Optically transparent nanoceramics of the composition Mg1-xMnxAl2O4(x = 0.005) with a grain size of 15–40 nm were obtained by thermobaric synthesis in a toroid-type high-pressure chamber in the range P = 4–9 GPa at a temperature of 600°C. EPR spectroscopy indicates the presence of divalent manganese ions with a characteristic HFS signal. In addition, the signal from F+ centers were registered in the EPR spectrum. It has been established that in the HFS of impurity Mn2+ there is an additional contribution from manganese centers split in the field of rhombic symmetry. Photoluminescence spectroscopy methods revealed the presence of optically active centers based on Mn3+ and Mn4+. With an increase in the synthesis pressure, the conversion of manganese ions localized in octa- and tetra- positions occurs, accompanied by a change in valence. It has been found that some manganese ions with a valence of 2+ can be localized in an octahedral oxygen environment, occupying anti-site positions with reduced point symmetry. The formation of F-type centers, as well as polyvalent manganese centers, was confirmed by the cathodoluminescence method. Changing the synthesis parameters makes it possible to control the ratio of valence manganese ions in the corresponding sites of the spinel crystal lattice, thereby expanding the methodological base of defect nanoengineering.

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 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.

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.

Исследовано ориентационное поведение ЭПР-переходов неконтролируемых примесных центров V4+ (S=1/2) и Fe3+ (S=5/2) в монокристалле Na5AlF2(PO4)2, легированном хромом. Определены параметры спинового гамильтониана этих центров как в лабораторной (кристаллографической), так и в локальной системах координат. Основываясь на факте существования смешанных ванадат-фосфатов и учитывая ориентацию главной оси V4+ сделан вывод о замещении ванадием позиции фосфора. Обнаружена близость главных осей тензоров тонкой структуры второго и четвертого ранга центров Fe3+ к направлению F-F фтор-кислородного октаэдра, окружающего ион железа. Ключевые слова: примесные ионы, парамагнитный резонанс, сверхтонкое взаимодействие.

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 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.

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 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.

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.

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.

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.

In the Li2CaSiO4 crystal, in addition to intense axial centers of Cr4+, the EPR spectra of impurity ions Mn2+ (S = 5/2), Gd3+ (S = 7/2), and Cu2+ (S = 1/2) have been discovered and studied. Manganese and gadolinium ions exhibit spectra of tetragonal symmetry, copper ions are represented by spectra of both axial and triclinic symmetry. The parameters of the spin Hamiltonians of tetragonal centers are determined. It was shown that Mn2+ and Gd3+ ions substitute for calcium ions with an eightfold oxygen environment, copper ions are localized in lithium positions with a tetrahedral environment. The reasons for the appearance of Cu2+ triclinic centers are discussed.

We report on the results of analysis of optical absorption, EPR signals under optical excitation and magnetic susceptibility of hydrothermal Zn 1 – x Mn x O single crystals. In the absorption spectra of polarized light at temperatures of 4.2 and 77.3 K, narrow intense a , b , c , and d lines are observed in the energy range 1.877–1.936 eV of light quanta. The spectrum of these lines differs significantly from the spectra of donor and acceptor excitons for ZnO:Co and ZnO:Ni. The intensity of allowed and forbidden EPR signals of the Mn 2+ ( d 5 ) ions does not change under the action of light in the impurity absorption band, while the EPR signals of uncontrollable Fe 3+ ( d 5 ) ions under illumination practically disappear. New experimental results for Zn 1 – x Mn x O lead to the conclusion that the d 5 / d 4 donor level of the Mn 2+ ion falls into the valence band, while the bandgap of Zn 1 – x Mn x O contains several dangling bond hybrid (DBH) states due to hybridization of 3 d orbitals of the Mn 2+ ion with the p -bonds of the nearest O 2– oxygen ions. Electron transitions from the DBH states to the conduction band form a broad impurity absorption band of Zn 1 – x Mn x O, below the edge of which the a , b , c , and d lines referred to as donor excitons [( h loc + d 5 ) e ] and emerging as a result of Coulomb interaction of a free s -electron and a hole localized on DBH states ( p + d 5 ) are observed. The detection of donor excitons [( h loc + d 5 ) e ] makes it possible to study in detail the DBH states in the bandgap, which is important for photocatalysis in the visible light range.

The fine and hyperfine structures of the paramagnetic resonance spectrum of the trigonal Cr3+ centers in the chromium-doped Pb5Ge3O11 samples after annealing at low oxygen pressure have been studied. The localization of chromium ions in the lead germanate crystal lattice, as well as the results of studying the effect of such doping on the susceptibility of crystals to the second harmonic are discussed.

Nanoceramics of Mg1-xMnxAl2O4; x=0.005, 0.00005 was obtained using thermobaric synthesis method. As a result of an increase in the concentration of impurity manganese, the impurity is redistributed over cationic positions, which stimulates lattice compression. The stabilization of the Mn2+ and Mn3+ states was discovered, due to the relatively low temperatures of thermobaric synthesis (not more than 600 °C). It is shown that impurity manganese ions in nanoceramics can act as indicators of structurally nonequivalent tetra- and octahedral positions.

In crystals of yttrium orthoaluminate doped with the 151 Eu isotope, Eu 2+ , Cr 3+ , Gd 3+ , and Мо 3+ paramagnetic centers are detected. The fine structure parameters of the spin Hamiltonian are determined or refined for these centers. The orientation behavior of previously unobserved forbidden transitions is considered for the Cr 3+ centers. It is shown that two Mo 3+ signals that are detected in magnetic fields directed parallel to the crystallographic axes do not belong to different molybdenum centers, but are two intradoublet transitions of the same center.

Using experimental second-rank parameters of the spin Hamiltonian of the rhombic centers Gd 3+ and Eu 2+ in three garnets and the superposition approximation formalism, relaxation of the nearest environment of impurity ions is estimated.