The study is devoted to investigating the efficiency dependence of radiation-assisted ceramic syn... more The study is devoted to investigating the efficiency dependence of radiation-assisted ceramic synthesis based on metal oxides and fluorides on initial powder particle sizes. The synthesis was performed for 30 series of ceramic samples, including MgO, Al2O3, ZnO, ZrO2, MgF2, and complex compositions: cerium-activated yttrium-aluminum garnet (Y3Al5O12), spinel AlMgO4, and tungstate MgWO4. The synthesis efficiency was evaluated on the mixture weight magnitude losses, morphology, and relative weight of the obtained ceramic samples. Based on the analysis of the synthesis results and measuring the particle distribution spectra of the initial materials, the criteria for selecting the initial materials were established, and possible explanations for the correlation between synthesis efficiency and the initial materials morphology were proposed.
YAG:Ce ceramics by the direct action of an electron beam with 1.4 MeV energy were synthesized on ... more YAG:Ce ceramics by the direct action of an electron beam with 1.4 MeV energy were synthesized on a mixture of a stoichiometric composition of Y, Al, and Ce oxides without adding any substances to facilitate the process. The synthesis is realized in a time less than 1 s. The main structural phase of the obtained ceramics is YAG and YAP can be additional. The luminescence characteristics of the synthesized samples, the excitation, luminescence, decay time, and pulsed cathodoluminescence spectra, are similar to those known for YAG:Ce phosphors. The conversion efficiency of the excitation energy into the luminescence of the samples reaches 60–70% of those used for the manufacture of LED phosphors. The set of processes that determine the rate and efficiency of radiation synthesis differs from those occurring during thermal methods by the existence of a high degree of the initial compositions’ ionization under the influence of a radiation flux and a high probability of the decay of electr...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2012
ABSTRACT Explosion initiation energy threshold of silver azide was studied for different laser ra... more ABSTRACT Explosion initiation energy threshold of silver azide was studied for different laser radiation wavelengths. Samples were prepared in the form of pellets (pressed powders), thread-like monocrystals and thin plate polycrystals. A special laser complex was used to perform the experiments. It provided multiparameter measuring of different processes in explosive decomposition of samples. These processes are glowing of decomposing sample, glowing from the irradiated area only, sample acoustic response, shape and energy of a laser pulse. The time resolution for all the experiments made 5 ns and synchronization accuracy made 10 ns.It was found that silver azide demonstrates high sensitivity to laser radiation in its transparent spectral region (1064 nm and 532 nm). The explosion initiation energy threshold made 4–8 mJ/cm2 for both pressed powders with the free surface and for samples with the covered and pressed by a quartz plate surface. Silver azide crystals require approximately 10 times higher energy density to explode. When the samples were acted by UV laser radiation, their sensitivity was from 50 to 500 times lower for the uncovered samples. The covered and pressed samples demonstrated the sensitivity which was close to that for acted by 1064 nm laser radiation.Equal sensitivity of samples to laser radiation with different wavelengths testifies to non-photochemical nature of explosion initiation. The results obtained in the experiments can be consistently explained within the limits of the thermal theory of explosion initiation.
Eastern-European Journal of Enterprise Technologies, 2021
The variety of applications of yttrium-aluminum garnet (YAG)-based luminescent materials and the ... more The variety of applications of yttrium-aluminum garnet (YAG)-based luminescent materials and the morphology necessary for these purposes required the development of many technologies for their synthesis. All synthesis technologies used are complex. The structural phase of yttrium-aluminum garnet is formed with any technology, at temperatures exceeding 1,500 °C. The starting materials for the synthesis are metal oxides of aluminum, yttrium and other oxides for activation and modification. It seems possible to use hard radiation to form a new phase. Radiation synthesis of ceramics is realized in less than 1 s, without the use of any additives and influences. The synthesis was carried out at the electron accelerator of the Institute of Nuclear Physics (Novosibirsk). In this work, we studied the spectral-kinetic and quantitative characteristics of luminescence for the first time obtained by the method of radiation synthesis of ceramic samples of yttrium-aluminum garnet doped with cerium...
Effects of uniaxial stress, temperatures and electron irradiation on nanochain straightening in f... more Effects of uniaxial stress, temperatures and electron irradiation on nanochain straightening in film polymer materials (polytetrafluoroethylene and lavsan) have been studied comprehensively. Essential change in material behavior including chain straightening was found in strain (e) – stress (s) curves.
