved independently by laser emission spectroscopy. The luminescence spectrum of the resulting molecular complex contains intensity maxima at wavelengths of 538, 588, 643 and 700 nm. The additional luminescence maximum observed at the 643 nm wavelength was not recorded in the original membrane, solvent or in the spectrum of the semiconductor nanoparticles. The luminescence maximum of the colloidal CdSe/CdS/ZnS nanocrystals was registered at a wavelength of 634 nm. The intensity of the luminescence spectrum of the membrane with embedded nanocrystals was found to be higher than the intensity of the secondary emission peak of the initial nanocrystals, which is important for the practical use of the “Nafion–colloidal nanocrystals” complex in optical systems. The lines contained in the luminescence spectrum of the membrane, which has been in solution with colloidal nanocrystals for a long time, registered upon its drying, show the kinetics of the formation of the molecular complex “Nafion membrane–nanocrystals”. Colloidal nanocrystals located in the Nafion matrix represent an analog of a luminescent transducer.

In the study we thoroughly analyze diffraction effects accompanying the laser beam transmission through inhomogeneous plasma microstructures and simulate their diffraction patterns at the object output and in the near field. For this we solve the scalar Helmholtz wave equation in the first Rytov approximation and compute the diffraction spreading of the transmitted beam in free space. Diffraction effects are found to arise within the beam passage through inhomogeneous plasma microstructures even in the simplest approximations of the laser beam interaction with plasma. These effects become strong in the near-field region and significantly distort the patterns of plasma formations, as well as facilitate the appearance of various optical artifacts in the plasma images. By performing numerical simulations, we characterize in detail the features of the visualization of plasma formations in the field of a coherent laser beam registered by a lens system. The calculations are in good agreement with the experimental data. The study can find broad applications in the processing of the laser images of plasma microstructures registered by lens systems in the presence of strong diffraction effects.

In this work, organic light-emitting LEDs based on Eu3+ coordination compounds with β-diketones and acetic and butyric acids were created and studied. At the moment, an active search is underway for new materials to create optoelectronic devices with high luminescent characteristics. One of these characteristics is high color purity and it can be achieved through the use of materials with narrow-band luminescence, for example, compounds based on Eu3+ ions. Complexes based on Eu3+ with 1,1,1-trifluoro4-phenyl-2,4-butanedione and acetic Eu(Cl)(Btfa)(CH3COO) (compound 1), butyric Eu(Btfa)2(CH3(CH2)3COO) (compound 2) acids were synthesized. The LEDs of the synthesized compounds were manufactured using a combined technique including the method of centrifugation and the method of thermal spraying in vacuum. The characteristics of the LEDs were measured by optical spectroscopy. To study the optical properties of the complexes, the powder was placed between two quartz substrates. Photoluminescence spectra were recorded using a SDL-1 spectrometer, an LED with a wavelength of 365 nm and a photoelectronic multiplier operating in linear mode. Electroluminescence spectra were obtained using the Ocean Optics Maya 2000 PRO spectrometer. A linear structure characteristic of Eu3+ ions was observed in the photoluminescence spectrum of the studied complexes. In the electroluminescence spectrum, radiation characteristic of Eu3+ ions is also observed, in addition to it, an additional wide band with a maximum at a wavelength of 390 nm and a half-height width of 61 nm is observed in the short-wavelength region. The operating voltage of the LED was 10 V. A characteristic “cold” white glow was observed for the studied LEDs. In the spectra of photos- and electroluminescence the following main transitions were found for the studied complexes: 5D0 → 7F0 (maxima at wavelengths λ1 = λ2 = 580 nm for compounds 1 and 2), 5D0 → 7F1 (split band, with maxima at wavelengths λ1 = 587 nm, λ2 = 593 nm, λ3 = 600 nm for the compound 1 and λ1 = 592 nm, λ2 = 599 nm for compound 2), 5D0 → 7F2 (split band, with maxima at wavelengths λ1 = 614 nm, λ2 = 619 nm, λ3 = 623 nm for compound 1 and λ1 = 614 nm, λ2 = 618 nm, λ3 = 620 nm for junction 2), 5D0 → 7F3 (split band, with maxima at wavelengths λ1 = 648 nm, λ2 = 652 nm, λ3 = 655 nm for junction 1 and λ1 = 652 nm, λ2 = 655 nm for compound 2). The wide band observed in the electroluminescence spectrum arises due to the contribution of the hole transport layer, due to the through flow of charge carriers through the active radiating layer, which leads to recombination in the PVK OLED layer. An analysis of the volt-ampere characteristics of the manufactured devices showed that they are characterized by two main conduction modes: the first corresponds to a limitation of the current by a spatial charge (0–7 V), the second is a limitation due to the processes of capture of charge carriers (7–23 V). The results of this work can be used in the production of industrial lighting.

