Sergii Ubizskii

The optical and vibrational responses of Gd₃Ga₅O₁₂ (GGG) single crystals to 147 MeV Kr-ion irradiations were systematically investigated to clarify defect formation pathways and their influence on luminescence mechanisms. Absorption spectra measured at room temperature reveal a stepwise redshift of the fundamental edge and the progressive development of a broad sub-band-gap tail between 4.4 and 5.3 eV, indicating the accumulation of F- and F⁺-type oxygen-vacancy centers and increasing structural disorder. Raman spectroscopy shows that, despite substantial track overlap at fluences up to 10¹⁴ ions/cm², the crystal preserves its phonon frequencies and linewidths, while peak intensities decrease due to a growing disordered volume fraction. Low-temperature (13 K) photoluminescence demonstrates the persistence of a dominant broad band near 2.4 eV and the emergence of an additional irradiation-induced band at ~2.75 eV whose width increases with fluence, reflecting the formation of vacancy-related defect complexes. Excitation spectra transform from band-edge-dominated behavior in the pristine crystal to defect-tail-mediated excitation in heavily irradiated samples. These results provide a consistent spectroscopic picture of ion-track-induced disorder in GGG and identify the defect states governing its luminescence under extreme irradiation conditions.

This article examines the influence of unintentional Cr3+ and Fe3+ impurity ions on the luminescent properties of Gd3Ga5O12 (GGG) single crystals. The characteristic features of the spectra excited by high-energy syn chrotron radiation in the temperature range of 10–300 K are analyzed. It is shown that at 10 K the lumines cence is dominated by a narrow-band emission of Cr3+ ions arising from the spin-forbidden 2E→4A2 transi tion, which indicates weak electron–phonon coupling and high crystalline homogeneity. It is revealed that with increasing temperature the intensity of this transition decreases significantly, while a broadband lumi nescence emerges, associated with the spin-allowed 4T2→4A2 transition and the contribution of Fe3+ ion emis sion. The temperature evolution of the spectra is shown to result from thermal redistribution of the Cr3+ excit ed-state populations, interlevel state mixing, and partial removal of the spin-forbidden nature of Fe3+ transi tions due to lattice vibrations. Based on the study, conclusions are drawn regarding the role of impurity cen ters in energy transfer and nonradiative relaxation processes. The results are of interest both for fundamental photonics and for the development of efficient luminescent materials and optical devices designed to operate over a wide temperature range.

This study presents a comprehensive Raman spectroscopic and mechanical investigation of Gd₃Ga₅O₁₂ (GGG) single crystals irradiated with 231 MeV ¹³¹Xe ions at fluences ranging from 1 × 10¹¹ to 3.3 × 10¹³ ions/cm². Raman analysis reveals that all fundamental vibrational modes of the garnet structure remain observable up to the highest fluence, with the preservation of garnet crystalline topology/absence of secondary crystalline phases. However, significant line broadening (FWHM increase by 20–100%) and low-frequency shifts indicate progressive lattice disorder and phonon-defect scattering. High-frequency Ga-O stretching modes (A_1g, T_2g ~740 cm⁻¹) remain the most resistant to irradiation, while low-energy translational modes involving Gd³⁺ ions exhibit pronounced degradation and partial disappearance at high fluence. Complementary nanoindentation measurements show radiation-induced softening: hardness decreases by up to ≈60% at 3.3 × 10¹³ ions/cm², consistent with amorphization and overlapping ion tracks (~10–12 μm deep). Raman spectroscopy shows that the garnet lattice remains as the only crystalline phase up to 3.3 × 10¹³ ions/cm², while significant line broadening, mode suppression and a strong hardness decrease indicate progressive structural disorder and partial amorphization of the near-surface region. These results demonstrate that GGG maintains crystalline integrity below the track-overlap threshold (~6 keV/nm) but undergoes strong structural relaxation and mechanical weakening once this limit is exceeded. A new analytical methodology has been developed to quantify radiation-induced structural degradation.

