BULLETIN OF THE L.N. GUMILYOV EURASIAN NATIONAL UNIVERSITY. PHYSICS. ASTRONOMY SERIES

Finite Field-Dependent BRST Transformations as Quantum Canonical Flows in the Batalin-Vilkovisky Formalism

Sudhaker Upadhyay — 2026-09-30

We reformulate finite field-dependent BRST transformations as quantum canonical flows in the Batalin--Vilkovisky field-antifield formalism. The starting point is not an ansatz for the Jacobian but a path between two gauge-fixing fermions. The change of gauge is represented by a one-parameter family of BV Lagrangian submanifolds, while a field-dependent BRST transformation is identified with the field-space projection of a canonical flow generated by the gauge-fixed BV master action. This leads to a gauge-fermion transgression equation in which the Jacobian and the variation of the gauge-fixing fermion are two components of one quantum canonical transport law.

For an anomaly-free theory satisfying the quantum master equation, we show that the partition function is independent of the chosen gauge-fixing path. We then apply the construction to non-Abelian Yang-Mills theory and to the reducible Abelian rank-two antisymmetric tensor theory. In the latter case, the complete ghost and ghost-of-ghost hierarchy is incorporated naturally in the BV master action. Covariant/Lorentz and axial gauges appear as two endpoints of a single BV path. We derive a compact compensation condition for finite field-dependent transformations and identify the precise role of the BV Laplacian in the Jacobian. The resulting framework clarifies the relation between FFBRST transformations, gauge-fixing canonical transformations, and the quantum master equation. It also shows why a local Jacobian cannot be assumed in general: locality is a property of the chosen generator and regularization, not of finite field dependence by itself.

Modified gravity models for inflation with non-minimal coupling trace of energy-momentum tensor of the scalar field and Gauss-Bonnet invariant

Pyotr Tsyba — 2026-09-30

The article studies the inflationary properties of a cosmological model with the scalar field containing a non-minimal coupling with a modified Gauss-Bonnet invariant \beta f(G)f(\varphi) and the trace of the energy-momentum tensor of the scalar field \alpha f(\varphi) T in the framework of a flat, homogeneous and isotropic Friedman-Robertson-Walker Universe. To study the inflationary properties of the model, the chaotic potential, the natural potential, and the Starobinsky potential were selected. Within the framework of the slow-rolling approximation and assuming the coupling constants \alpha and \beta to be small ( \alpha<<1 and \beta<<1), generalized expressions for the scalar spectral index n_s and the scalar tensor ratio r are obtained. In the work, the Cobaya cosmology shell for cosmological calculations together with the Polychord sampler was used to calculate the theoretical values of the scalar spectral index and the scalar-tensor ratio and compare them with the observables. It is shown that for the chaotic potential, only the value of the scalar spectral index agrees with the observed data of Planck2018, and the value of the scalar-tensor ratio r exceeds the observed value. For the natural potential and the Starobinsky potential, both values of the inflationary parameters are consistent with observations. It is shown that for the case f(G)=G and all types of potentials, the coupling parameter \alpha is marginalized in each model, and the coupling parameter \beta does not affect the dynamics of inflationary parameters and is not constrained in any way.

COMPARATIVE CATHODOLUMINESCENCE OF NANOSTRUCTURED AlN AND AlN NANOTUBE/CsI SCINTILLATOR COMPOSITES

Marina Konuhova — 2026-09-30

The cathodoluminescence (CL) response of commercially available aluminium nitride powder, plasma-synthesized AlN nanoparticles, AlN nanotubes, and AlN nanotube/CsI composites was comparatively analysed in the 80–300 K temperature range. The nanostructured material was produced by a highly nonequilibrium direct-current arc-plasma route and contained two characteristic nanotube populations: hollow tubes with diameters of approximately 25–30 nm and thinner, frequently helical tubes with diameters of 2–3 nm; both populations had lengths on the order of 700 nm. At 80 K the commercial AlN powder exhibited a dominant band at 3.47 eV, whereas nanoparticles emitted predominantly near 3.66 eV. The nanotube spectrum was substantially more complex and included components near 2.2, 3.0, and 3.5 eV, indicating a broader distribution of defect and surface-related radiative channels. A single-channel Mott–Seitz treatment of the temperature-dependent 3.47 eV emission yielded an apparent activation energy of about 24 meV. The absence of a measurable peak shift or linewidth broadening, together with the small fitted energy, indicates that the intensity loss cannot be described as conventional thermal quenching alone and is more consistently explained by carrier migration to non-radiative surface states. Addition of 0.25–0.50 wt.% AlN nanotubes to CsI modified the host emission profile, particularly at 80 K, providing spectral evidence consistent with radiative reabsorption and/or interfacial energy redistribution. The results demonstrate that AlN morphology strongly controls the balance between intrinsic, impurity-related, and surface-mediated recombination and underline the potential of AlN/CsI composites for tunable ultraviolet–visible scintillation materials.