ABSTRACT The possibility is examined of applying strong electron beams for luminescence control o... more ABSTRACT The possibility is examined of applying strong electron beams for luminescence control of InGaN/GaN lightemitting-diode heterostructures deposited on a sapphire substrate. It is shown that excitation of the samples by an electron beam from the heterostructure side leads to intense luminescence of the GaN and InGaN epitaxial layers, whose characteristics are determined by the prehistory of the samples. Induced emission is detected, arising in separate light-emitting-diode structures when the energy density of the electron beam reaches a threshold value. Transition to the induced emission regime in InGaN quantum wells is accompanied by the appearance of a luminous halo around the excitation zone.
ABSTRACT Synthesis of glass system with the composition (mol. %) 50P2O5-(50 - x)Li2O - xZnO + 5 w... more ABSTRACT Synthesis of glass system with the composition (mol. %) 50P2O5-(50 - x)Li2O - xZnO + 5 wt % Dy2O3 has been described. IR absorption spectra and the kinetics of cathodeluminescence at x ranges from 0 up to 50 has been investigated. With the replacement of Li by Zn, a decrease of the oxygen ions’ packing density and the average phosphate chain length could be observed. The increase of the ZnO quantity in the glass composition results in the luminescence decay time decreased from 240 to 50 μs in the 481 and 573 nm bands: here, the branching coefficient for the 4F9/2 energy level undergoes changes. The luminescence kinetics are well described by the Inokyti-Hiroyama model for the dipole-dipole mechanism.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2014
ABSTRACT MgF2 with a rutile structure is important radiation-resistant material with numerous app... more ABSTRACT MgF2 with a rutile structure is important radiation-resistant material with numerous applications due to its transparency from vacuum ultraviolet to infrared range of photon energies. We present and discuss the results of calculations for basic radiation defects in this crystal. The study is based on the large scale ab initio DFT calculations using hybrid B3PW exchange–correlation functional and atomic basis set. We analyzed the electronic structure, atomic displacements, charge density distribution as well as defect formation energies using large supercells. We compared properties of close and well separated F−H (Frenkel) defect pairs as well as individual defects. We simulated also formation and energetic preference of inert F2 interstitial molecules as sinks of mobile interstitial fluorine atoms which is relevant for material radiation stability. We discussed also diffusion of the primary electronic defects—F centers.
The study is devoted to investigating the efficiency dependence of radiation-assisted ceramic syn... more The study is devoted to investigating the efficiency dependence of radiation-assisted ceramic synthesis based on metal oxides and fluorides on initial powder particle sizes. The synthesis was performed for 30 series of ceramic samples, including MgO, Al2O3, ZnO, ZrO2, MgF2, and complex compositions: cerium-activated yttrium-aluminum garnet (Y3Al5O12), spinel AlMgO4, and tungstate MgWO4. The synthesis efficiency was evaluated on the mixture weight magnitude losses, morphology, and relative weight of the obtained ceramic samples. Based on the analysis of the synthesis results and measuring the particle distribution spectra of the initial materials, the criteria for selecting the initial materials were established, and possible explanations for the correlation between synthesis efficiency and the initial materials morphology were proposed.
YAG:Ce ceramics by the direct action of an electron beam with 1.4 MeV energy were synthesized on ... more YAG:Ce ceramics by the direct action of an electron beam with 1.4 MeV energy were synthesized on a mixture of a stoichiometric composition of Y, Al, and Ce oxides without adding any substances to facilitate the process. The synthesis is realized in a time less than 1 s. The main structural phase of the obtained ceramics is YAG and YAP can be additional. The luminescence characteristics of the synthesized samples, the excitation, luminescence, decay time, and pulsed cathodoluminescence spectra, are similar to those known for YAG:Ce phosphors. The conversion efficiency of the excitation energy into the luminescence of the samples reaches 60–70% of those used for the manufacture of LED phosphors. The set of processes that determine the rate and efficiency of radiation synthesis differs from those occurring during thermal methods by the existence of a high degree of the initial compositions’ ionization under the influence of a radiation flux and a high probability of the decay of electr...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2012
ABSTRACT Explosion initiation energy threshold of silver azide was studied for different laser ra... more ABSTRACT Explosion initiation energy threshold of silver azide was studied for different laser radiation wavelengths. Samples were prepared in the form of pellets (pressed powders), thread-like monocrystals and thin plate polycrystals. A special laser complex was used to perform the experiments. It provided multiparameter measuring of different processes in explosive decomposition of samples. These processes are glowing of decomposing sample, glowing from the irradiated area only, sample acoustic response, shape and energy of a laser pulse. The time resolution for all the experiments made 5 ns and synchronization accuracy made 10 ns.It was found that silver azide demonstrates high sensitivity to laser radiation in its transparent spectral region (1064 nm and 532 nm). The explosion initiation energy threshold made 4–8 mJ/cm2 for both pressed powders with the free surface and for samples with the covered and pressed by a quartz plate surface. Silver azide crystals require approximately 10 times higher energy density to explode. When the samples were acted by UV laser radiation, their sensitivity was from 50 to 500 times lower for the uncovered samples. The covered and pressed samples demonstrated the sensitivity which was close to that for acted by 1064 nm laser radiation.Equal sensitivity of samples to laser radiation with different wavelengths testifies to non-photochemical nature of explosion initiation. The results obtained in the experiments can be consistently explained within the limits of the thermal theory of explosion initiation.