The intrinsic defect-related luminescence of as-grown Gd₃Ga₅O₁₂ (GGG) single crystals was investigated using synchrotron excitation in the vacuum-ultraviolet region. The photoluminescence spectrum at 7 K exhibits a broad emission band centered near ~2.5 eV (≈500 nm), accompanied by narrow 4f–4f transitions of uncontrolled Tb³⁺ impurity ions. Gaussian decomposition of the broad band reveals three components at approximately 3.05, 2.70, and 2.50 eV, attributed to self-trapped excitons (STE), antisite-associated recombination, and F/F⁺-type oxygen-vacancy centers, respectively. Temperature-dependent photoluminescence measurements show that the defect-related luminescence is governed by two thermally activated nonradiative channels with activation energies of ~5–8 meV and 42–56 meV. The shallow channel dominates at 20–50 K, while the main quenching occurs between 100 and 150 K, leading to nearly complete suppression of the broad emission at room temperature. The present results therefore characterize the emission behavior of intrinsic, shallow defect centers in as-grown GGG and contribute to understanding defect recombination pathways that are critical for optimizing garnet-based scintillation and photonic materials.

This study presents a comprehensive Raman spectroscopic and mechanical investigation of Gd₃Ga₅O₁₂ (GGG) single crystals irradiated with 231 MeV Xe ions at fluences ranging from 1×10¹¹ to 3.3×10¹³ ions/cm². Raman analysis reveals that all fundamental vibrational modes of the garnet structure remain observable up to the highest fluence, confirming the structural stability of the lattice without formation of secondary crystalline phases. However, significant line broadening (FWHM increase by 20–100%) and low-frequency shifts indicate progressive lattice disorder and phonon-defect scattering. High-frequency Ga–O stretching modes (A_1g, T_2g ~740 cm^-1) remain the most resistant to irradiation, while low-energy translational modes involving Gd3+ ions exhibit pronounced degradation and partial disappearance at high fluence. Complementary nanoindentation measurements show radiation-induced softening: hardness decreases by up to ≈ 60% at 3.3×10¹³ ions/cm2, consistent with amorphization and overlapping ion tracks (~10–12 μm deep). These results demonstrate that GGG maintains crystalline integrity below the track-overlap threshold (~6 keV/nm) but undergoes strong structural relaxation and mechanical weakening once this limit is exceeded. A new analytical methodology has been developed to quantify radiation-induced structural degradation. The method integrates Raman spectroscopic diagnostics with mechanical nanoindentation data through a unified normalization and logarithmic-slope formalism, enabling precise correlation between vibrational and mechanical responses.

In the current work, nanocrystalline powders with different compositions, namely Li_0.98Pr_0.02NbO₃, Li_0.93Pr_0.02Mg_0.05NbO₃ and Li_0.98Pr_0.02TaO₃ were synthesized for the first time using the method of high-energy ball milling of the starting materials (Li₂CO₃, Nb₂O₅, Ta₂O₅, MgO, Pr₆O₁₁), followed by high-temperature annealing. XRD data analysis confirmed the absence of parasitic phases in the obtained nanocrystalline compounds. The estimated particle sizes ranged from 20 to 80 nm. From the obtained nanopowders, ceramic samples were prepared using specially developed equipment, which allowed for pressing at elevated temperatures with a simultaneous application of a constant electric field. The obtained photoluminescence spectra exhibit characteristic features of Pr³⁺ ions in the crystal structure of LiNbO₃ and LiTaO₃ and are most efficiently excited by UV light. Samples pressed with an electric field application show higher intensity of photoluminescence. Investigations of the temperature dependence of electrical conductivity of the Li_0.98Pr_0.02NbO₃ sample, pressed with the application of an electric field, indicate that the conductivity mechanism is similar to that of LiNbO₃ single crystals and, at high temperatures, is attributed to the lithium conduction mechanism.

The changes in the optical, structural, mechanical properties, and chemical composition of Y₃Fe₅O₁₂/Gd₃Ga₅O₁₂ (YIG/GGG) single crystal structures grown by liquid phase epitaxy, particularly at the interface between the film (Y₃Fe₅O₁₂) and the substrate (Gd₃Ga₅O₁₂), are studied. Different complementary techniques, including optical microscopy, local spectrophotometry, electron probe microanalysis, micro‐Raman spectroscopy, and nanohardness analysis are used. The main finding of the study is an experimental approach, in which the probe of the measuring device (light beam, electron beam, nanoindenter) is directed to the surface of the studied sample in a direction perpendicular to the direction of structure growth, and the surface is scanned along this direction. It allows to obtain the profiles of changes in refractive properties, nanohardness, optical absorption, chemical composition, and intensity of phonon spectrum bands at the transition from the GGG to YIG. It is established that the lengths of the scanning intervals, at which the changes of various properties of a specimen occur, differ significantly. The obtained results are affected by the size of the probes and by the sensitivities of both the particular measuring method and the particular physical property of the material to changes in the chemical composition and crystalline structure of the sample.