For the first time, translucent NaLa9(GeO4)6O2 ceramics were obtained using thermobaric treatment of polycrystalline oxyapatite. The initial powder of NaLa9(GeO4)6O2 germanate was prepared by the citrate method. High-pressure high-temperature sintering was performed at 8 GPa, 600 degrees C for 10 min. The proposed technology for producing ceramics is unique for germanates and differs from the traditional technology of quenching GeO2 melt used to produce germanium glass-ceramics. Two ways of heat treatment of the initial powder are compared from the point of view of the optical properties of ceramics. It is shown that more transparent ceramics are obtained from a polycrystalline sample with a grain size of 40 nm. The total forward transmittance is 55% at 500 nm and 80% at 1200 nm. The difference in the local structure of the initial polycrystalline phase and NaLa9(GeO4)6O2 apatite ceramics was revealed using EPR for Gd3+ as a paramagnetic probe.

EPR—a high-dose dosimetry method for use in monitoring radiation technologies has been tested for a proton beam with an energy of 18 MeV using a domestic brand of polytetrafluoroethylene as a radiation detector and an original EPR spectrometer. It has been shown that the dose range of the EPR signal is limited to 1.5 MGy, after which saturation occurs. Doses exceeding this value can be measured using additional signals in the EPR spectrum. It was found that irradiation of the detectors makes them gamma radioactive. The energy of the gamma radiation and the half-life of the source corresponded to the isotope 18F obtained in the nuclear reaction 18O(p,n)18F, which indicated the presence of oxygen in the material of detectors, which determines their paramagnetic properties.

The possibility of implementing the high-dose dosimetry method based on a combination of electron paramagnetic resonance (EPR) and thermally stimulated luminescence (TL) phenomena was investigated. Domestically produced polytetrafluoroethylene (PTFE) was used as an ionizing radiation detector. Detector samples were irradiated with accelerated electrons with an energy of 10 MeV with doses from 10 to 50 kGy. After irradiation, the intensities of the EPR and TL signals were measured from each detector. The dependence of the EPR signal intensity on the radiation dose was linear. The TL parameters were equal to: maximum temperature T_m = 164 ^∘C , form factor μ_g = 0.45 , frequency factor S = 4.44 ×10^11 s^ - 1 , activation energy E = 1.14 eV. The spectral composition of TL had a wide band with a luminescence maximum of approximately 425 nm. The dose dependence of the TL output was also linear in the studied dose range. Annealing of EPR and TL signals occurred in the same temperature range, 160–240°C. The correlation of dose dependences of normalized intensities of EPR and TL signals, the similarity of their temperature ranges of annealing intensities, indicated that the EPR and TL properties of PTFE detectors are associated with changes in the charge states of the same centers.

Both pristine and Eu3+-doped scandium-potassium complex sulfate KSc(SO4)(2) has been obtained with 99% yield via crystallization from solutions. The high-temperature XRPD and thermal studies revealed an enantiotropic first-order phase transition at 700-725 K and standard pressure. In the temperature region 724-754 K, the low-temperature stable monoclinic polymorph, beta-KSc(SO4)(2) (sp.gr. & Scy;2/m), coexists with the high-temperature trigonal modification, alpha-KSc(SO4)(2) (sp.gr. P321), with decomposition at similar to 1120 K. DFT calculations confirmed this rank of polymorphs and a low hospitality of their Sc-sublattices for Eu3+ cations. Under UV excitation, the KSc0.98Eu0.02(SO4)(2) sample exhibits Eu3+ luminescence at 570-720 nm. Heating of the sample from 298 K to 423 K leads to a luminescence fading of 13% and to its a sharp decline at elevated temperatures. Kinetic studies have shown that the lifetime depends on the chosen excitation wavelength and temperature. An & KHcy;-band resonance in the sample of KSc(SO4)(2):Eu3+ has been detected in the temperature range of 299-500 K. The EPR spectra are interpreted assuming the presence of sulfate radicals.

