THE OPTICAL PROPERTIES OF Pr3+ EMBEDDED IN THE RARE EARTH BOROGERMANATE MATRICES: REBGeO5

The luminescent properties of the trivalent praseodymium ion in the trigonal borogermanate matrice PrBGeO5 have been analysed. The energy level schemes are deduced from the absorption and emission spectra and reproduced with 14 crystal field parameters (cfps) according to the local point symmetry occupied by the rare earth element in the matrix.The luminescent properties of the trivalent praseodymium ion in the trigonal borogermanate matrice PrBGeO5 have been analysed. The energy level schemes are deduced from the absorption and emission spectra and reproduced with 14 crystal field parameters (cfps) according to the local point symmetry occupied by the rare earth element in the matrix

High resolution infrared absorption spectra, crystal field, and relaxation processes in CsCdBr_3:Pr^3+

High resolution low-temperature absorption spectra of 0.2% Pr^3+ doped CsCdBr_3 were measured in the spectral region 2000--7000 cm-1. Positions and widths of the crystal field levels within the 3H5, 3H4, 3F2, and 3F3 multiplets of the Pr^3+ main center have been determined. Hyperfine structure of several spectral lines has been found. Crystal field calculations were carried out in the framework of the semiphenomenological exchange charge model (ECM). Parameters of the ECM were determined by fitting to the measured total splittings of the 3H4 and 3H6 multiplets and to the observed in this work hyperfine splittings of the crystal field levels. One- and two-phonon relaxation rates were calculated using the phonon Green's functions of the perfect (CsCdBr_3) and locally perturbed (impurity dimer centers in CsCdBr_3:Pr^3+) crystal lattice. Comparison with the measured linewidths confirmed an essential redistribution of the phonon density of states in CsCdBr_3 crystals doped with rare-earth ions.Comment: 16 pages, 5 tables, 3 figure

Crystal field and magnetic ordering in the Haldane-chain compound Er 2BaNiO5 as studied by optical spectroscopy

High-resolution absorption spectra of the chain compound Er 2BaNiO5 were measured in a wide range of frequencies (6000-20,000 cm-1) and temperatures (2.5-300 K). Energies of 38 crystal-field levels of Er3+ in a paramagnetic Er 2BaNiO5 were determined. Exchange splittings of crystal-field levels in the antiferromagnetically ordered state (TN = 34 K) were measured. Crystal-field calculations were performed and the obtained wave functions were used to calculate the temperature dependence of the magnetic susceptibility to be compared with the detailed experimental dependence measured in this work. © 2004 Elsevier B.V. All rights reserved

High-resolution spectral study of Er3+ crystal-field levels and magnetic ordering in (ErxY1-x)2BaNiO 5 chain compounds

A family of linear chain nickelates (ErxY1-x) 2BaNiO5 (x = 1, 0.8, 0.6, 0.4, 0.2, and 0.1) was studied by high-resolution spectroscopy of the Er3+ ion. Energies of 38 crystal-field levels of Er3+ and exchange splittings for most of them in a magnetically ordered state were measured. Composition-dependent Néel temperatures were found. Crystal-field calculations were performed starting from the analysis in the framework of the exchange-charge model. The wave functions found were used to calculate magnetic g factors for crystal-field levels of Er3+ and the magnetic susceptibility χ(T) of the concentrared x = 1 compound. The latter was compared to the detailed χ(T) curve (2.0 K<T<300 K) measured for the Er2BaNiO 5 powdered sample. From the experimentally measured temperature dependences for the ground-state splittings in the compounds with different composition, we derive, within the molecular-field approximation, the ordered magnetic moments of the nickel and erbium subsystems as functions of temperature and concentration of erbium ions, and plot the staggered magnetization function of nickel chains for a staggered magnetic field along the chain direction

Optical spectra, crystal-field parameters, and magnetic susceptibility of the new multiferroic NdFe3(BO3)4

