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© 2016 Elsevier B.V.The EPR spectrum of the Ce3+ ion in the crystal of the elpasolite type Rb2NaYF6 has been observed and studied at low temperatures (Т = 4.2 – 80 K). It was established that the paramagnetic center Ce3+ has tetragonal symmetry confirming the experimental fact we reported recently that at low temperatures the Rb2NaYF6 crystal exists in the tetragonal phase, into which it transferred from the cubic phase as a result of the structural phase transition (PT). Parameters of the spin Hamiltonian of the tetragonal EPR spectrum were determined. A scheme of 4f energy levels of the Ce3+ ion in Rb2NaYF6 before and after PT was proposed from the theoretical interpretation of the observed g-factors and parameters of the crystal fields acting on it were determined.

An attachment for an optical spectrometer is described enabling automated measurements of the impurity distribution in a crystal. For analysis of the Nd3+ ion distribution over a LiYF4 crystal, it is shown that the attachment provides a high resolution when obtaining data on the optical quality of a crystal and the impurity concentration profile and reliably determines the impurity distribution coefficient. © 1997 MAEe cyrillic signK Hayκa/Interperiodica Publishing.

© 2016 Elsevier B.V.The EPR spectrum of the Ce3+ ion in the crystal of the elpasolite type Rb2NaYF6 has been observed and studied at low temperatures (Т = 4.2 – 80 K). It was established that the paramagnetic center Ce3+ has tetragonal symmetry confirming the experimental fact we reported recently that at low temperatures the Rb2NaYF6 crystal exists in the tetragonal phase, into which it transferred from the cubic phase as a result of the structural phase transition (PT). Parameters of the spin Hamiltonian of the tetragonal EPR spectrum were determined. A scheme of 4f energy levels of the Ce3+ ion in Rb2NaYF6 before and after PT was proposed from the theoretical interpretation of the observed g-factors and parameters of the crystal fields acting on it were determined.

An attachment for an optical spectrometer is described enabling automated measurements of the impurity distribution in a crystal. For analysis of the Nd3+ ion distribution over a LiYF4 crystal, it is shown that the attachment provides a high resolution when obtaining data on the optical quality of a crystal and the impurity concentration profile and reliably determines the impurity distribution coefficient. © 1997 MAEe cyrillic signK Hayκa/Interperiodica Publishing.

The results of an electron-nuclear double resonance study of the cubic paramagnetic Yb3+ center in Cs2 NaY F6 and CsCa F3 single crystals are presented. The values and signs of the transferred hyperfine interaction (THFI) parameters for several neighboring shells are determined. It is found that the relevant parameters for the two studied matrices differ, in spite of the fact that the nearest environment of the rare earth ion is nearly identical. A first-principles theoretical analysis is performed for the THFI parameters of the first coordination shell of F- ions. Several mechanisms of metal ion-ligand coupling are considered and it is found that one of them, ligand polarization, explains the difference observed for the THFI parameters in Cs2 NaY F6 and CsCa F3. © 2009 The American Physical Society.

The structural phase transition has been observed for the first time in the Rb2NaYF6 crystal and studied by EPR and optical spectroscopy. EPR spectra of Dy3+ and Yb3+ ions present as unintentional dopants in the nominally undoped crystal and forming tetragonal paramagnetic centers have been identified. A characteristic splitting of some optical lines has been observed in the temperature dependence of the Yb3 + optical spectra. It indicates the splitting of the cubic quartet energy levels of Yb3+ ions by the tetragonal crystal field. The empirical schemes of the energy levels for cubic and tetragonal paramagnetic centers of Yb3+ ions have been established and parameters of the corresponding crystal fields have been determined. The latter have been used for analyzing the crystal lattice distortions occurring in the vicinity of the Yb3+ ion during the phase transition. It has been established using the superposition model that the nearest octahedral environment of the Yb3 + ion is distorted as follows: the fluorine ions are rotated by the angle of 2.1 around the fourfold axis; the F- ions located symmetrically in the plane perpendicular to the rotation axis approach the dopant by 0.0014 nm, whereas the F- ions located on the rotation axis move away by 0.0028 nm. It has been concluded that the studied phase transition includes the critical rotations of the octahedral F groups and noncritical displacement of atoms in the rotated fluorine octahedra. © 2013 American Physical Society.

CsCaF3 crystals doped with Yb3+ ions have been studied using the electron paramagnetic resonance and optical spectroscopy methods. Several types of paramagnetic Yb3+ centers were found, among which a paramagnetic center in the unusual position was established. The parameters of the corresponding spin Hamiltonians and schemes of the energy levels of the observed centers were determined. © 2014 Springer-Verlag Wien.

A trigonal Yb3+ paramagnetic center in the CsCaF3 single crystal was studied by magnetic resonance and optical spectroscopy methods. The structural model of the complex and the empirical energy level scheme were established. The transferred hyperfine interaction parameters and the crystal field ones were determined. The crystal field parameters were used to analyze the lattice distortions in the vicinity of Yb3+ using the superposition model. © 2010 Springer-Verlag.

