341 research outputs found
Luminescence of CsI:Na crystal scintillator under synchrotron radiation excitation
No full textThis work investigates the luminescence properties and energetic structure of emission centers created by NaCs isoelectronic impurities in a well-known CsI:Na scintillation crystal. Using synchrotron radiation excitation at 8 K, high-resolution spectroscopic techniques were employed to probe the electronic transitions and luminescent dynamics within the crystal. The study reveals distinct emission bands that can be attributed to both self-trapped exciton (STE) states and excitons bound to NaCs and defect-related centers, with a clear separation between fast and slow decay components. These findings provide deeper insight into how the NaCs impurity alters the emission behaviour of the CsI host, including modifications to energy transfer and relaxation processes</p
A comparative analysis of structural and luminescent properties of homoepitaxially and quasi-homoepitaxially grown LuAG:Ce single crystalline films under ambient and high pressure
No full textThis work is dedicated to investigating the structural, luminescence and photocurrent characteristics of LuAG:Ce single crystalline films (SCFs) grown using the Liquid Phase Epitaxy method on both LuAG and YAG substrates. The primary objective is to analyze the influence of different growth modes, namely homoepitaxial (HE) and quasi-homoepitaxial (QHE), on the structural and luminescent properties of Ce3+ ions under ambient and high-pressure conditions. Based on the results of XRD measurements, we can conclude that both epitaxial structures are fully relaxed. However, a slight deformation of the garnet lattices is observed, manifesting the inequality of the in-plane and out-of-plane lattice constants of substrates and films. The difference in the energy gap values between positions of 4f-5d1,2 Ce3+ absorption bands (6-12 meV) and the positions of Ce3+ emission band (6 meV) was observed for both LuAG:Ce films and caused by the small differences in local perturbations of garnet hosts for epitaxial structures, grown in HE and QHE modes. The Ce3+ emission intensity in LuAG:Ce HE and QHE films decreases with temperature in the 10-300 K range. The decay time of the Ce3+ luminescence in LuAG:Ce HE film demonstrates a weak temperature dependence in the mentioned range. However, in LuAG:Ce QHE grown film, the decay time of the Ce3+ emission shows notable temperature dependences in the 10-300 K range, probably due to the formation of Ce4+-Pb2+ pair centers. The non-monotonical redshift of the Ce3+ emission band and the increse of the Ce3+ decay time are observed in both LuAG:Ce HE and QHE films under increasing external pressure from ambient to 19 GPa due to the compression and distortion of the crystal lattice. The redshift changes of the Ce3+ emission band on pressure are significantly more complicated for LuAG:Ce QHE-grown film than their HE counterpart. The outcomes of this study contribute to the fundamental understanding of epitaxial growth processes and their impact on the luminescence characteristics of rare-earth-doped materials in single crystalline film form.</p
Two- and Three-Layered Composite Scintillators Based on the Ce3+- Doped GAGG and TbAG Garnets for the Simultaneous Registration of Various Types of Ionizing Radiation
No full textThis work presents our most recent results in the development of composite scintillators using Liquid Phase Epitaxy growth method, based on the single crystalline films and single crystals of garnet compounds for radiation monitoring of different components of mixed ionization radiation fluxes. Such composite scintillators present two and three layered epitaxial structures consisting of two single crystalline films of Ce3+ doped garnets, namely Gd3Al5-xGaxO12:Ce garnet with Ga content x=1.75–2.25 as a first film layer and Tb3Al5O12:Ce garnet as a second film layer. As substrates, the Gd3Al5-xGaxO12:Ce single crystals with fixed Ga concentration x=2.3, 2.5 and 3.0 were used. For estimation of scintillation properties of the respective epitaxial structures (pulse height spectra, light yield and scintillation decay kinetics) we have used three types of ionizing radiation: α–particles (239Pu), β-particles (90Sr + 90Y) and γ–quanta (137Cs).</p
Scintillation properties of multilayered composite scintillators based on the YAG:Ce and TbAG:Ce single crystalline films and GAGG:Ce crystal substrates
No full textThis work demonstrates current progress of our group in developing of two- and three-layered composite for radiation monitoring of various components of mixed ionization radiation fluxes based on the epitaxial structures of Ce3+ doped garnet compounds using the Liquid Phase Epitaxy growth technique. These scintillators contain one or two single crystalline films, dedicated for registration of low-penetrating particles, and bulk single crystal substrates used for detection of high-penetrating γ-rays. For creation of two- and three-layered epitaxial structures, the single crystalline films of Ce3+ doped Y3Al5O12, Tb3Al5O12 and Tb2GdAl5O12 garnets were used. The single crystal of mixed Gd3GaxAl5-xO12:Ce garnet with fixed Ga concentrations of x = 2.3 and 3.0 are utilized as substrates. To assess the scintillation properties of these epitaxial structures, the pulse height spectra, light yield and scintillation decay kinetics were measured under excitation by α–particles (239Pu), β-particles (90Sr + 90Y) and γ–rays (137Cs). Finally, the figure-of merit of composite scintillators under study were calculated for selection of the best epitaxial structures for simultaneous registration α– and β-particles and γ–rays.</p
Acoustic microscopy study on elasto-mechanical properties of Lu3Al5O12:Ce single crystalline films