The study explore machine learning (ML) techniques to predict temperature-dependent photoluminescence (PL) spectra in colloidal CdSe nanoplatelets (NPLs), leveraging polynomial regression models trained on experimental data from 85 to 270 K spanning temperatures to forecast PL spectra backward to 0 K and forward to 300 K. 6th-degree polynomial models with Tweedie regression were optimal for band energy (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$B_1$$\end{document}) predictions up to 300 K, while 9th-degree models with LassoLars and Linear Regression regressors were suitable for backward predictions to 0 K. For exciton energy (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$B_2$$\end{document}), the Lasso model of degree 5 and the Ridge model of degree 4 performed well up to 300 K, while the Tweedie model of degree 2 and Theil-Sen model of degree 2 showed promise for predictions to 0 K. Furthermore, a GA-based approach was utilized to fit experimental data to theoretical model of Fan and Varshni equations, facilitating a comparative analysis with the ML-predicted curves.

Optical properties of CdTe/SiO 2 core/shell colloidal quantum dots were investigated in external electric field in the range of 0 - 140 kV/cm. Maximum of photoluminescence intensity was centered at 2.39 eV with the full width at half maximum of 0.26 eV. It was found that the photoluminescence intensity of quantum dots tends to decrease by 22% and the integrated luminescence intensity tends to decrease by 23% with increasing electric field to the maximum value. However, an increase in the integrated luminescence intensity in the region of 60 kV/cm was observed. We show that both interband and trap -state luminescence is affected by an external electric field with no Stark shift observed. Based on these results, we propose that relaxation of the excited states in CdTe/SiO 2 core/shell colloidal quantum dots exposed to an external electric field is affected by two fielddependent mechanisms, i.e. field -induced quenching of luminescence and blocking of charge carrier trapping. The obtained results can be useful to gain better understanding of the electric field effect on the optical properties of CdTe/SiO 2 colloidal semiconductor quantum dots and, in particular, on the operation of hybrid organicinorganic LEDs with emitting layers based on the studied nanocrystals.

Different types of ultrafast radiative transitions are considered. The most interesting among them is the case when the radiative transition is accelerated by the configurational transformation of a structural unit where it occurs. Impurity-induced VUV excitation bands of doped Li2B4O7 are attributed to the creation of impurity-bound excitons. When Mn2+ is involved into exciton recombination, the radiative transition in the Mn2+ 3d5 configuration is accelerated and occurs on a sub-nanosecond time scale. Excitation within the UV bands is connected with energy transfer from the structural units formed by the sensitizers (Cu, Sn) and oxygen to Mn2+. In this case, Mn2+ transitions are not accelerated since its excited state appears after complete relaxation of excitation in the corresponding sensitizer’s unit. Pulsed cathodoluminescence decays are rather slow due to very slow transport of electron–hole pairs and excitons in Li2B4O7.