© Published by Elsevier Ltd. The paramagnetic center of tetragonal symmetry formed by the Yb3+ ion in the KZnF3 crystal has been studied using methods of EPR, ENDOR and optical spectroscopy. The location of the impurity ion and the structural model of the complex differing from the model of the Yb3+ center in KMgF3 have been established. The empirical scheme of the energy levels of the Yb3+ ion has been found. The parameters of its interaction with the crystal electrostatic field and the hyperfine interaction with ligands of the nearest environment have been determined. The parameters of the crystal field were used for the analysis of the distortions of the crystal lattice in the vicinity of Yb3+. The parameters of the transferred hyperfine interaction have been calculated for the distances between Yb3+ and F- ions of the nearest environment obtained taking into account the found distortions. They are in good agreement with the experimental values.

Paramagnetic Tm 2+ ion centers in the KMgF 3 single crystal have been studied by electron paramagnetic resonance and optical spectroscopy. The Stark level energies of the cubic Tm 2+ multiplets have been established from the luminescence spectra and the crystal field parameters have been calculated. Information about the phonon spectra of KMgF 3 crystals has been obtained from the electron-vibrational structure of the optical luminescence spectra. © 2012 Elsevier B.V. All rights reserved.

Electron paramagnetic resonance, electron-nuclear double resonance, and optical spectroscopy of the tetragonal Yb3+ center in KMgF3 are reported here. The results of these experiments allow us to conclude that a previously given structural model as well as the interpretation of the optical spectrum of this center are incorrect. A model is presented and experimentally and theoretically justified. In particular, the values of the hyperfine and transferred hyperfine interaction parameters were determined as well as an experiment-based energy-level scheme. Its parametrization is performed by including simultaneously the crystal field and the spin-orbit interaction within the 7F term. Furthermore, a theoretical analysis of the transferred hyperfine interaction (THFI) parameters is presented. It is further shown from optics and from microscopic calculations of the THFI parameters that g∥ and g⊥ have opposite signs and that the rule of correspondence between the cubic g factor and g̃=1/3 (gx+gy+gz) does not depend on the relative magnitude of the cubic and low-symmetry crystal field acting on the rare-earth ion. ©2000 The American Physical Society.

CaF2 crystals doped with Yb3+ ions have been studied by electron paramagnetic resonance (EPR) and optical spectroscopy. EPR spectra of paramagnetic centers (PCs) for cubic (Tc) and tetragonal (T tet) symmetries were identified. Empirical energy level diagrams were established and crystal field parameters were determined. Information on the CaF2:Yb3+ phonon spectra was obtained from the electron-vibrational structure of the optical spectra. The crystal field parameters were used to analyze the crystal lattice distortions in the vicinity of the Yb3+ ion. Within the framework of a superposition model, it is established that four F- ions located symmetrically with respect to the fourfold axis from the side of the ion-compensator approach the impurity ion and deviate from the PC axis. The second set of four fluorine ions also approaches the Yb3+ ion and the PC axis. The ion-compensator F - also approaches considerably the impurity ion.

Yb3+ paramagnetic center of trigonal symmetry in CaF2 and SrF2 and SrF2 single crystals was studied using electron paramagnetic resonance and optical spectroscopy. Stark level energies of the Yb3+ multiplets were established from absorption, luminescence and excitation luminescence spectra and crystal field parameters were calculated. It was found that the obtained crystal field parameters decreased as the lattice constant increased.

SrF2 and BaF2 crystals, doped with the Yb3+ ions, have been investigated by electron paramagnetic resonance and optical spectroscopy. As-grown crystals of SrF2 and BaF2 show the two paramagnetic centres for the cubic (Tc) and trigonal (T4) symmetries of the Yb3+ ions. Empirical diagrams of the energy levels were established and the potentials of the crystal field were determined. Information was obtained on the SrF2 and BaF2 phonon spectra from the electron-vibrational structure of the optical spectra. The crystal field parameters were used to analyse the crystal lattice distortions in the vicinity of the impurity ion and the F- ion compensating for the excess positive charge in T4. Within the frames of a superposition model, it is shown that three F- ions from the nearest surrounding cube, located symmetrically with respect to the C3 axis from the side of the ion-compensator, approach the impurity ion and cling to the axis of the centre when forming T4. The F- ion located on the axis of the centre between the Yb3+ ion and ion-compensator, also approaches close to the impurity ion.

CsCaF3 crystals doped with Yb3+ ions have been studied using the electron paramagnetic resonance and optical spectroscopy methods. Several types of paramagnetic Yb3+ centers were found, among which a paramagnetic center in the unusual position was established. The parameters of the corresponding spin Hamiltonians and schemes of the energy levels of the observed centers were determined. © 2014 Springer-Verlag Wien.