High-Entropy Oxide Ceramics: Structure, Synthesis Methods, and Applications

Inesh Zhumatayeva — 2026-09-30

High-entropy materials represent a new class of multicomponent materials formed by mixing five or more elements. Owing to pronounced high-entropy effects, these materials exhibit unique physicochemical properties. In recent years, there has been a steady increase in interest in high-entropy materials, as evidenced by the growing number of scientific publications devoted to high-entropy alloys, ceramics, and oxides.

This review systematizes current knowledge on high-entropy oxide ceramics, presents data aimed at understanding the main types of crystal structures—rock salt, fluorite, perovskite, pyrochlore, spinel, and others—and discusses the principles of synthesis and application of high-entropy oxide ceramics. The role of high configurational entropy in stabilizing single-phase states, as well as the influence of chemical complexity on lattice distortion, diffusion processes, and the formation of the so-called “cocktail effect,” is demonstrated.

The paper outlines the main synthesis methods for high-entropy oxide ceramics, including solid-state, liquid-phase, and gas-phase techniques, and analyzes their effects on phase composition, microstructure, and material properties. The review covers recent studies on the mechanical, thermodynamic, catalytic, and electrochemical characteristics of high-entropy oxides (HEOs), as well as their applications in structural materials and coatings. Promising application areas of high-entropy oxide ceramics are discussed, including thermal barrier coatings, catalytic systems, electrical and ionic conductors, and materials designed for operation under extreme conditions.

The performed analysis reveals correlations between structure, synthesis methods, and properties of high-entropy oxides, providing a foundation for the development of new materials with tailored characteristics.

Study of the Effect of Heavy Krypton Ion Irradiation on the Structural-Phase State and Mechanical Properties of High-Entropy Diborides

Asset Sapar — 2026-09-30

Since nuclear and aerospace technology require the creation of radiation-resistant materials, studying the radiation resistance of high-entropy borides (HEBs) is relevant. They combine the advantages of single-metal diborides, such as high melting point, hardness, and chemical inertness, but exhibit superior radiation resistance. This paper provides a brief overview of the characteristics of HEBs and their synthesis methods. The effect of heavy krypton ion irradiation on the structural and phase state and mechanical properties of (TiHfZrNbTa)B2 HEB synthesized by spark plasma sintering is studied. SRIM calculations showed that at a fluence of ~1015 cm-2, the damage level reaches ~2.3 displacements per atom (dpa) at a depth of up to 12 μm.
Using SEM-EDS, the surface morphology of HEB and the binary diborides NbB2 and TiB2 was analyzed. Irradiation did not significantly alter the surface morphology, but cracks formed in TiB2.
X-ray diffraction analysis showed that the lattice parameters of all borides increased, with the largest change in the lattice parameter a for HEB (0,54%) and in the lattice parameter c for NbB2 (0,61%). This anisotropic lattice deformation likely indicates the accumulation of radiation-induced defects along one of the lattice axes.
Vickers microhardness measurements showed that irradiation causes radiation hardening in HEB and a decrease in microhardness in TiB2.
The obtained results indicate high radiation resistance of high-entropy diboride (TiHfZrNbTa)B2, which makes HEB promising materials for use in high radiation environments.

Investigation of hadron interactions at ultra-high energies based on the study of hadrons characteristics in EAS cores

Алия Аргынова — 2026-09-30

This work is devoted to the study of interactions of primary cosmic radiation particles, which can currently be conducted mainly indirectly, by comparing a limited set of traditional characteristics of extensive atmospheric showers with simulation results. The presented work uses the high-altitude ionisation calorimeter ‘Adron-55’, which has the ability to register the most informative high-energy hadronic component in the stems of the EAS, which provides a deeper level of analysis. To increase the spatial and longitudinal resolution of the Adron-55 installation, it has been upgraded by installing and connecting a lower, ninth row of ionization chambers. This additional measuring layer allows the longitudinal structure of the shower to be refined and the accuracy of the reconstruction of the energy distribution of hadrons at large atmospheric depths to be improved. Based on the accumulated experimental data, a physical programme has been implemented to study the longitudinal, transverse and azimuthal characteristics of WACR showers. Such a comprehensive analysis of the spatial parameters of the cascade provides new information about the mechanisms of development of the hadron component and the interactions of ultra-high-energy UCE particles in the Earth's atmosphere.

