Lanthanide Cations Research Articles

Taming Super-Reduced Bi23- Radicals with Rare Earth Cations.

Here, we report the synthesis of two new sets of dibismuth-bridged rare earth molecules. The first series contains a bridging diamagnetic Bi22- anion, (Cp*2RE)2(μ-η2:η2-Bi2), 1-RE (where Cp* = pentamethylcyclopentadienyl; RE = Gd (1-Gd), Tb (1-Tb), Dy (1-Dy), Y (1-Y)), while the second series comprises the first Bi23- radical-containing complexes for any d- or f-block metal ions, [K(crypt-222)][(Cp*2RE)2(μ-η2:η2-Bi2•)]·2THF (2-RE, RE = Gd (2-Gd), Tb (2-Tb), Dy (2-Dy), Y (2-Y); crypt-222 = 2.2.2-cryptand), which were obtained from one-electron reduction of 1-RE with KC8. The Bi23- radical-bridged terbium and dysprosium congeners, 2-Tb and 2-Dy, are single-molecule magnets with magnetic hysteresis. We investigate the nature of the unprecedented lanthanide-bismuth and bismuth-bismuth bonding and their roles in magnetic communication between paramagnetic metal centers, through single-crystal X-ray diffraction, ultraviolet-visible/near-infrared (UV-vis/NIR) spectroscopy, SQUID magnetometry, DFT and multiconfigurational ab initio calculations. We find a πz* ground SOMO for Bi23-, which has isotropic spin-spin exchange coupling with neighboring metal ions of ca. -20 cm-1; however, the exchange coupling is strongly augmented by orbitally dependent terms in the anisotropic cases of 2-Tb and 2-Dy. As the first examples of p-block radicals beneath the second row bridging any metal ions, these studies have important ramifications for single-molecule magnetism, main group element, rare earth metal, and coordination chemistry at large.

Growth of Sesquioxide Crystals from Tungsten Crucibles by Vertical Gradient Freezing Method

Sesquioxides of lanthanides, yttrium, and scandium are promising hosts for laser and scintillation materials; however, the crystallization of such compounds is complicated by very high melting temperatures, as well as polymorph transitions. This work reports for the first time the growth of Y2O3 and Y2−xScxO3 crystals by the Vertical Gradient Freezing method from tungsten crucibles, proposing an alternative to extremely expensive rhenium and iridium crucibles. Translucent Y2O3 samples are obtained, and their luminescent and scintillation parameters are evaluated. The main issues of Y2O3 crystallization under the proposed conditions are discussed, as well as ways of enhancing the crystal quality. Finally, polymorph transitions are avoided by decreasing the average radius of the rare earth cation by Y3+/Sc3+ substitution, providing transparent Y2−xScxO3 crystals with a cubic structure.

Solvent extraction in non-ideal eutectic solvents – Application towards lanthanide separation

Hydrophobic eutectic solvents (HES) emerged as promising substitutes to the conventional organic phase used in the solvent extraction (SX) of metal ions due to the avoidance of diluents and the suppression of third-phase manifestation. However, HES present a highly structured liquid phase defined by hydrogen-bonded interactions such that intercomponent interactions are expected to play a greater role in SX using HES compared to a diluted extractant solution. In this work, the extraction of lanthanides from nitrate media by the non-ideal solvent composed of decanoic acid (C10OOH) and trioctylphosphine oxide (TOPO) was determined as a function of the lanthanide cation selection, HES molar fraction, HNO3 concentration, and temperature. Through the systematic variation of these parameters, the delicate balance between complexation and solvent reorganisation and its influence on the extraction and metal selectivity is determined by metal partition experiments, time resolved fluorescence and Raman spectroscopy, and small-angle X-ray scattering (SAXS). A compromise between maximum Ln3+ loading and selectivity was observed, driven by the variation in the quantity of weakly H-bonded TOPO and the change in the configurational entropy of the mixture. All results point towards the need to explicitly consider the HES phase structuration and its compositional changes with solute co-extraction on the Ln3+ extraction as no change in the extracted complex speciation was observed across all tested conditions. The C10OOH + TOPO was used as a model system due as lanthanide extraction using TOPO and carboxylic extractants is well described whilst the phase diagram and properties of the eutectic are reported. Nevertheless, the derived conclusions are translatable to other systems and can help guide the design and application of possible HES combinations for SX.