We investigate the temporal correlation between very-high-frequency (VHF, at frequencies of the order of 10–100 MHz), ultrahigh-frequency (UHF, at frequencies within 1–6 GHz), and x-ray (with photon energies more than 10 keV) emissions, which accompany the development of a high-voltage discharge initiated in a long gap at voltages up to 1 MV. The x-ray and UHF emissions are found to emerge starting approximately from the prepulse current onset observed before the discharge gap breakdown and both gradually decay coming to this instant. The UHF emission spectrum is represented with frequencies up to 6 GHz, with the highest spectral power being achieved within 1–2 GHz. The radio emission power drops sharply at frequencies below 1 GHz and increases closer to 150 MHz with the highest spectral power of VHF radiation being reached within 60–90 MHz. The VHF emission can appear before the discharge current and UHF emission onsets in the form of 100-ns-long prepulses, and its intensity significantly increases as the UHF emission starts. The analysis of the temporal correlation between x rays, VHF, and UHF radiations, discharge current, and voltage waveforms indicates that the generation mechanisms of the discharge electromagnetic radiations are difficult to be interpreted in terms of the developing or colliding streamer concepts.

The light field at the output of the Mach–Zehnder interferometer, where one of its arms contains a birefringent sample and a rotating polarizer is placed at the output, has been investigated both theoretically and experimentally. Initially unpolarized light, after passing through the interferometer, becomes partially polarized and carries information about the sample points with equal sums of principal stresses, forming the isopachic field. Depending on the relative path difference at the considered point in the output light field, the degree of polarization varies from 0 to 1. Analyzing this phenomenon allows us to establish the relationship between the intensity of the outgoing light and the azimuth of the rotating polarizer, thereby enabling the determination of the directions of the main optical axes at each point of the birefringent sample, known as the isoclinic field.

Luminescence and colorimetric properties of ultrathin two-dimensional CdSe nanostructures rolled into scrolls 2.5 monolayers thick are studied. It is shown that photoluminescence of samples under study is caused by interband transitions which corresponds to the violet region of the visible spectrum, and transitions involving surface states, which corresponds to the almost entire optical range. The relaxation dynamics of the excited states corresponding to these transitions was studied. The chromaticity coordinates and dominant wavelengths are calculated for ultrathin CdSe nanoscrolls. The colorimetric characteristics of nanoparticles under study are analyzed in comparison with thicker nanoscrolls and quasi-two-dimensional CdSe nanocrystals from the literature sources.

Spectral characteristics of ultrahigh-frequency radiation generated by a pulsed electric spark in a millimeter air gap are studied, together with its temporal correlation with the behavior of the discharge current and voltage in a nanosecond time scale. Systematic features of the UHF emission and general picture of possible phenomena in the spark gap are discussed.

We propose an efficient method for determining the position of the output plane of a phase object, which is registered by a lens system in the presence of a defocusing effect. The method involves the simultaneous employment of 2D diffraction maps of the diffracted wave constructed for its forward and inverse directions of propagation relative to the object output plane. We show that the resultant diffraction pattern obtained for both cases of the wave propagation appears as the two opposite directed diffraction cones with a special narrow zone between them. Within such a zone, there are particular regularities in the behavior of the intensity and phase shift of the wave. The knowledge of these regularities allows one to determine the position of the object output plane with micrometer accuracy, even when a single angle of laser probing is employed.

For the first time, electric spark microchannels are studied using laser probing simultaneously at two wavelengths of 532 nm and 1064 nm. The spark was formed in atmospheric-pressure air in a millimeter-sized gap when applying a high-voltage pulse with an amplitude up to 25 kV with a maximum generator current of ~300 A. It is shown that the transition to laser probing at a wavelength of 1064 nm makes it possible to obtain more informative data on the parameters of plasma microchannels in the stage of their growth, when the microchannels can be in principle resolved as individual objects. For local discharge regions far from electrodes, it is found that microchannels in the growth stage can have a maximum electron density from 8 × 10 18 to 4.5 × 10 19 cm –3 with a characteristic microchannel diameter about 20 µm. Microchannels, while being in the growth stage and not resolved by the interferometry at a wavelength of 532 nm, can have an average electron density of the order of 5 × 10 18 cm –3 .