Aizat Bakytkyzy

The photoluminescence (PL) and photoluminescence excitation (PLE) spectra of an EFG-grown (−201) β-Ga₂O₃ single crystal were recorded at 7 and 300 K at the FinEstBeAMS beamline of the MAX IV Laboratory. Excitation–emission maps and fixed-wavelength PLE profiles covered 4.50–10.50 eV at both temperatures. Each temperature series was normalized to its own 5.00 eV intensity and, alternatively, to its own maximum; the reported ratios therefore describe excitation dependence within one series and not an absolute difference in luminescence yield between temperatures. At 7 K, integrated emission at 10.50 eV retains 95.4% of its 5.00 eV value and 89.2% of its maximum. At 300 K, the PLE half-height is 4.55 eV, and the maximum occurs at 4.75–4.80 eV, followed by a decrease to 2.26% of the 5.00 eV value and 2.03% of the maximum at 10.50 eV. Room-temperature ellipsometry on the same factory-polished face places the PLE rise in the rapidly increasing absorption region and yields a penetration depth of approximately 0.24 μm near the PLE half-height and 37 nm at 5.90 eV. A constrained depth-dependent calculation does not reproduce the full decline, so surface capture is retained as one possible pathway rather than an established mechanism. The emission is described by the same effective bands at 3.55, 3.37 and 3.07 eV used in the preceding laser study. Their balance is nearly constant at 7 K, whereas the low-energy spectral weight increases at 300 K under deep-VUV excitation. These spectra provide quantitative reference profiles for energy conversion and carrier capture in β-Ga₂O₃.

Defect-related self-activated luminescence of unintentionally undoped biogenic carbonate-containing hydroxyapatite (HAp) was studied at 12 K under tunable vacuum-ultraviolet excitation at the P66 beamline of PETRA III. X-ray diffraction confirmed the hexagonal P6₃/m apatite framework and an apparent coherent-domain size of approximately 57.7 nm. Raman spectroscopy verified the phosphate framework, B-type carbonate near 1072 cm⁻¹, and a perturbed structural-OH environment, while not identifying defect charge states. Four empirical emission families were resolved at 2.530, 2.995, 3.305, and 3.630 eV. PLE monitored at 504, 426, 375, and 346 nm covers D1–D4 and reveals common excitation regions near 5.3–5.5, 6.1, and 7.06–7.10 eV, together with D2-selective and D4-selective features near 6.50 and 9.83 eV. The D3-centred 375 nm profile is dominated by the 7.10 eV component. Hybrid-functional and G₀W₀ calculations place the ideal-HAp edge near 7.1–7.5 eV; therefore, the common near-7.1 eV PLE feature is treated as the best-supported host-related near-edge/excitonic marker, whereas lower-energy features are assigned cautiously to localized sub-gap absorption. Because PLE is not a direct absorption measurement, the pathway scheme is presented as a conceptual hypothesis rather than a uniquely resolved kinetic model.

This exploratory study compares one pristine NdGaO₃(110) crystal with one crystal irradiated at 1 × 10¹¹ ions cm⁻² and one crystal irradiated at 1 × 10¹² ions cm⁻² using 147 MeV ⁸⁴Kr ions. Because each condition is represented by a single independent specimen, specimen-to-specimen variability is confounded with the irradiation condition, and no specimen-level statistical inference is made. Symmetric X-ray diffraction, condition-averaged confocal micro-Raman spectroscopy, and UV–Vis–NIR transmission were used to compare surface-normal lattice response, local vibrational line shapes, and radiation-induced optical attenuation. The nearly angle-independent XRD shift at 1 × 10¹¹ ions cm⁻² is dominated by a common angular offset, whereas the two surviving harmonics at 1 × 10¹² ions cm⁻² give a model-conditioned estimate ε₁₁₀ = +0.509 ± 0.040%. At the higher fluence, the integrated intensities captured in the coupled θ–2θ condition decrease to 9.35 ± 0.46% for (110) and 1.29 ± 0.06% for (220), while the (220) FWHM ratio reaches 7.83 ± 0.73. These fit-derived errors do not include specimen alignment or between-specimen variability. The archived condition-averaged Raman spectra retain Pbnm-like vibrational groups, while the fitted FWHM values of the 168, 214/215, and 449–470 cm⁻¹ features increase by 15.7%, 19.4%, and 14.8%. The bulk-integrated Nd³⁺ 4f–4f maxima remain stable within the wavelength sampling, whereas the effective R_p-normalized differential attenuation at 275–285 nm reaches 388.7 cm⁻¹. The data support an exploratory description of a strained and diffraction-heterogeneous crystalline layer; complete amorphization, quantitative mosaicity, a damage threshold, track dimensions, and a microscopic defect identity are not established.