Eastern-European Journal of Enterprise Technologies, 2021
The variety of applications of yttrium-aluminum garnet (YAG)-based luminescent materials and the ... more The variety of applications of yttrium-aluminum garnet (YAG)-based luminescent materials and the morphology necessary for these purposes required the development of many technologies for their synthesis. All synthesis technologies used are complex. The structural phase of yttrium-aluminum garnet is formed with any technology, at temperatures exceeding 1,500 °C. The starting materials for the synthesis are metal oxides of aluminum, yttrium and other oxides for activation and modification. It seems possible to use hard radiation to form a new phase. Radiation synthesis of ceramics is realized in less than 1 s, without the use of any additives and influences. The synthesis was carried out at the electron accelerator of the Institute of Nuclear Physics (Novosibirsk). In this work, we studied the spectral-kinetic and quantitative characteristics of luminescence for the first time obtained by the method of radiation synthesis of ceramic samples of yttrium-aluminum garnet doped with cerium...
Effects of uniaxial stress, temperatures and electron irradiation on nanochain straightening in f... more Effects of uniaxial stress, temperatures and electron irradiation on nanochain straightening in film polymer materials (polytetrafluoroethylene and lavsan) have been studied comprehensively. Essential change in material behavior including chain straightening was found in strain (e) – stress (s) curves.
ABSTRACT The possibility is examined of applying strong electron beams for luminescence control o... more ABSTRACT The possibility is examined of applying strong electron beams for luminescence control of InGaN/GaN lightemitting-diode heterostructures deposited on a sapphire substrate. It is shown that excitation of the samples by an electron beam from the heterostructure side leads to intense luminescence of the GaN and InGaN epitaxial layers, whose characteristics are determined by the prehistory of the samples. Induced emission is detected, arising in separate light-emitting-diode structures when the energy density of the electron beam reaches a threshold value. Transition to the induced emission regime in InGaN quantum wells is accompanied by the appearance of a luminous halo around the excitation zone.
ABSTRACT Synthesis of glass system with the composition (mol. %) 50P2O5-(50 - x)Li2O - xZnO + 5 w... more ABSTRACT Synthesis of glass system with the composition (mol. %) 50P2O5-(50 - x)Li2O - xZnO + 5 wt % Dy2O3 has been described. IR absorption spectra and the kinetics of cathodeluminescence at x ranges from 0 up to 50 has been investigated. With the replacement of Li by Zn, a decrease of the oxygen ions’ packing density and the average phosphate chain length could be observed. The increase of the ZnO quantity in the glass composition results in the luminescence decay time decreased from 240 to 50 μs in the 481 and 573 nm bands: here, the branching coefficient for the 4F9/2 energy level undergoes changes. The luminescence kinetics are well described by the Inokyti-Hiroyama model for the dipole-dipole mechanism.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2014
ABSTRACT MgF2 with a rutile structure is important radiation-resistant material with numerous app... more ABSTRACT MgF2 with a rutile structure is important radiation-resistant material with numerous applications due to its transparency from vacuum ultraviolet to infrared range of photon energies. We present and discuss the results of calculations for basic radiation defects in this crystal. The study is based on the large scale ab initio DFT calculations using hybrid B3PW exchange–correlation functional and atomic basis set. We analyzed the electronic structure, atomic displacements, charge density distribution as well as defect formation energies using large supercells. We compared properties of close and well separated F−H (Frenkel) defect pairs as well as individual defects. We simulated also formation and energetic preference of inert F2 interstitial molecules as sinks of mobile interstitial fluorine atoms which is relevant for material radiation stability. We discussed also diffusion of the primary electronic defects—F centers.
Uploads
Papers by Victor Lisitsyn