In the Y2SiO5 single crystal doped with iron, transitions of three triclinic Fe3+ centers localized in silicon positions were detected near g = 4.3. The positions of these transitions weakly depend on the orientation of the magnetic field. The orientation behavior of other transitions of these centers has been studied. The parameters of the constructed spin Hamiltonians of two of them in the main axes satisfy the conditions: b(2)(0)- D is close to b(2)(2)- 3E while b(2)(0) >> g beta B. These centers can be attributed to Fe3+ ions localized in silicon positions and compensated for both locally and non-locally by oxygen vacancies.

The EPR spectra of Czochralski grown Y2SiO5:Cr and Y2SiO5:53Cr crystals have been studied. In addition to the previously known spectra of Cr3+, the spectrum of the Cr4+ ion was detected and studied for the first time. The fine structure parameters of tetravalent chromium in Y2SiO5 host were obtained based on the analysis of the angular and frequency-field dependences of the EPR spectra. The conclusion about tetrahedral coordination of Cr4+ ion in this host was made. The concentrations ratio of c(Cr3+)/c(Cr4+) ions in the crystal has been evaluated.

The study of grown Sc 2 SiO 5 : Gd and Sc 2 SiO 5 : Fe crystals was carried out by the paramagnetic resonance method. It has been established that Fe 3+ ions replace Sc 3+ in both crystallographic positions, while Gd 3+ ions exhibit a single center localized in a larger position with a coordination number of 7. Measurement of the orientational behavior of the positions of transitions of Fe 3+ and Gd 3+ centers in two orthogonal planes made it possible to determine the parameters of their triclinic spin Hamiltonians. To determine the localization of impurity ions Cr 3+ , Fe 3+ and Gd 3+ in scandium and yttrium silicates, the orientation of the main Z axes of the fine structure tensors of the second rank was used. Keywords: scandium and yttrium silicates, impurity ions, paramagnetic resonance.

In this article, the possibilities of recording EPR spectra by the non-adiabatic rapid sweep (NARS) method on a superheterodyne spectrometer are investigated. This method allows recording the pure EPR absorption spectrum of the object under investigation without the need for lineshape-lineheight compromise, while increasing sensitivity by suppressing low-frequency noise. In the NARS method, a low-amplitude sinusoidal modulation of a magnetic field is not used, and an oscillating triangular-shaped bipolar magnetic field is superimposed on the main permanent magnetic field. The triangular field repetition rate should be higher than that of the undesirable noise, and the amplitude is such that the rate of field change satisfies the Bloch non-adiabaticity criterion. The EPR absorption signal is digitized by a fast ADC and accumulated over a large number (n) of triangular field periods. In this case, for low-frequency noise, the spectrum of which is located below the repetition frequency of the triangular field, an accumulation process occurs with an increase in the signal-to-noise ratio (SNR) in proportion to n. A remarkable property of a superheterodyne spectrometer is that the frequency below which low-frequency noise prevails over white noise is significantly lower for it than for a homodyne spectrometer. This allows the use of a low repetition rate (LF NARS), which makes it much easier to obtain a highly linear triangular field of significant amplitude even in microwave resonators with a massive metal case since the harmful effects of eddy currents are reduced. The conditions of non-adiabaticity become easily feasible. At the same time, the noise suppression effect during accumulation turns out to be so significant that the SNR of the LFNARS spectrum exceeds that of the traditional spectrum with magnetic field modulation, with the same recording time, by more than 10 times.

