Luminescence properties of Y2O3:Bi3+, Ln3+ (Ln=Sm,Eu, Dy,Er, Ho) and the sensitization of Ln3+ by Bi3+

The spectroscopic characterization of yttria, singly and doubly doped with Ln³⁺ (Ln=Sm, Eu, Dy, Er, Ho) and Bi³⁺ ions, is performed through excitation spectra, emission spectra and decay time measurements. The obtained spectroscopic data clearly indicate that energy transfer takes place from Bi³⁺ to Ln³⁺ ions. The energy transfer efficiency of Bi³⁺→Ln³⁺ and quantum efficiency of Ln³⁺ were calculated. Upon excitation of 370 nm (Bi³⁺ excitation band), the quantum efficiency of Ln³⁺ varies from ～4% to ～44%. The energy transfer efficiency increases continuously with increasing Ln³⁺ concentrations, whereas the variation of the quantum efficiency of Ln³⁺ is complicated. The quantum efficiency of Ln³⁺ is discussed in terms of electron transfer and cross relaxation.     

Positron annihilation studies in high-Tc superconductors RBa2Cu3Oy,R: La,Nd, Sm,Eu, Gd,Dy, Ho,Y, Er

Positron lifetime and Doppler broadening of the annihilation line measurements have been performed at room temperature in high-T_c superconductors RBa₂Cu₃O_y, where R: La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er and 6.9 < y ≤ 7. Doppler broadening of the annihilation line measurements have also been performed in high-T_c superconducting samples R RBa₂Cu₃O_y, where R: Nd, Sm, Eu, Ho, Y, Er as a function of temperature between 14 K and 293 K. It was observed that the positron lifetime and the S parameter values at room temperature have no obvious trend in their variation from the yttrium substitution by a rare-earth element. It was also observed that the temperature dependence of the positron annihilation parameters is similar in the high-T_c superconducting samples.     

Magnetic properties of R2Pt compounds with R = Gd,Tb, Dy,Ho, Er and Tm

Magnetic properties of polycrystalline samples of R₂Pt compounds (R = Gd, Tb, Dy, Ho, Er and Tm) are presented. The Gd, Td, Dy, Ho based compounds are ferromagnetic with Curie temperatures ranging between 155 and 17 K. Er₂Pt and Tm₂Pt are antiferromagnetic with Néel temperatures of 9 and 5 K respectively. The observed properties are discussed considering indirect exchange interactions and crystal field effects acting on the rare earth ions which lies in very low symmetry sites.     

Photoluminescence investigations of Li2SiO3:Ln (Ln=Er3+, Eu3+, Dy3+, Sm3+) phosphors

In this study, we report a comprehensive structural and photoluminescence (PL) study on lithium metasilicate (Li₂SiO₃) phosphor ceramics doped with four rare earth (RE) ions. X-ray diffraction (XRD) patterns show a dominant phase, characteristic of the orthorhombic structure Li₂SiO₃ compound and the presence of dopants has no effect on the basic crystal structure of the material. The first excited state Er³⁺ luminescence at 1.54 μm arises from a sharp atomic-like radiative transition between the ⁴I_13/2 state and the ⁴I_15/2 state (ground level) under a 532 nm line of an Ar ion laser excitation. Sm doped samples showed Sm³⁺ emission characteristics corresponding to the some ⁴G_5/2→⁶H_j (j=5/2,9/2,11/2) transitions indicating a strong crystal-field effect. PL spectra of Eu doped material exhibited peaks corresponding to the ⁵D₀→⁷F_j (j=0,1,2,3 and 4) transitions under 405 nm excitation. The dominant red color emission at 612 nm from the hypersensitive (⁵D₀→⁷F₂) transition of Eu³⁺ indicates the inversion antisymmetry crystal field around Eu³⁺ ion, which is favorable to improve the red color purity. Dy doped samples showed the Dy³⁺ emission characteristic due to the ⁴F_9/2→⁶H_13/2 transition. Their relative intensity ratios also suggested the presence of a symmetric environment around the metal ion. We suggest that lithium metasilicate has enough potential candidates to be a phosphor material.     

Magnetic properties of R2WO6 (where R=Nd, Sm, Eu, Gd, Dy and Ho)

The magnetic and electrical measurements carried out on the R₂WO₆ tungstates showed a paramagnetic behaviour for samples with R=Nd, Gd, Dy and Ho and more complex one for samples with R=Sm and Eu in the temperature range 4.2-280 K and an insulating state at room temperature. With increasing atomic number of the R element the Curie-Weiss temperature increases from −43.5 K for Nd₂WO₆ to −2.7 K for Ho₂WO₆, excluding Sm₂WO₆ and Eu₂WO₆ compounds for that the Curie-Weiss region is not observed and the imaginary part of susceptibility is close to zero. The effective magnetic moment is close to the theoretical one for the free R ion and the magnetic moment measured in magnetic field of 14 T and at temperature of 4.2 K, generally, does not reach the saturation state. The temperature independent residual susceptibility is negative for Nd₂WO₆ and positive for the remaining compounds suggesting different proportions of the Landau, Pauli and van Vleck contributions to the total susceptibility. An increase of the orbital magnetic contribution to the total magnetic moment is suggested from the fitting of the Landé factor in the compounds under study.     