Stability of the Structural and Transport Characteristics of (ZrO2)0.99−x(Sc2O3)x(R2O3)0.01 (R–Yb, Y, Tb, Gd) Electrolytic Membranes to High-Temperature Exposure

The effect of long-term high-temperature annealing on the phase composition, local crystal structure, and oxygen-ion conductivity of SOFC membranes based on zirconium dioxide solid solutions was studied. Crystals with the composition of (ZrO2)0.99-x(Sc2O3)x(R2O3)0.01 (where x = 0.08-0.1; R-Yb, Y, Tb, Gd) were obtained by the method of directed melt crystallization in a cold crucible. The crystals were annealed in air at a temperature of 1000 °C for 400 h. The phase analysis of the crystals before and after annealing was studied by X-ray diffractometry and Raman spectroscopy. The study of the ionic conductivity of the crystals was carried out by the method of impedance spectroscopy in the temperature range 400-900 °C. It has been shown that when various rare earth cations (Yb, Y, Tb, and Gd) are used, the maximum conductivity is observed for the compositions (ZrO2)0.91(Sc2O3)0.08(Yb2O3)0.01, (ZrO2)0.89(Sc2O3)0.1(Y2O3)0.01, (ZrO2)0.90(Sc2O3)0.09(Tb2O3)0.01, and (ZrO2)0.89(Sc2O3)0.1(Gd2O3)0.01. At the same time, these crystals have a highly symmetrical pseudocubic structure, which is retained even after crystal annealing. At comparable concentrations of Sc2O3, the conductivity of crystals decreases with an increase in the ionic radius of the rare earth cation. The high-temperature degradation of the conductivity is also discussed depending on the type of rare earth oxide and the concentration of scandium oxide.

Manipulation of ferroelectric polarization and light absorption in non-noble metal/Aurivillius ferroelectric hybrid to enhance self-driven photodetection by coupling ferro-pyro-phototronic and plasmonic effect

Aurivillius ferroelectrics materials with layer perovskite structure, spontaneous polarization and ferro-pyro-phototronic effect afford a promising avenue for self-powered photodetectors. Nevertheless, poor photo-response caused by weak remanent polarization and low absorption coefficient hinders their further application. Herein, we demonstrate an excellent self-powered photodetector in nanosheets-assembled Bi microspheres array/Nd-doped Bi4Ti3O12 [Bi3.8Nd0.2Ti3O12] nanofibers heterostructured, which can rationally couple between ferroelectric polarization and ferro-pyro-phototronic effect in Aurivillius ferroelectric Bi3.8Nd0.2Ti3O12 and plasmonic effect in non-noble metal Bi. Firstly, an A-site doping with lanthanoid cation Nd3+ and dimension lowering strategy is proposed to improve the ferroelectric properties by reducing the oxygen vacancy concentration and coercive force field of Bi4Ti3O12 nanofibers through electrospinning method. Furthermore, the Bi nanosheets-assembled microspheres array allowing multiple reflection and scattering of incident light is introduced to enhance the local electromagnetic field and light absorption of Bi3.8Nd0.2Ti3O12. Ultimately, the Bi@Bi3.8Nd0.2Ti3O12 with negatively polarized obtains a superior zero-bias photocurrent of -500 nA under 390 nm laser illumination, which is 195.31 and 22.16 times higher than unpolarized Bi4Ti3O12 and Bi3.8Nd0.2Ti3O12, respectively. Simultaneously, an outstanding detectivity (8.11 ×1011 Jones) and fast photoresponse time (57/114 µs) are correspondingly achieved. Our research provides a reliable way to simultaneously realize large ferroelectric polarization and high light absorption for jointly manipulation of electrons and photons in self-powered optoelectronic devices.

Design rules for the thermal and elastic properties of rare-earth disilicates

Rare-earth silicates are the current standard material for use as environmental barrier coatings for SiC-based ceramic matrix composites as hot-section components in gas-turbine engines. Expanding the design space to all available rare-earth elements to facilitate optimizing functionality requires an understanding of systematic trends in RE2Si2O7 properties. In this work, we combine first-principles calculations with experimental measurements of Young’s modulus, coefficient of thermal expansion, and thermal conductivity for a range of different RE2Si2O7 compositions and phases. Clear trends are observed in these properties as a function of the radius of the rare-earth cation. In the case of Young’s modulus and thermal expansion, these trends also hold for multi-component systems; while the thermal conductivity of multi-component systems is noticeably lower, indicating the potential of such materials to also act as thermal barriers. These results provide design rules for developing new thermal and environmental barrier coatings with stiffness and thermal expansion engineered to match that of the substrate, while simultaneously having reduced thermal conductivity.

Doping rare earth cations with an additional chemical reduction synergistically weakened the photocatalytic performance of ceria.