The orientation behavior of the EPR-transitions of uncontrolled V 4+ (S=1/2) and Fe 3+ (S=5/2) impurity centers in a Na 5 AlF 2 (PO 4 ) 2 single crystal doped with chromium has been studied. The parameters of the spin Hamiltonian of these centers are determined both in the laboratory (crystallographic) and in the local coordinate systems. Based on the fact of the existence of mixed vanadate-phosphates and taking into account the orientation of the principal axis V 4+ , it was concluded that vanadium replaced the position of phosphorus. The closeness of the principal axes of the fine structure tensors of the second and fourth ranks of Fe 3+ centers to the F-F direction of the fluorine-oxygen octahedron surrounding the iron ion was found. Keywords: impurity ions, paramagnetic resonance, hyperfine interaction.

The article presents a Hall effect magnetometer for use in a desktop Electron Paramagnetic Resonance spectrometer with a permanent magnet system and scanning coils. High accuracy and long-term stability at a small size and low cost are achieved through the use of digital signal processing, sequential data filtering in the time and frequency domains, as well as digital correction of raw data based on calibration information. The exciting current of the Hall sensor has the form of an alternating-sign square wave formed by a high-speed H-bridge powered by a stable direct current. Generation of control signals, time selection of data, and their accumulation are performed using Xilinx Field-Programmable Gate Array Artix-7. MicroBlaze embedded 32-bit processor is used to control the magnetometer and interface with adjacent levels of the control system. Taking into account the individual characteristics of the sensor, including the offset voltage, the nonlinearity of the magnetic sensitivity, and their temperature dependences, is carried out by correcting the data obtained by calculating a polynomial depending on the raw magnitude of the field induction and the temperature of the sensor. The polynomial coefficients are individual for each sensor, are determined once during the calibration process, and are stored in the dedicated Electrically Erasable Programmable Read-Only Memory. The magnetometer has a high resolution of 0.1 µT and an absolute measurement error of not exceeding 6 µT.

The orientation behavior has been investigated for previously non-studied signals in the EPR spectra of the 53Cr:Y2SiO5 crystal grown by Czochralski method. These signals are assigned to two Gd3+ centers replacing yttrium ions in two physically nonequivalent triclinic sites. The spin Hamiltonian (SH) parameters have been determined both in the laboratory and in local coordinate systems, in which the second-rank fine structure tensor becomes diagonal.

An intense electron paramagnetic resonance (EPR) spectrum has been unexpectedly observed at room temperature in polycrystalline samples of NaYGeO4 with olivine crystal structure. Signals were registered in a wide range of fields up to 6000 G. Along with strongly broadened unresolved resonance lines, the relatively narrow spectral components were found. It is shown that the spectrum profile depends on synthesis conditions and mechanical treatment of samples, all suggesting a partial orientational order of microcrystallites in the powders. The spectra are interpreted under the assumption of strong superhyperfine interaction between the oxygen-deficient centers like [GeO3](3-)and the nuclei of Na+ cations. In addition, a sharp anisotropic resonance at g-values exceeding free -electron value is attributed to oxygenic-hole centers. The density functional theory (DFT) calculations are employed for the estimation of the thermodynamic stability of various intrinsic defects.

The paramagnetic resonance of Na5AlF2(PO4)2 single crystals with chromium impurity was studied. The Cr3+ centers have been found to replace the triclinic Al3+ positions. In the local coordinate system, the spectra of these centers were described by the spin Hamiltonian of rhombic symmetry. In addition, vanadium centers and unidentified triclinic symmetry centers have been observed. Keywords: impurity ions, aluminum fluoride phosphate, paramagnetic resonance.

The EPR spectrum of single crystals of scandium orthosilicate doped with chromium was studied in the X-band. In the crystallographic and local coordinate systems, the parameters of the spin Hamiltonians of two Cr3+ centers that have replaced scandium in the nonequivalent triclinic positions and demonstrate orthorhombic symmetry in the principal axes are determined. The spectrum of the Gd3+ center localized in one of scandium position was discovered and studied, and the parameters of the fine structure of its ground state were determined. In the studied crystals, EPR signals of unidentified paramagnetic centers also were observed. Keywords: scandium orthosilicate, impurity ions, paramagnetic resonance.