We report high-resolution optical absorption spectra for NdFe3(BO3)4 trigonal single crystal which is known to exhibit a giant magnetoelectric effect below the temperature of magnetic ordering TN = 33 K. The analysis of the temperature-dependent polarized spectra reveals the energies and, in some cases, symmetries and exchange splittings of Nd3+ 84 Kramers doublets. We perform crystal-field calculations starting from the exchange-charge model, obtain a set of six real crystal-field parameters, and calculate wave functions and magnetic g-factors. In particular, the values g(perpendicular) = 2.385, g(parallel) = 1.376 were found for the Nd3+ ground-state doublet. We obtain Bloc=7.88 T and |JFN|= 0.48 K for the values of the local effective magnetic field at liquid helium temperatures at the Nd3+ site and the Nd - Fe exchange integral, respectively, using the experimentally measured Nd3+ ground-state splitting of 8.8 cm-1. To check reliability of our set of crystal field parameters we model the magnetic susceptibility data from literature. A dimer containing two nearest-neighbor iron ions in the spiral chain is considered to partly account for quasi-one-dimensional properties of iron borates, and then the mean-field approximation is used. The results of calculations with the exchange parameters for Fe3+ ions Jnn = -6.25 K (intra-chain interactions) and Jnnn = -1.92 K (inter-chain interactions) obtained from fitting agree well with the experimental data.Comment: 13 pages, 8 figures, 2 table

High-resolution optical spectroscopy investigation of Nd 2BaNiO 5 and Nd 0.1Y 1.9BaNiO 5 and crystal-field parameters for rare-earth linear-chain nickelates

High-resolution spectroscopy of Nd 3+ in Nd 2BaNiO 5 and Y 2BaNiO 5:Nd(5%) powder samples is used to study Nd 3+ crystal-field levels and exchange splittings in these quasi-one-dimensional model compounds. We demonstrate that the Nd 3+ ground-state splitting in the magnetically ordered state of Nd 2BaNiO 5 (T N = 47.5 ± 1 K, as found from our spectroscopic data) accounts for the low-temperature magnetic properties and for the 4-meV mode observed earlier in inelastic neutron scattering experiments. Crystal-field analysis is performed. Its results show that the directions of ordered magnetic moments in Nd 2BaNiO 5 are determined by the single-ion anisotropy of Nd 3+. We argue that the crystal-field parameters obtained for Nd-nickelate (in this work) and Er-nickelate (in our earlier work) can be used to predict the energy-level patterns and magnetic orooerties of other rare-earth linear-chain nickelates. ©2005 The American Physical Society

Optical spectra, crystal-field parameters, and magnetic susceptibility of multiferroic Nd Fe3 (B O3) 4

We report high-resolution optical absorption spectra for Nd Fe3 (B O3) 4 trigonal single crystal, which is known to exhibit a giant magnetoelectric effect below the temperature of magnetic ordering TN =33 K. The analysis of the temperature-dependent polarized spectra reveals the energies and, in some cases, symmetries and exchange splittings of Nd3+ 84 Kramers doublets. We perform crystal-field calculations starting from the exchange-charge model, obtain a set of six real crystal-field parameters, and calculate wave functions and magnetic g factors. In particular, the values g =2.385 and g =1.376 were found for the Nd3+ ground-state doublet. We obtain Bloc =7.88 T and JFN =0.48 K for the values of the local effective magnetic field at liquid-helium temperatures at the Nd3+ site and the Nd-Fe exchange integral, respectively, using the experimentally measured Nd3+ ground-state splitting of 8.8 cm-1. To check the reliability of our set of crystal-field parameters, we model the magnetic susceptibility data from literature. A dimer containing two nearest-neighbor iron ions in the spiral chain is considered to partly account for quasi-one-dimensional properties of iron borates, and then the mean-field approximation is used. The results of calculations with the exchange parameters for Fe3+ ions Jnn =-6.25 K (intrachain interactions) and Jnnn =-1.92 K (interchain interactions) obtained from fitting agree well with the experimental data. © 2007 The American Physical Society