No full textThis article presents experimental, theoretical, and numerical studies of the propagation of guided ultrasonic waves in a layered epitaxial structure of garnet compounds. A microscopic model, yielding dispersion equations based on material and geometrical properties, was developed. Acoustic microscopy experiments both on YAG:Ce crystal substrate and epitaxial structure containing LuAG:Ce single crystalline films grown using the Liquid Phase Epitaxy growth method onto YAG:Ce crystal substrate revealed distinct phase velocity behaviors. The YAG substrate exhibited consistent velocities, minimally influenced by frequency, while the epitaxial structure showed dispersion, indicating frequency-dependent phase velocities. Experimental results were compared with numerically calculated dispersion curves, showing high agreement in the low-frequency range and minor deviations at higher frequencies. An optimization procedure was developed and applied, starting with the YAG substrate and extending to the LuAG:Ce film/YAG:Ce crystal epitaxial structure. The procedure allowed us to extract material properties, offering valuable insights into the mechanical characteristics of the all-solid-state LuAG:Ce film/YAG:Ce crystal structure. This research represents a significant advancement in understanding ultrasonic wave dynamics in layered structures, particularly unveiling previously unexplored elastic properties of LuAG:Ce single crystalline films as well-known scintillation material.</p
Photoluminescence and Raman spectroscopy of Ce3+ doped Y3Al5O12 single crystalline films grown onto Y3Al5O12 and Lu3Al5O12 substrates
No full textRaman spectroscopy, high spectral resolution luminescence, and X-ray diffraction techniques were employed to study two Ce3+ doped Y3Al5O12 single crystalline films grown by liquid phase epitaxy method onto Y3Al5O12 and Lu3Al5O12 single crystal substrates. Optical spectra were obtained with a micrometer step along the cross-sections of epitaxial structures, allowing excellent differentiation of the film, the transition layer, and the substrate of each sample. X-ray measurements demonstrate the mismatch between the lattice constants of the Y3Al5O12:Ce3+ film and its Lu3Al5O12 substrate, an effect related to different compositions. Consequently, the film grown onto Lu3Al5O12 exhibits higher residual stresses than its counterpart grown onto Y3Al5O12. This was confirmed by a mutual comparison of the Raman bands positions of the films. The luminescence spectra of both samples consist mainly of cerium 5d-4f emission, the intensity of which allows for additional study of epitaxial cross section and estimation of the size of transition layer.</p
"Re-creating" Tadeusz Konwicki’s fiction : "Little apocalypse" and Yurii Andrukhovych’s "Moscoviad"a
No full textOn the basis of a comparative analysis of the worlds presented in Moscoviada by Yurii Andrukhovych and in the Little Apocalypse by Tadeusz Konwicki the article demonstrates the meaning of "metaphorical translation". Using the category proposed by Joseph Brodsky, the author of the article shows how similar characters, who search for their identities, are presented in both books
Growth of nanoparticles in liquid medium using magnetron sputtering technique
No full textTitle: Growth of nanoparticles in liquid medium using magnetron sputtering technique Author: Josef Kučera Department: Department of Surface and Plasma Science Supervisor: Mgr. Yurii Yakovlev, Ph.D., Department of Surface and Plasma Science Abstract: This thesis investigates the preparation of platinum and platinum-ruthenium alloy nanoparticles using magnetron sputtering method on a liquid substrate. Polypropylene glycol with three different molecular weights of 425, 1000, and 4000 was chosen as the liquid substrate. The influence of the different viscosities of these substrates on the size and morphology of the nanoparticles produced in the magnetron was investigated. Dynamic light scattering and transmission electron microscopy methods were used to determine the size of the nanoparticles. Furthermore, the catalytic activity of the produced nanoparticles in an alkaline environment was investigated using the rotating disk electrode technique. Keywords: Nanoparticles, Magnetron Sputtering, Polypropylene glycol, Hydrogen Fuel Cells, Water Electrolyzers, Hydrogen oxidation/reduction reactions
George Yurii Shevelov as a master of academic writing
No full textУкраїнськомовні лінгвістичні праці Юрія Шевельова свідчать про нього як про яскраву авторську індивідуальність. У статті проаналізовано стильові та художні засоби, якими він послуговується, щоб дієвіше впливати на читачів. Зроблено висновок про актуальність його мовної практики для вдосконалення й уточнення сучасних норм українського наукового стилю.Ukrainian linguistic papers by George Yurii Shevelov are evidence of his outstanding author individuality. The article deals with analysis of some stylistic and expressive means, which he uses for more effective influence upon his readers. The conclusion of the study reveals that his language practice is topical for development and improvement of modern standards of Ukrainian academic discourse
George Yurii Shevelov as a master of academic writing
No full textУкраїнськомовні лінгвістичні праці Юрія Шевельова свідчать про нього як про яскраву авторську індивідуальність. У статті проаналізовано стильові та художні засоби, якими він послуговується, щоб дієвіше впливати на читачів. Зроблено висновок про актуальність його мовної практики для вдосконалення й уточнення сучасних норм українського наукового стилю.Ukrainian linguistic papers by George Yurii Shevelov are evidence of his outstanding author individuality. The article deals with analysis of some stylistic and expressive means, which he uses for more effective influence upon his readers. The conclusion of the study reveals that his language practice is topical for development and improvement of modern standards of Ukrainian academic discourse
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