Investigation of the Dielectric Properties of PVDF, SKF32, PVA, and PS525 Thermoplastics in the Microwave Frequency Range

Dauren Kadyrzhanov — 2026-09-30

Experimental studies aimed at determining the frequency dependence of the permittivity of thermoplastics in the microwave frequency range are of considerable interest due to their use as matrices for particle-filled polymer composites. The aim of this study was to determine the processing parameters required to produce monolithic specimens of several widely used thermoplastics and to measure the frequency dependence of their complex dielectric permittivity over the frequency range from 100 MHz to 5 GHz. The investigated materials included polyvinylidene fluoride (PVDF), poly(trifluorochloroethylene-vinylidene fluoride) fluoroelastomer (SKF32), polyvinyl alcohol (PVA), and polystyrene (PS525). The specimens were fabricated by hot pressing using an experimental setup with individually optimized holding temperature, applied pressure, and holding time to obtain monolithic products free from visually observable porosity and internal defects. The frequency spectra of the complex dielectric permittivity were measured at room temperature using the Nicholson–Ross–Weir method with a vector network analyzer. The experiments revealed that the hot-pressing conditions differed significantly among the investigated thermoplastics. During the fabrication of polyvinyl alcohol specimens, yellowing was observed, presumably associated with the initial stages of thermal degradation of the material. Within the frequency range of 100 MHz to 5 GHz, the real part of the dielectric permittivity (ε′) ranged from 2.57 to 3.31 for polyvinylidene fluoride, from 2.40 to 3.16 for the fluoroelastomer, and from 3.61 to 4.63 for polyvinyl alcohol. For polystyrene, the value of ε′ remained approximately constant at 2.64 throughout the investigated frequency range. All polymers except polystyrene exhibited pronounced frequency dispersion of the complex dielectric permittivity as well as dielectric losses in the range of 0.05–0.20. In addition, the calculated reflection coefficient from a metal-backed plate ranged from −4 to −2.5 dB for thermoplastics exhibiting significant dielectric losses. The obtained frequency dependences expand the available data on the dielectric characteristics of widely used thermoplastics in the microwave frequency range and may be useful for the development of polymer composite materials with tailored dielectric properties for applications in electronics, microwave engineering, and electromagnetic wave-absorbing materials.

Radiation Detection with Wide- and Ultrawide-Bandgap Semiconductors: Detector Fundamentals and Performance Benchmarks for 4H-SiC, GaN, and β-Ga₂O₃

Kanatbek Nalibay — 2026-09-30

Wide - and ultrawide-bandgap semiconductor materials have been receiving growing attention for the application in radiation detectors for nuclear energy systems and other environments with high levels of radiation. The wide- and ultrawide-bandgap semiconductor materials have the advantages of high breakdown strength, low leakage current, and the ability to operate at elevated temperatures. In this review, the state of the art in the field of radiation detectors based on 4H-SiC, GaN, and β-Ga₂O₃ is discussed, with particular focus on the effect of the intrinsic properties of the semiconductor materials on the performance of the detectors. The parameters of particular importance for the detectors are charge collection efficiency, energy resolution, leakage current, thermal stability, and signal drift.

Among these materials, the case for 4H-SiC is the most developed, with a significant experimental base for charged particle and neutron detection, including converter-assisted detectors, as well as operation at elevated temperatures. GaN has also been found to have significant potential, especially for Schottky and vertical detectors for charged particle detection. However, its performance is often heavily dependent on the quality of the interface. β-Ga₂O₃, as a relatively new ultrawide bandgap semiconductor, is seen to have significant potential for X-ray detectors and extreme environment operation. Although, many issues regarding its response to irradiation damage and its recovery after exposure are currently under investigation.

This review aims to compare these three material systems from a common perspective, thereby revealing their current capabilities as well as their most possible areas of application. A comparative summary section and an outlook section have been added to identify the main areas for future work, particularly in terms of standardized benchmarking, defect-informed device optimization, as well as more reliable detectors for nuclear and harsh-environment applications.

