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.

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.

In this paper photoluminescense spectra and EPR-signals of ZnO single crystals, doped with manganese and containing (from EPR data) uncontrolled impurity of iron, were investigated. At the temperature of 4.5 K in photoluminescense spectrum the band in energy interval of 1.55-1.8 eV (12493 – 14508 cm-1) was observed. This band contains some intensive lines; these lines are caused by Fe3+ ions (d5-configuration). The first and most intensive line at the energy of 1.79 eV corresponds to irradiative transition 4T1 (G) → 6A1 (S) in Fe3+ ions. The other peaks are electronic-vibrational structure. This structure may be caused by force interaction in deformed Fe3+ - 4O2- - cluster.

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.

In specially grown single crystals of yttrium-aluminum garnet, the orthorhombic centers 153Eu2+ and 151Eu2+ were investigated. The parameters of hyperfine and quadrupole interactions, which describe the hyperfine structure of the EPR spectrum of both isotopes, are determined.

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.

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.

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.

The study of the EPR spectrum of Y3Al5O12:V crystals allowed us to determine the parameters of the fine and hyperfine structure of the V2+ trigonal centers. The existence of V2+ triclinic centers that arose as a result of association of V2+ with defects that reduce symmetry was discovered.

Tetragonal Cr4+ centers (3d2 electron configuration, spin S=1) in the Li2CaSiO4 crystal at different frequencies were detected and studied. The value of splitting at a zero magnetic field was determined. In the area where the positions of the two Cr4+ transitions coincide, the additional signal with inverse phase was observed. For uncontrolled impurity Mn2+ ions (S=I=5/2) the spin Hamiltonian parameters and localization are determined