Defense of the dissertation of Strelkova Assel for the degree of Doctor of Philosophy (PhD) in the specialty «8D05323 - Technical Physics»

L.N. Gumilyov Eurasian National University, a dissertation defense for the degree of Doctor of Philosophy (PhD) by Strelkova Assel on the topic «Luminescent properties of ceramics based on metal fluorides» to the educational program «8D05323 – Technical Physics».

The dissertation was carried out at the «Technical Physics education department» of L.N. Gumilyov Eurasian National University.

The language of defense is russian

Official reviewers:

Temporary members of the Dissertation Committee:

Scientific advisors:

Zhunusbekov Amangeldy Magmurovich

Lisitsyn Viktor Mikhailovich

The defense will take place on December 26, 2025, at 02:00 PM in the Dissertation Council for the training direction «8D053 – Physical and chemical sciences» in the specialty «8D05323 – Technical Physics» of L.N. Gumilyov Eurasian National University. The defense meeting is planned to be held online.

Link: https://share.kz/gt0y

Address: Астана қаласы, Қажымұқан көшесі, 13, №3 оқу ғимараты № 310 аудиторияда

Abstract (English): The purpose of the dissertation research. The aim of this dissertation is the synthesis and comprehensive investigation of the structure and luminescent properties of ceramic materials based on metal fluorides activated with tungsten, obtained by the method of radiation synthesis, as well as the evaluation of the efficiency of converting excitation energy into luminescence, including under synchrotron excitation. Research objectives. To achieve the goal of the dissertation, the following tasks were set and solved: 1. To synthesis samples of ceramic material based on metal fluorides BaF₂, MgF₂, BaMgF₄, activated with tungsten ions, with variation of the technological parameters of the process. 2. To synthesize ceramic material samples based on metal fluorides BaF₂, MgF₂, BaMgF₄, activated with tungsten ions, under varying technological process parameters. 3. To conduct structural studies of the synthesized materials, determine their phase composition, morphology, and the features of tungsten incorporation into the crystal lattice. 4. To investigate the spectral and kinetic characteristics of luminescence of the synthesized ceramics BaF₂, MgF₂, BaMgF₄, depending on irradiation conditions and modes, as well as preparation of the initial mixture. 5. To study the effect of thermal annealing of ceramic samples on luminescence; to investigate the nature of luminescence of BaMgF₄ ceramics under synchrotron excitation in the vacuum ultraviolet range, determine the mechanisms of energy transfer, and identify the contributions of interband transitions, self-trapped excitons (STE), and defect centers. Research methods. In this study, an experimental setup based on the ELV-6 accelerator at the G.I. Budker Institute of Nuclear Physics, Siberian Branch of the Russian Academy of Sciences (Novosibirsk) was used to synthesize ceramics from refractory inorganic materials. In this study, ceramics based on metal fluorides (BaF₂, MgF₂, BaMgF₄) were produced using radiation synthesis, using a high-energy electron beam with an energy of 1.4 MeV and a power density of 14–20 kW/cm². Irradiation of the samples was carried out at atmospheric pressure and high temperatures, which facilitated the formation of a dense structure without the introduction of additional impurities. The following steps were completed: - Structural and morphological analysis: surface analysis using scanning electron microscopy (SEM), elemental composition determination using energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) analysis to identify the crystal structure using a JSM-IT 200 scanning electron microscope and a Tescan MIRA 3 scanning electron microscope. - Luminescent properties analysis: recording photoluminescence and cathodoluminescence spectra, studying the luminescence kinetics, analyzing the spectra upon excitation with vacuum ultraviolet (VUV) radiation. - Crystal structure analysis of the obtained samples using X-ray diffraction analysis (D8 ADVANCE ECO X-ray diffractometer); - Luminescent properties analysis: recording photoluminescence and cathodoluminescence spectra, studying the luminescence kinetics, analyzing the spectra upon excitation with vacuum ultraviolet (VUV) radiation. - Study of the influence of thermal annealing: assessment of changes in the luminescent properties of samples after heat treatment using a muffle furnace; The main provisions submitted for defense. 1. 1. The radiation synthesis method enables the efficient incorporation of tungsten ions into the BaMgF₄-based ceramic lattice. The introduction of activators (W) into the BaMgF₄ crystal lattice creates highly efficient luminescent centers. 2. Thermal annealing consistently increases the luminescence intensity due to the migration of W ions from the intergranular space to the crystal lattice sites, thereby optimizing the emission centers and energy yield. 3. Under VUV synchrotron excitation (T = 9 K), BaMgF₄ luminescence is determined by the conjugation of interband, self-trapped exciton, and defect-induced transitions. Excitation peaks at 6.45–8 eV and 9.7–10.3 eV determine the channels for efficient energy transfer. Description of the main results. The study resulted in the synthesis of ceramic materials based on metal fluorides (BaF₂, MgF₂, BaMgF₄) using radiation synthesis under high-energy electron beams with an energy of 1.4 MeV and a power density of 14–20 kW/cm². Morphological analysis using scanning electron microscopy (SEM) revealed that the average grain size of the synthesized ceramics is 500–800 nm, and porosity does not exceed 5%, confirming its high density. Elemental analysis using energy-dispersive spectroscopy (EDS) revealed a uniform distribution of components within the crystal structure, and X-ray diffraction (XRD) analysis confirmed the formation of BaF₂, MgF₂, and BaMgF₄ phases without significant foreign inclusions. A study of the luminescence