Effect of the Synthesis Method on the Formation, Surface State, and Optical Properties of Colloidal CdSe Nanoplatelets

Yerkebulan Koshkinbayev — 2026-09-30

The development of approaches for controlling the thickness, structural uniformity, and surface chemical state of CdSe nanoplatelets is important for obtaining materials with tailored and reproducible spectroscopic characteristics. This work presents a comparative study of CdSe nanoplatelets synthesized by gradual heating using pre-synthesized cadmium myristate and by hot injection of an organoselenium precursor into a reaction medium containing cadmium acetate and oleic acid. The selected synthesis method was shown to have a pronounced effect on the formation process, thickness, and uniformity of the nanoplatelets. Under gradual heating, nanoplatelet formation is preceded by the appearance of intermediate CdSe-containing nanoparticles, while the final product consists predominantly of 4 ML nanoplatelets with a minor fraction of 3 ML species. The hot-injection method yields a more uniform population of 3 ML nanoplatelets. In both samples, the formation of a cubic sphalerite-type CdSe structure was confirmed, whereas the sample obtained by gradual heating exhibited more pronounced structural heterogeneity. Differences in nanoplatelet thickness and uniformity are reflected in their optical properties and surface state. Analysis of the carboxylate groups and elemental composition indicates differences in the local environment of the surface ligands and suggests the probable presence of a residual cadmium–myristate component in the sample synthesized using cadmium myristate. The results demonstrate that the nature of the cadmium precursor, the mode of formation of its carboxylate species, and the selenium introduction conditions jointly determine the structural, surface, and spectroscopic characteristics of CdSe nanoplatelets.

Development of technology for producing high-density ceramics based on Zr0.85(Y, Ce, Ca, Mg)0.15O2 nanoparticles with a high proportion of nanosized grains

Юрий Гаранин — 2026-09-30

In this study, we developed a technology for producing high-density ceramics based on Zr_0.85(Y, Ce, Ca, Mg)_0.15O₂ nanoparticles by implementing a grain boundary diffusion densification mechanism. It was found that standard sintering at 1500 °C leads to an excessive increase in the average grain size to 1–5 μm and microstructural heterogeneity. At the same time, implementing the grain boundary diffusion densification mechanism using low-temperature sintering at temperatures of 1100–1200 °C leads to the formation of high-density (~98–92% of the theoretical density) ceramics with a high proportion of nanosized grains (up to 64%).

- Влияние соотношения газов C₂H₂/O₂ на структуру, механические свойства и адгезионную прочность биокомпозиционных покрытий HAp/Ti, полученных методом детонационного напыления

Ainur SERIKBAIKYZY — 2026-09-30

This paper presents the results of a study of biocomposite coatings based on hydroxyapatite (HAp) and titanium, produced by detonation spraying using a CCDS-2000 system. The aim of the study was to determine the effect of the C₂H₂/O₂ gas ratio during detonation spraying on the structure, phase composition, mechanical properties, and adhesive strength of the HAp/Ti biocomposite coatings. The substrate was a titanium alloy, Ti13Nb13Zr, pre-treated with air abrasives to enhance coating adhesion.
Comprehensive coating studies were conducted using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray diffraction (EDS), nanoindentation, and scratch testing. It was found that varying detonation spraying conditions significantly affects the coating thickness, phase distribution uniformity, and mechanical properties. The densest and most uniform structure was formed under optimized spraying conditions, which ensured increased nanohardness, cohesive strength, and adhesion resistance of the coatings.
Elemental mapping confirmed the formation of a gradient structure in the Ti/HAp coatings, with a gradual transition from metallic layers to calcium phosphate phases. X-ray diffraction analysis revealed the presence of predominantly CaO and TiO₂ phases, with hydroxyapatite components remaining after spraying. Maximum adhesive strength and coating stability were obtained for samples formed under the optimal C₂H₂/O₂ gas ratio.
Regularities in the influence of the C₂H₂/O₂ gas ratio on the structure formation and performance properties of the coatings were established, enabling optimization of detonation spraying conditions to produce coatings with improved performance.
The obtained results indicate the high potential of detonation spraying for the creation of biocompatible functionally graded coatings intended for medical implants and bone tissue bioengineering applications.

Effect of MgO and Nd₂O₃ doping on the structural characteristics of nickel ferrite NiFe₂O₄

Анна Загребова — 2026-09-30

In this work, the effect of MgO and Nd₂O₃ doping on the structural characteristics of spinel-structured nickel ferrite NiFe₂O₄ synthesized by the sol–gel auto-combustion method was investigated. The synthesized samples were subjected to thermal treatment at 1000 °C, after which their phase composition and crystal lattice parameters were examined using X-ray diffraction analysis.