Magnetic properties of RE2Au compounds (RE = Pr,Nd, Gd,Tb, Dy,Ho, Er,Tm and Y)

Magnetic properties of nine RE₂Au compounds have been studied in fields of up to 19 kOe in the temperature range 4.2K–300K. It has been found that all compounds are paramagnetic at room temperature except Gd₂Au. The compounds with Pr, Nd, Ho, Er and Tm exhibit Curie-Weiss behaviour with paramagnetic moments in close agreement with those expected for the free RE³⁺ ion. The moment of gold was found to be zero. The compounds with Pr, Nd, Tb, Dy, Er and Tm are antiferromagnetic at low temperatures. It appears that Ho₂Au is ferromagnetically ordered below 4.5 K. No evidence for magnetic ordering was found for Y₂Au. The compound with Tb exhibits metamagnetic behaviour.     

Synthesis and magnetic properties of ternary carbides R2Fe14C (R = Pr,Sm, Gd,Tb, Dy,Ho, Er,Tm, Lu) with Nd2Fe14B structure type

The R₂Fe₁₄C compounds were prepared from the elements by arc melting and long-time annealing (more than 480 hrs) at temperatures below 1200 K. They crystallize with the tetragonal Nd₂Fe₁₄B structure type as shown by X-ray powder diffraction analysis. All samples contain at least 70 vol.% of the R₂Fe₁₄C phase. Both saturation magnetization values (42–133 Am²/kg) and Curie temperatures (493–613 K) are lower than those measured on the corresponding borides.     

A crystal field investigation of the properties of RCuAs2 (R=Pr, Nd, Sm, Tb, Dy, Ho, Er and Yb)

A crystal field (CF) investigation of the magnetic properties and heat capacities of RCuAs₂ (R=Pr, Nd, Sm, Tb, Dy, Ho, Er and Yb) has been carried out using the observed average magnetic susceptibilities (1.8-300 K) of the title compounds. The CF parameters proposed for the systems show a systematic variation throughout the rare-earth series. Other physical properties dependent on the CF are also computed and compared with available experimental data. The experimental heat capacity data reported for a limited range of temperature agree well with computed heat capacity for all the compounds (except SmCuAs₂ and YbCuAs₂). CF J mixing was found to be appreciable for all the samples except YbCuAs₂.     

Anomalous hyperfine field and orbital moment of cobalt in RCo2; R = Pr,Nd, Sm,Gd, Tb,Dy, Ho,Er and Tm

⁵⁹Co spin echo NMR spectra in the magnetically ordered phase of the MgCu₂ type RCo₂ compounds (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm) have been observed. For the RCo₂ with the easy direction of magnetication parallel to the 〈011〉 or 〈111〉 direction, the ⁵⁹Co hyperfine fields at two magnetically inequivalent Co sites are found to be antiparallel, revealing a large anisotropy in the ⁵⁹Co hyperfine field. The results are discussed in terms of a large and anisotropic orbital moment of Co. The transferred hyperfine field due to rare earth spins is estimated from well resolved satellite lines observed in Tb_1?xY_xCo₂. The nuclear quadrupole splitting in the magnetically ordered phase is found to be always larger than that in the paramagnetic phase.     

Magnetismus in den intermetallischen SEAu3-Verbindungen (SE=Gd,Tb, Dy,Ho, Er und Tm)

The relation between inner displacement and strain is established and simplified by group theory. Results are given for the diamond structure (C, Ge, Si), cobalt (Co), graphite (C), neodymium (Nd), spinel (MgAl₂O₄). For these crystals we get an enormous reduction of the number of parameters to be determined by measurement.     

Luminescence and Nonlinear Optical Properties of Borates LnGa3(BO3)4 (Ln = Nd,Sm, Tb,Er, Dy,or Ho)

Optics and Spectroscopy - Luminescence spectra of single crystals of rare-earth gallium borates LnGa3(BO3)4 (Ln = Nd, Sm, Tb, Er, Dy, or Ho) at room (300 K) and cryogenic (10&nbsp;K)...     

Structural relative stabilities and pressure-induced phase transitions for lanthanide trihydrides REH3 (RE=Sm,Gd, Tb,Dy, Ho,Er, Tm,and Lu)

The structures, structural relative stabilities, pressure-induced phase transitions, and equations of state for lanthanide trihydrides REH₃ (RE=Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) are systematically studied using ab initio calculations under a core state model (CSM). The obtained ground-state parameters, such as lattice constants and bulk modulus, agree well with the available data. Among the P6₃/mm, P3?c1, and P6₃cm structures, the P6₃cm structure is found to be the most stable structure for lanthanide trihydride via the comparison of the calculated total energies. With the help of Birch–Murnaghan equation of state, the structural transitions from hexagonal to cubic for REH₃ (RE=Sm, Gd, Ho, Er, and Lu) under pressure are affirmed; especially, the similar behavior of REH₃ (RE= Tb, Dy, and Tm) is reasonably predicted for the first time by this means. For the transitions, the repulsive interactions of H–H atoms may play an important role in terms of the analysis of the structures in the vicinity of the theoretical phase transition.     

Magnetic properties of the compounds R2Sc3Si4 (R=Gd, Tb, Dy, Ho, Er)

The magnetization of R₂Sc₃Si₄ compounds is measured in static magnetic fields up to 14 kOe in the temperature range 77–300 K. It is established that all compounds in the given series are paramagnetic at these temperatures. The paramagnetic Curie points are determined, and the effective magnetic moments are calculated. The measurements are performed on polycrystalline samples. Fiz. Tverd. Tela (St. Petersburg) 41, 1804–1805 (October 1999)