Optical spectroscopy of Yb2Ti2O7 and Y2Ti2O7: Yb3+ and crystal-field parameters in rare-earth titanate pyrochlores

Optical absorption spectra of the Yb2Ti2O7 single crystals and luminescence spectra of the Y2Ti 2O7:Yb (1%) polycrystalline samples were registered at temperatures 4.2-300 K. These spectra and earlier published data on magnetic properties of Yb3+ ions and on the temperature dependence of the electric field gradient at Yb nuclei in Yb2Ti2O 7 were used to analyze the crystal-field parameters in rare-earth titanates with the pyrochlore structure. The self-consistent sets of crystal-field parameters for rare-earth ions in the 16d sites with the D 3d symmetry that describe satisfactory all known single-ion magnetic properties and low-energy excitations in R2Ti2O 7 crystals (R=Tb, Ho, Er, Tm, Yb) are presented

Stark structure of the Yb3+ ion levels in (YbxY 1-x)2Ti2O7 and the crystal field in rare-earth titanates with a pyrochlore structure

The absorption spectra of Yb2Ti2O7 single crystals and the luminescence and luminescence excitation spectra of Y 2Ti2O7: Yb (1%) polycrystals were studied in the temperature range 4.2-300 K. The spectra were analyzed in terms of the crystal-field theory and the exchange-charge model. Based on the set of crystal-field parameters found for Yb2Ti2O7, analogous sets of parameters were determined for other rare-earth titanates and proved to be in reasonable agreement with all available experimental data. © 2005 Pleiades Publishing, Inc

Experimental and theoretical study of α–Eu2(MoO4)3 under compression

The compression process in the α-phase of europium trimolybdate was revised employing several experimental techniques. X-ray diffraction (using synchrotron and laboratory radiation sources), Raman scattering and photoluminescence experiments were performed up to a maximum pressure of 21 GPa. In addition, the crystal structure and Raman mode frequencies have been studied by means of first-principles density functional based methods. Results suggest that the compression process of α-Eu2(MoO4)3 can be described by three stages. Below 8 GPa, the α-phase suffers an isotropic contraction of the crystal structure. Between 8 and 12 GPa, the compound undergoes an anisotropic compression due to distortion and rotation of the MoO4 tetrahedra. At pressures above 12 GPa, the amorphization process starts without any previous occurrence of a crystalline-crystalline phase transition in the whole range of pressure. This behavior clearly differs from the process of compression and amorphization in trimolybdates with β′-phase and tritungstates with α-phase.We thank Diamond Light Source for access to beamline I15 (EE1746) that contributed to the results presented here. Part of the diffraction measurements were performed at the 'Servicio Integrado de Difraccion de Rayos X (SIDIX)' of University of La Laguna. This work has been supported by Ministerio de Economia y Competitividad of Spain (MINECO) for the research projects through the National Program of Materials (MAT2010-21270-C04-01/02/03/04, MAT2013-46649-C41/2/3/4-P and MAT2013-43319-P), the Consolider-Ingenio 2010 MALTA (CSD2007-00045), the project of Generalitat Valenciana (GVA-ACOMP/2014/243) and by the European Union FEDER funds. C Guzman-Afonso wishes to thank ACIISI and FSE for a fellowship. J A Sans thanks the FPI and 'Juan de la Cierva' programs for fellowships.Guzmán-Afonso, C.; León-Luis, S.; Sans-Tresserras, JÁ.; González -Silgo, C.; Rodríguez-Hernández, P.; Radescu, S.;  muñoz, A.... (2015). Experimental and theoretical study of α–Eu2(MoO4)3 under compression. Journal of Physics: Condensed Matter. 27(46):465401-1-465401-11. https://doi.org/10.1088/0953-8984/27/46/465401S465401-1465401-11274