It was shown that the introduction of MgO in the concentration range of 0.05–0.15 M leads to a decrease in the content of impurity phases Fe₂O₃ and FeO and, at concentrations of 0.10–0.15 M, is accompanied by the formation of a new orthorhombic Mg₂Fe₂O₅ phase characterized by enhanced structural ordering. Doping with Nd₂O₃ ensures complete suppression of impurity iron oxide phases and initiates the formation of the FeNdO₃ phase, which contributes to increased thermal and chemical stability of the spinel matrix. It was established that the combined introduction of MgO and Nd₂O₃ results in changes in the unit cell parameters of the main NiFe₂O₄ phase due to cation substitution processes and defect redistribution, as well as structural ordering of impurity phases within the nanocomposites.

The obtained results confirm the possibility of targeted control over the phase composition and structural stability of spinel-structured nickel ferrite, creating prerequisites for optimizing its functional properties and application in adsorption-based water purification processes.

Humidity sensing properties of carbon nanowall films synthesized by CCP-PECVD

Рахымжан — 2026-09-30

Carbon nanowall (CNW) films were synthesized by capacitively coupled plasma-enhanced chemical vapor deposition and evaluated as active layers for resistive humidity sensing. SEM observations confirmed the formation of vertically oriented CNW sheets, while Raman analysis showed typical defect-related and graphitic carbon bands, confirming the formation of a petal-like carbon nanowall network. Humidity-sensing performance was studied over a relative humidity range of 10–100% at 27, 50, and 75 °C. The fabricated sensors exhibited repeatable electrical responses over short cycling tests and a clear temperature dependence. At 27 °C, the sensor showed the highest sensitivity, reaching 2.27% at 100% RH, with response and recovery times of 87 and 97 s, respectively. Increasing the operating temperature reduced the sensitivity to 0.49% at 50 °C and 0.22% at 75 °C, which can be attributed to enhanced desorption of water molecules from the CNW surface. These findings indicate that transferred CNW films can be considered as simple and inexpensive platforms for humidity monitoring.

Phase composition and microstructural heterogeneity of ancient ceramics from east Kazakhstan: raman spectroscopy, x-ray microtomography and scanning electron microscopy

MURAT KENESSARIN — 2026-09-30

This study presents the results of a comprehensive investigation of ceramic fragments from the Shagantogay archaeological site (Makanchi District, Abay region, Republic of Kazakhstan) using modern non-destructive analytical techniques: Raman spectroscopy, X-ray microtomography, and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS). Raman spectroscopy revealed a heterogeneous mineral composition of the ceramics, comprising quartz, anatase, feldspars, and carbonate phases. X-ray tomographic examination demonstrated significant differences in the internal structure of the ceramic samples, ranging from dense and homogeneous to highly porous with inclusions of organic origin. SEM-EDS data confirmed the variability of elemental composition, which correlates with the identified mineral phases.

Vertical epicyclic stability and dissipative settling in a weakly deformed q-metric spacetime

Ayazhan Orazymbet — 2026-09-30

We investigate the motion of massive test particles close to the equatorial plane of a weakly deformed q-metric spacetime. Working to first order in the dimensionless quadrupole parameter q, we derive the orbital angular velocity and the vertical epicyclic frequency for equatorial circular orbits while keeping the physical monopole mass fixed. The Schwarzschild limit is recovered at q = 0, whereas a nonzero quadrupole removes the degeneracy between the vertical and azimuthal frequencies already at O(q).

A small phenomenological damping term is then introduced into the linearized vertical equation to describe the gradual approach of a perturbed orbit toward the equatorial plane. In the conservative case, the particle continues to oscillate about this plane without any decrease in amplitude. With damping, the amplitude decays exponentially. The quadrupolar deformation changes the vertical oscillation frequency and, consequently, the number of cycles completed before a specified settling threshold is reached. It does not, however, set the decay timescale, which follows from the adopted damping prescription. Since the coordinate-time damping coefficient is kept fixed in our numerical examples, the trajectories share the same exponential envelope but oscillate at different frequencies.

The comparison with the exact q-metric also provides a direct check of the firstorder approximation. Over the sampled domain |q| ≤ 0.1 and 6 ≤ r/M ≤ 20, the relative error in the vertical frequency remains below 0.34%, while the corresponding frequency ratio is reproduced to better than 0.10%. These results show explicitly how the quadrupolar geometry modifies vertical orbital dynamics within a model in which dissipative settling is introduced independently.