CaF2 crystals doped with Yb3+ ions have been studied by electron paramagnetic resonance (EPR) and optical spectroscopy. EPR spectra of paramagnetic centers (PCs) for cubic (Tc) and tetragonal (T tet) symmetries were identified. Empirical energy level diagrams were established and crystal field parameters were determined. Information on the CaF2:Yb3+ phonon spectra was obtained from the electron-vibrational structure of the optical spectra. The crystal field parameters were used to analyze the crystal lattice distortions in the vicinity of the Yb3+ ion. Within the framework of a superposition model, it is established that four F- ions located symmetrically with respect to the fourfold axis from the side of the ion-compensator approach the impurity ion and deviate from the PC axis. The second set of four fluorine ions also approaches the Yb3+ ion and the PC axis. The ion-compensator F - also approaches considerably the impurity ion.

The structural phase transition has been observed for the first time in the Rb2NaYF6 crystal and studied by EPR and optical spectroscopy. EPR spectra of Dy3+ and Yb3+ ions present as unintentional dopants in the nominally undoped crystal and forming tetragonal paramagnetic centers have been identified. A characteristic splitting of some optical lines has been observed in the temperature dependence of the Yb3 + optical spectra. It indicates the splitting of the cubic quartet energy levels of Yb3+ ions by the tetragonal crystal field. The empirical schemes of the energy levels for cubic and tetragonal paramagnetic centers of Yb3+ ions have been established and parameters of the corresponding crystal fields have been determined. The latter have been used for analyzing the crystal lattice distortions occurring in the vicinity of the Yb3+ ion during the phase transition. It has been established using the superposition model that the nearest octahedral environment of the Yb3 + ion is distorted as follows: the fluorine ions are rotated by the angle of 2.1 around the fourfold axis; the F- ions located symmetrically in the plane perpendicular to the rotation axis approach the dopant by 0.0014 nm, whereas the F- ions located on the rotation axis move away by 0.0028 nm. It has been concluded that the studied phase transition includes the critical rotations of the octahedral F groups and noncritical displacement of atoms in the rotated fluorine octahedra. © 2013 American Physical Society.

© Published by Elsevier Ltd. The paramagnetic center of tetragonal symmetry formed by the Yb3+ ion in the KZnF3 crystal has been studied using methods of EPR, ENDOR and optical spectroscopy. The location of the impurity ion and the structural model of the complex differing from the model of the Yb3+ center in KMgF3 have been established. The empirical scheme of the energy levels of the Yb3+ ion has been found. The parameters of its interaction with the crystal electrostatic field and the hyperfine interaction with ligands of the nearest environment have been determined. The parameters of the crystal field were used for the analysis of the distortions of the crystal lattice in the vicinity of Yb3+. The parameters of the transferred hyperfine interaction have been calculated for the distances between Yb3+ and F- ions of the nearest environment obtained taking into account the found distortions. They are in good agreement with the experimental values.

Paramagnetic Tm 2+ ion centers in the KMgF 3 single crystal have been studied by electron paramagnetic resonance and optical spectroscopy. The Stark level energies of the cubic Tm 2+ multiplets have been established from the luminescence spectra and the crystal field parameters have been calculated. Information about the phonon spectra of KMgF 3 crystals has been obtained from the electron-vibrational structure of the optical luminescence spectra. © 2012 Elsevier B.V. All rights reserved.

The results of an electron-nuclear double resonance study of the cubic paramagnetic Yb3+ center in Cs2 NaY F6 and CsCa F3 single crystals are presented. The values and signs of the transferred hyperfine interaction (THFI) parameters for several neighboring shells are determined. It is found that the relevant parameters for the two studied matrices differ, in spite of the fact that the nearest environment of the rare earth ion is nearly identical. A first-principles theoretical analysis is performed for the THFI parameters of the first coordination shell of F- ions. Several mechanisms of metal ion-ligand coupling are considered and it is found that one of them, ligand polarization, explains the difference observed for the THFI parameters in Cs2 NaY F6 and CsCa F3. © 2009 The American Physical Society.

SrF2 and BaF2 crystals, doped with the Yb3+ ions, have been investigated by electron paramagnetic resonance and optical spectroscopy. As-grown crystals of SrF2 and BaF2 show the two paramagnetic centres for the cubic (Tc) and trigonal (T4) symmetries of the Yb3+ ions. Empirical diagrams of the energy levels were established and the potentials of the crystal field were determined. Information was obtained on the SrF2 and BaF2 phonon spectra from the electron-vibrational structure of the optical spectra. The crystal field parameters were used to analyse the crystal lattice distortions in the vicinity of the impurity ion and the F- ion compensating for the excess positive charge in T4. Within the frames of a superposition model, it is shown that three F- ions from the nearest surrounding cube, located symmetrically with respect to the C3 axis from the side of the ion-compensator, approach the impurity ion and cling to the axis of the centre when forming T4. The F- ion located on the axis of the centre between the Yb3+ ion and ion-compensator, also approaches close to the impurity ion.

A trigonal Yb3+ paramagnetic center in the CsCaF3 single crystal was studied by magnetic resonance and optical spectroscopy methods. The structural model of the complex and the empirical energy level scheme were established. The transferred hyperfine interaction parameters and the crystal field ones were determined. The crystal field parameters were used to analyze the lattice distortions in the vicinity of Yb3+ using the superposition model. © 2010 Springer-Verlag.