This article describes a desktop X-band superheterodyne spectrometer designed to measure EPR spectra in the vicinity of g = 2. The spectrometer operates in the vicinity of the 9.2 GHz frequency in the power range of about 40 mW-1 nW. The device uses Time Locking concept with digital quadrature detection of intermediate frequency (100 MHz) and the synthesis of all signals used in the device from a single driving oscillator. To register CW spectra, a TE 102 rectangular cavity with the capability of matching and frequency tuning is used. The microwave part of the spectrometer is implemented in the form of two non-tunable modules based on microstrip technology and commercially available microwave MMICs. Two modes of operation are provided - both with PLL of microwave sources with a highly stable driving oscillator as a reference and an AFC system without frequency modulation. All signal processing after digitization of the intermediate frequency is performed digitally using FPGA resources. It is possible to record EPR spectra both with magnetic field modulation at various frequencies and without modulation. The bandwidth of the receiving path can be selected from the widest 46 MHz to about 1.5 kHz, which allows the spectrometer to be used both for recording weak signals and for recording fast-flowing processes. The spectrometer uses a magnetic system on permanent magnets Sm-Co with magnetic field uniformity of about 3 * 10 (5). Changing the magnetic field in permanent magnets is done using scanning coils which provides a field change of >800 G (p-p). The control of the magnetic field induction in the magnet gap is performed by a specially designed precision Hall effect magnetometer, which provides a resolution of 1 mG with an absolute error of no more than 0.2 G. A personal computer for spectrometer control is connected via Ethernet. The spectrometer is stable and easy to use. The high performance of the spectrometer is confirmed by the recorded spectra. (C) 2022 Elsevier Inc. All rights reserved.

The optical absorption and electron paramagnetic resonance (EPR) spectra were investigated in Czochralski grown Y2SiO5 single crystal doped by 53Cr isotope. For the first time, EPR signals of Cr3+ ions localized in two physically non-equivalent yttrium positions were detected in this crystal. The parameters of the fine and hyperfine structures of the observed centers have been determined.

EPR spectra of impurity ions of Mn2+ (S = 5/2), Gd3+ (S = 7/2), and Cu2+ (S = 1/2) were found and investigated in addition to the intensive signals of axial centers of Cr4+ in the Li2CaSiO4 crystal. Manganese and gadolinium ions show spectra of tetragonal symmetry; copper ions show both spectra of axial and triclinic symmetry. Parameters of the spin Hamiltonians for the tetragonal centers were determined. Ions of Mn2+ and Gd3+ were shown to replace calcium ions with octahedral oxygen environment; copper ions are localized on lithium positions having tetrahedral environment. The reasons for appearing of triclinic Cu2+ centers are discussed.

EPR spectra of impurity ions of Mn 2+ ( S = 5/2), Gd 3+ ( S = 7/2), and Cu 2+ ( S = 1/2) were found and investigated in addition to the intensive signals of axial centers of Cr 4+ in the Li 2 CaSiO 4 crystal. Manganese and gadolinium ions show spectra of tetragonal symmetry; copper ions show both spectra of axial and triclinic symmetry. Parameters of the spin Hamiltonians for the tetragonal centers were determined. Ions of Mn 2+ and Gd 3+ were shown to replace calcium ions with octahedral oxygen environment; copper ions are localized on lithium positions having tetrahedral environment. The reasons for appearing of triclinic Cu 2+ centers are discussed.

Rhombic 153 Eu 2+ and 151 Eu 2+ centers are studied in specially grown single crystals of yttrium–aluminum garnet. The parameters of the hyperfine and quadrupole interactions describing the hyperfine structure of the EPR spectra of both isotopes have been determined.

Investigation of the EPR spectrum of Y3Al5O12:V crystals have made it possible to determine the parameters of the fine and hyperfine structures of trigonal V2+ centers. The existence of V2+ triclinic centers that arise as a result of association of V2+ sites with defects that lower the symmetry is established.