NdGaO₃ is an orthorhombic perovskite substrate whose response to swift heavy ions remains insufficiently understood. Here, (001)- and (110)-oriented single-crystal wafers were irradiated with 147 MeV ⁸⁴Kr¹⁵⁺ ions to 1 × 10¹³ ions/cm² and examined by symmetric Cu Kα X-ray diffraction. Peak shifts were evaluated using a two-parameter strain/sample-displacement model; PDXL was used for phase identification and diagnostic whole-pattern fitting, while SRIM and NIST attenuation data were used to compare the ion range with the absorption-weighted X-ray depth. Irradiation strongly reduced and broadened the principal reflections and enhanced diffuse scattering near 2θ ≈ 30°. Corrected normal strains were 0.30% for (001) and 1.20% for (110). Reflection-specific apparent microstrains were 0.29–0.61% and 0.69–1.31%, respectively. A broad component already present in the Pristine (110) profile increased in fitted area by approximately 63% after irradiation. Full orthorhombic-cell and Williamson–Hall outputs from unconstrained powder-profile fitting are mathematically underdetermined for these highly oriented wafers and were not used quantitatively. Attenuation calculations establish strong overlap between the probed depth and the SRIM-defined modified region, although depth gradients in crystallinity prevent unique assignment of residual Bragg intensity. The results demonstrate pronounced anisotropic disorder without additional crystalline phases.

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.

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.

This work investigates a comprehensive temperature-dependent photoluminescence (PL) study (7–300 K) of β-Ga₂O₃ single crystals under 250 nm excitation. The emission consists of three competing bands at ~3.55 eV (J₁), ~3.37 eV (J₂), and ~3.07 eV (J₃), exhibiting a redshift, band broadening, and a crossover near ~140 K with increasing temperature. The novelty of this study lies in the first quantitative investigation of the temperature-dependent photoluminescence of undoped β-Ga₂O₃ single crystals, revealing activation, trap-release, and phonon-coupling parameters that define the competition between STE (Self-trapped exciton)- and DAP-related emission channels. A two-channel Arrhenius analysis of global thermal quenching at E_max (at maximum PL), J₁, and J₂ reveals a common shallow barrier (E₁ = 7–12 meV) alongside deeper, band-specific barriers (E₂ = 27 meV for J₁ and 125 meV for J₂). The J₃ band shows non-monotonic intensity (dip–peak–quench) reproduced by a trap-assisted generation model with a release energy E_rel = 50 meV. Linewidth analysis yields effective phonon energies (E_ph ≈ 40–46 meV), indicating strong electron–phonon coupling and a transition to multi-phonon broadening at higher temperatures. These results establish a coherent picture of thermally driven redistribution from near-edge STE-like states to deeper defect centers and provide quantitative targets (activation and phonon energies) for defect engineering in β-Ga₂O₃-based optoelectronic and scintillation materials.

This work investigates a comprehensive temperature-dependent photoluminescence study (7–300 K) of β- Ga₂O₃ single crystals under 250 nm excitation. The emission consists of three competing bands at ~3.55 eV (J₁), ~3.37 eV (J₂), and ~3.07 eV (J₃). With increasing temperature, the spectra exhibit a redshift, band broadening, and a characteristic crossover near ~140 K. A two-channel Arrhenius analysis of global thermal quenching at λ_max, J₁ and J₂, reveals a common shallow barrier E₁ =7–12 meV alongside deeper, band-specific barriers of E₂=27 meV for J₁ and E₂=125 meV for J₂. The J₃ band shows a non-monotonic intensity (dip–peak–quench), reproduced by a trap-assisted generation term with a carrier-release energy E_rel of order tens of meV, explaining a local maximum around ~170 K. Linewidth analysis using a single-optical-phonon model yields effective phonon energies E_ph≈40–46 meV for the integral spectrum and J₃, consistent with strong electron–phonon coupling; deviations for J₁/J₂ indicate multi-phonon and/or inhomogeneous broadening. These results establish a coherent picture of thermally driven redistribution from near-edge/STE-like states to deeper defect centers, modulated by shallow traps, and provide quantitative targets (activation and phonon energies) for defect engineering in β-Ga₂O₃-based optoelectronic and scintillation applications.