A. P. Potapov

High-spin europium and gadolinium centers in yttrium–aluminum garnet

Electron-spin resonance spectra of Eu2+ and Gd3+ centers substituting Y3+ ions in single-crystal yttrium–aluminum garnet have been studied and the parameters of their rhombic spin Hamiltonian have been determined. The fine-structure parameters of the above ions have been calculated in the superposition model disregarding changes in the angular coordinates of the ligand environment of the impurity defect thus demonstrating the necessity of taking these changes into account.

Trigonal and triclinic Fe3+ paramagnetic centers in ferroelectric Pb5Ge3O11

In the EPR spectra of iron-doped lead germanate single crystals, triclinic Fe3+ paramagnetic centers have been found in addition to trigonal centers. Their contribution increases upon annealing in a chlorine-containing atmosphere. The parameters of the spin Hamiltonian of three triclinic centers assigned to Fe3+-Cl− dimeric complexes have been determined. The localization of iron and chlorine ions in Pb5Ge3O11 has been discussed.

Paramagnetic resonance of yttrium aluminum garnet doped with 151Eu2+ ions

The 151Eu2+ orthorhombic centers in yttrium aluminum garnet crystals have been investigated. The initial splitting and hyperfine interaction parameters have been obtained taking into account the positions of the hyperfine structure components. The relative signs of the fine and hyperfine structure parameters have been determined from the analysis of the type of the hyperfine structure formed by the allowed and forbidden electron–nuclear transitions.

Gd3+-F− dimer centers in the ferroelectric lead germanate

The Gd3+ centers formed in lead germanate doped with fluorine have been studied using electron paramagnetic resonance. The parameters of the triclinic spin Hamiltonian are found at room temperature. The center is shown to be a gadolinium ion having the nearest environment in which the fluorine ion is substituted for the oxygen ion. The Gd-F dimer binding energy relative to the energy of a single gadolinium ion is determined. The interaction of the dimer center with the spontaneous polarization is lower than the measurement error.

Paramagnetic defects in ZnSe crystals doped with iron ions

The electron paramagnetic resonance (EPR) spectra of iron-doped ZnSe single crystals were studied. In addition to cubic Fe3+ and Mn2+ centers and also Fe2+, and Cr2+ centers, monoclinic Fe3+ complexes locally compensated by Cu+ ions were revealed. Some trigonal centers with a spin of 3/2 were also found and studied. The zero-field splittings of monoclinic centers were measured, and the parameters of the monoclinic and trigonal spin Hamiltonians were determined. The nature of trigonal centers was discussed.

Paramagnetic defects in manganese-doped lead tungstate

In manganese-doped PbWO4 crystals, low-intensity signals of triclinic clusters Mn4+-VO and Fe3+-VPb have been revealed in addition to signals of Mn2+ tetragonal centers. The Mn4+-VO cluster is formed by a Mn4+ ion in the W6+ position, which is associated with a vacancy of the nearest neighbor O2−ion, and the Fe3+-VPb cluster consists of a Fe3+ ion substituting for Pb2+ with a local compensation of by a lead vacancy. It has been shown that, in PbWO4: Mn, there is also a small amount of Mn4+ tetragonal centers located in the Pb2+ position with a nonlocal compensation of an excess charge.

Electron paramagnetic resonance of Gd3+ ions in Ca1 − x − yYxGdyF2 + x + y crystals

Electron paramagnetic resonance of Ca1 − x − yYxGdyF2 + x + y single crystals has revealed spectra that are not typical of gadolinium-doped CaF2 crystals. These spectra have a nearly tetragonal symmetry and are most probably caused by Gd3+ ions localized in yttrium clusters. Weak spectra of tetragonal Gd3+ centers, whose parameters are close to those of a cubic gadolinium center caused by an isolated Gd3+ ion, have been also detected. These centers are attributed to isolated Gd3+ ions localized near octahedral rare-earth clusters or their associations.

Photosensitive bismuth ions in lead tungstate

Electron paramagnetic resonance (EPR) signals of Bi2+ ions have been detected in the EPR spectrum of manganese-, bismuth-, and tin-doped PbWO4 single-crystals irradiated by xenon and mercury lamps at 100 K. The parameters of the Zeeman, hyperfine, and superhyperfine interactions and the localization of Bi2+ ions have been determined.

Paramagnetic Complexes in Zinc Selenide Crystals with Iron Admixture

Paramagnetic resonance of ZnSe: Fe single crystals was studied at 120 K. Parameters of the spin Hamiltonian were determined for the monoclinic dimer complex Fe3+–Cu+ and a second discovered Fe3+ center, which appears due to association of the iron ion with a K+ ion in a Zn2+ position or with a zinc vacancy. Effect of illumination of the zinc selenide samples by blue, green and red light on the paramagnetic resonance spectrum was investigated.

Relaxation of the environment of Gd3+ and Eu2+ impurity ions in the Y3Al5O12 garnet

The second-rank spin Hamiltonian parameters of Gd3+ and Eu2+ orthorhombic centers in crystals of the yttrium aluminum garnet Y3Al5O12 have been analyzed within the framework of the superposition model for the zero-field splitting of the ground state. It has been shown that the description of the experimental data in this model is possible only under the assumption of relaxation of the ligand environment of the paramagnetic impurity.