Графен оксидімен модификацияланған хитозан негізіндегі биоүйлесімді композиттік трек мембраналарын дайындау және олардың құрылымын, биоүйлесімділігі мен тасымалдау қасиеттерін кешенді зерттеу

Alisher Zhumabayev — 2026-09-30

Хитозан негізінде графен оксидімен (GO) модификацияланған биоыдырайтын композиттік тректік мембраналар дайындалды. SRIM әдісі арқылы ауыр иондармен сәулелендірудің қажетті параметрлері анықталды. Одан кейін химиялық өңдеу жағдайларын оңтайландыру шарттары таңдалып, толық өтетін кеуекті құрылым қалыптастырылды. РФЭС, СЭМ және термогравиметриялық талдау нәтижелері мембраналардың графен оксидімен жақсы модификацияланғанын, тректік кеуектердің түзілгенін және композиттердің термиялық тұрақтылығының артқанын растады. Биоүйлесімділікті зерттеу нәтижесінде 1,0 мг/мл концентрацияда мембрана экстрактыларының жасушалараға деген кері әсері байқалмады. Электрохимиялық импеданстық спектроскопия зерттеуіне сәйкес, графен оксидін қосу мембрананың мембрананың көлемдік кедергісін төмендетіп, иондық өткізгіштігін арттырғаны анықталды. Оның ең жоғарғы мәні GO мөлшері 0,5 масс.%. болған кезде байқалды. Дайындалған мембраналарды толық қатты күйдегі суперконденсаторларға арналған гель-полимерлі электролиттердің матрицалары ретінде қолданудың келешегі зор.

Structure and electrochemical properties of the cathode materials Na3Fe2(PO4)3 and Na3Fe2(PO4)3/C

Артур Ногай — 2026-09-30

This article presents a comparative assessment of the structures and electrochemical properties of Na₃Fe₂(PO₄)₃ and Na₃Fe₂(PO₄)₃/C_x polycrystals obtained by a solid-phase synthesis method. It has been established that, as a result of carbon doping, the structures of α- Na₃Fe₂(PO₄)₃/C_x polycrystals exhibit changes in symmetry and unit cell parameters compared with those of Na₃Fe₂(PO₄)₃. It has been shown that the use of Na₃Fe₂(PO₄)₃/C_x polycrystals as cathode materials in lithium-ion batteries is more effective than that of Na₃Fe₂(PO₄)₃. Moreover, as the concentration of carbon atoms in the Na₃Fe₂(PO₄)₃/C_x cathode materials increases, the specific capacity of the SIB increases, although this is accompanied by a decrease in structural stability during cycling. The use of Na₃Fe₂(PO₄)₃/C_x compositions (0 < x < 0.5) is advisable as cathode materials in SIB, as this improves the battery’s specific capacity whilst ensuring that the structural stability of the cathodes remains at an acceptable level.

PhD Impurity Luminescence and Selective Vacuum-Ultraviolet Excitation in a Nominally Undoped YAlO₃ Crystal

Гулдар Баубекова — 2026-09-30

The emission spectrum of a nominally undoped yttrium aluminate (YAlO₃) single crystal under excitation at 7.75 eV and the excitation spectra of nine emission channels were investigated at 300 K. The measurements were performed at beamline P66 of the PETRA III synchrotron radiation facility at DESY. A combined analysis of the original spectra, normalized dependences, and inter-channel intensity ratios revealed two distinct groups of excitation behavior. The emission channels at 352.6, 465, 523.6, and 794.6 nm exhibit an excitation maximum near 7.85 eV, whereas the 724.4 and 749.4 nm channels are predominantly excited in the 6.8–6.9 eV range and show a correlation coefficient of 0.982.

The 722.7/725.0 nm doublet is assigned to Cr³⁺ ions, while the sequence of lines at 875.5, 884.4, and 891.9 nm, together with a weak group at 915–916 nm, is consistent with the Stark structure of Nd³⁺. For the remaining spectral regions, testable assignments to Tm³⁺, Er³⁺, and other rare-earth centers are proposed without claiming their unambiguous identification. The common excitation behavior of the red emission channels and an energy separation of approximately 462 cm⁻¹ support a possible vibronic origin of the band near 750 nm.

It is shown that the excitation maximum near 7.85 eV alone does not provide sufficient evidence for an excitonic mechanism in the absence of a validated correction for the incident photon flux. The limitations of lamp-based spectroscopy and the conditions required for reliable identification of trace impurities are discussed.