properties excited by vacuum ultraviolet (VUV) radiation with an energy of 10.6 eV revealed intense emission in the 220–450 nm range with peaks at 270 nm, 310 nm, and 390 nm, indicating the presence of effective luminescence centers. Analysis of the emission kinetics revealed two time components: a fast component (τ₁ ≈ 5–10 ns), associated with the recombination of electronic states, and a slow component (τ₂ ≈ 200–250 μs), caused by defect centers. Additionally, thermal annealing at 1000°C for 1 hour revealed a 30–40% increase in luminescence intensity, due to a decrease in the concentration of structural defects and the redistribution of active centers. Quantum-chemical modeling using the density functional theory (DFT) method confirmed that the introduction of activators (e.g., W⁶⁺ ions) leads to a narrowing of the band gap by 0.2–0.3 eV and a change in local states near the conductivity levels. Thus, the experimental and theoretical results demonstrate that radiation synthesis allows the creation of ceramic materials with high luminescence efficiency, making them promising for use in scintillation detectors and optoelectronic devices operating in the vacuum ultraviolet range. Description of the novelty and importance of the results obtained. - The possibility of radiation-assisted synthesis of ceramics for phosphors based on complex alkaline earth metal fluorides BaxMg(2-x)F4 has been established for the first time. The use of radiation synthesis allows the introduction of tungsten ions as an activator without the use of additional substances, which is unachievable with traditional thermal methods. - A new window of parameters for electron-beam synthesis on the ELV-4 setup (E≈1.3 MeV, power density ~45 W/cm², exposure time ~180 min) has been proposed and experimentally validated, compared to the previously described extremely pulsed modes of the ELV-6 setup (E≈1.4 MeV, 20–25 kW/cm², ~1 s), expanding the technological possibilities for the formation of fluoride ceramics. - Comprehensive studies of the spectral, kinetic, and quantitative luminescence characteristics of BaxMg(2-x)F4 ceramics, synthesized for the first time by direct radiation synthesis from a mixture of metallic fluoride powders, have been conducted. Comprehensive studies of the spectral, kinetic, and quantitative luminescence characteristics of BaxMg(2-x)F4 ceramics, synthesized for the first time by radiation synthesis, have confirmed the effectiveness of the new approach. The results obtained are important for the further development of radiation technologies in materials science, as well as for practical use in the creation of new light sources, optical materials, and functional coatings. It is expected that the results obtained in this dissertation will be clearly innovative and can be used as phosphors for LEDs. They also have high potential as scintillation materials. Compliance with directions of development of science or government programs. This dissertation research corresponds to the priority area of "New Materials and Technologies, Safe Products and Designs" and the specialized research area of "Radiation Technologies and Materials for Energy and Optoelectronics." The obtained results on the radiation synthesis of fluoride ceramics and the study of its luminescent properties are consistent with the objectives of the State Program for the Development of Science and Technology, which is focused on the creation of innovative materials with improved performance characteristics and the expansion of the application of radiation technologies in industry. Description of the applicant's contribution to the preparation of each publication. The main results of the dissertation research were published in 8 printed works that correspond to the topic of the dissertation work. Of these, 3 articles in peer-reviewed scientific journals included in the Scopus and Web of Science databases, 2 articles in publications recommended by the Committee for Quality Assurance in Science and Higher Education of the Ministry of Science and Higher Education of the Republic of Kazakhstan, 3 abstracts and reports in International scientific conferences. List of published articles: 1. A. M. Zhunusbekov, A. V. Strelkova, Zh. T. Karipbayev, K. K. Kumarbekov, A. Akilbekov, R. N. Kassymkhanova, M. T. Kassymzhanov, Y. Smortsova, A, I. Popov Luminescence Investigation of BaMgF4 Ceramics Under VUV Synchrotron Excitation //Crystals. – 2025. – Т. 15. – №. 2. – С. 127. (Quartile – Q2, IF-2,4); 2. V. M. Lisitsyn, D. A. Musakhanov, T. G. Korzhneva, A. V. Strelkova, L. A. Lisitsyna, M. G. Golkovsky, A. M. Zhunusbekov, J. T. Karipbaev, A. L. Kozlovsky Synthesis and Characterization of Ceramics BaxMg (2–x)F4 Activated by Tungsten //Glass Physics and Chemistry. – 2023. – Т. 49. – №. 3. – С. 288-292. (Quartile – Q3, IF-0,3); 3. V. M. Lisitsyn, V. A. Vaganov, G. K. Alpyssova, E. V., Kaneva, L. A. Lisitsyna, A. V. Strelkova, I. P., Denisov Radiation synthesis of barium magnesium fluoride activated by tungsten ceramics: structure and luminescence //Eurasian Physical Technical Journal. – 2024. – Т. 21. – №. 4.4. (Quartile – Q4, IF-0,64); Applicant's contribution to the preparation of these articles: All experimental data presented in this dissertation were obtained independently by the author with assistance from staff at the Department of Laser and Light Engineering at Tomsk Polytechnic University and the Industrial Accelerator Development Laboratory at the Institute of Nuclear Physics, Siberian Branch of the Russian Academy of Sciences. A thorough review of the existing literature on the research topic was conducted. The processing and interpretation of the obtained results were carried out in collaboration with the research supervisors. The original draft was also written in compliance with scientific publication requirements.

Dissertation

List of Scientific Works

Consultant's Review

Foreign Consultant's Review

Conclusion of the Research Ethics Committee

Official Reviewer's Review

Official Reviewer's Review