Arseny N. Kiryakov

The vibrational properties and crystal structures of rare-earth oxides, specifically yttrium (Y₂O₃) and lanthanum (La₂O₃) ones, were investigated using a combination of density functional theory (DFT) calculations and experimental Raman spectroscopy. Simulated Raman scattering spectra for the reference oxides enabled the identification of vibrational mode symmetries for each phase. By correlating the measured spectra of high-entropy (Y_0.2Eu_0.2Gd_0.2La_0.2Er_0.2)₂O₃ ceramics with DFT results, the crystal structure of the material was determined, and the symmetries of its vibrational modes were assigned. Comparative analysis revealed the presence of the principal La₂O₃ vibrational mode of E_g symmetry at 365 cm^–1 in the high-entropy ceramics. DFT-based modeling provides a useful tool for probing the optical characteristics of rare-earth oxides and can support structural and vibrational characterization. The calculated Raman spectra showed good agreement with both existing theoretical data and experimental results within the acceptable calculation error. This result confirms the applicability of DFT-based modeling for probing the optical characteristics of high-entropy materials, and rare-earth oxide ceramics.

Model experiments were performed on the interaction of swift heavy 220 MeV Xe ions with MgAl₂O₄ spinel crystal with (100), (110), and (111) planes. A computational analysis of the energy parameters of Xe ions in MgAl₂O₄ single crystal was performed, and an estimate of the ion range in the near-surface layer (14 μm) was provided. Optical absorption spectrum was analyzed using polarized light and EPR spectroscopy of initial and irradiated crystals. It has been established that at a fluence of 10¹³ cm⁻² in a sample with an orientation plane (110), 35% more optically active F-type centers are formed. It has been shown that optically active centers V|_Al–O⁻ are observed in an unusual, polarized beam.

A synthetic single crystal of magnesium-aluminate spinel was irradiated perpendicularly to the (111) plane with swift heavy xenon ions with an energy of 220 MeV. The modified layer was attested based on Raman scattering spectra recorded while focusing on the surface. A decrease in surface crystallinity was observed, reflected in the changes in fundamental optical characteristics such as the band gap and the energies of static and dynamic disorder. In this study, we demonstrate, along with the modification of optical characteristics and the formation of a disordered layer, the creation of new optically active centers. The luminescent properties of these centers were analyzed. The effect of temperature flare-up in the 3.4 eV band of the excitation spectrum was determined. The low sensitivity of Cr³⁺ luminescence to SHI is demonstrated.

In In this study, the optical properties of magnesium-aluminate spinel were examined after being irradiated with 220 MeV Xe ions. The research aimed to simulate the impact of nuclear fuel fission fragments on the material. The following measurements were taken during the experiments: transmission spectra in the IR region (190–7000) nm, optical absorption spectra in the range (1.2–6.5) eV, and Raman spectra were measured along the depth of ion penetration from the surface to 30 µm. A peak with a broad shape at approximately 5.3 eV can be observed in the optical absorption spectrum of irradiated spinel crystals. This band is linked to the electronic color centers of F⁺ and F. Meanwhile, the band with a maximum at ~(3–4) eV is attributed to hole color centers. Apart from the typical Raman modes of an unirradiated crystal, additional modes, A1g* (720 cm⁻¹), and Eg* (385 cm⁻¹), manifested mainly as an asymmetric shoulder of the main Eg mode, are also observed. In addition, the Raman spectroscopy method showed that the greatest disordering of crystallinity occurs in the near-surface layer up to 4 μm thick. At the same time, Raman scattering spectroscopy is sensitive to structural changes almost up to the simulated value of the modified layer, which is an excellent express method for certifying the structural properties of crystals modified by swift heavy ions.