Chemical reducing or rare earth cations (RE) doping was normally employed to promote the photocatalytic performance of ceria, aimed to evaluate their cooperation influences, ceria was obtained by decomposing homogenously RE (RE = La, Sm, and Y)-doped CeCO3OH in H2. XPS and EPR results evidenced that the excess oxygen vacancies (OVs) were formed in RE-doped CeO2 compared to the un-doped ceria. However, all the RE-doped ceria unexpectedly showed an impeded photocatalytic activity towards to methylene blue (MB) photodegradation. The 5% Sm-doped ceria had the best MB photodegradation ratio of 81.47% after 2-h reaction in all RE-doped samples, which was lower than that of 87.24% for the un-doped ceria. After doping RE cations and chemical reducing, the band gap of ceria were almost narrowed, while the PL spectra and photo-electro characterizations indicated that the separation efficiency of photo-excited e-/h+ (electrons/holes) was reduced. The RE dopants and formed excess OVs including inner and surface OVs was proposed to promote the recombination of e-/h+ which further hindered the generation of active species of ·O2- and ·OH, and finally weakened the photocatalytic activity of ceria.

Chelator-Free Radiolabeling with Theoretical Insights and Preclinical Evaluation of Citrate-Functionalized Hydroxyapatite Nanospheres for Potential Use as Radionanomedicine

Biomimetic hydroxyapatite nanoparticles (HAnps) are among the few nanostructured materials used clinically as potential carriers of drugs and biomolecules. Moreover, they have strong affinity toward lanthanide cations (such as Sm+3, Lu+3, Ho+3, etc.), which provides the scope for robust chelator-free radiolabeling with suitable lanthanide radioisotopes. Therefore, this nanoplatform can be used as a carrier of a cytotoxic payload of therapeutic radioisotopes. In the present study, HAnps were synthesized by the sol–gel method and functionalized with sodium citrate to impart water dispersibility. The synthesized nanoparticles were characterized using various analytical techniques. The particle size of the citrate-functionalized hydroxyapatite nanoparticles (Cit-HAnps) was found to be 205 ± 7 nm. A chelator-free method to radiolabel the Cit-HAnp with 177Lu [T1/2 = 6.65 days, Eβ(max) = 497 keV, Eγ = 113 (6.4%) and 208 keV (11.0%)] was optimized to get the 177Lu-labeled nanoformulation with >98% radiochemical purity. The adsorption-based radiolabeling method followed the Langmuir isotherm and pseudo-second-order kinetic model, indicating that the process was chemisorption. In vitro bone binding and cell toxicity study established the therapeutic efficacy of the radiolabeled nanoparticles. SPECT/CT imaging in healthy Wistar rats after administration of the radiolabeled nanoparticles was performed to demonstrate the in vivo stability and clearance pattern. Density functional theory (DFT) calculations were performed to provide the structural modification of Cit-HAnps and a glimpse into the probable mechanism of chelator-free labeling of 177Lu on Cit-HAnps. Overall, this class of nanomaterials provides an avenue toward the development of clinically translatable radionanomedicine for use in cancer theranostics.

Synthesis, Crystal Structure and Properties of the New Laminar Quaternary Tellurides SrLnCuTe3 (Ln = Sm, Gd–Tm and Lu)

This paper reports for the first time on the new laminar quaternary orthorhombic heterometallic quaternary tellurides SrLnCuTe3, the fabrication of which has been a challenge until this work. Data on the crystal structure of tellurides complete the series of quaternary strontium chalcogenides SrLnCuCh3 (Ch = S, Se, Te). Single crystals of the compounds were synthesized from the elements by the halogenide-flux method at 1070 K. The compounds are crystallizing in two space groups Pnma (Ln = Sm, Gd and Tb) and Cmcm (Ln = Dy–Tm and Lu). For SrSmCuTe3 (a = 11.4592(7), b = 4.3706(3), c = 14.4425(9) Å, space group: Pnma) with the largest lanthanoid cation, Sr2+ shows C.N. = 7, whereas Sm3+ reveals a diminished coordination number C.N. = 6. For SrLuCuTe3 (a = 4.3064(3), b = 14.3879(9), c = 11.1408(7) Å, space group: Cmcm) with the smallest lanthanoid cation, coordination numbers of six are realized for both high-charged cations (Sr2+ and Lu3+: C.N. = 6). The cations Sr2+, Ln3+, Cu+ each take independent positions. The structures are built by distorted [CuTe4]7– tetrahedra, forming the infinite chains {∞1[Cu(Te1)1/1t(Te2)1/1t(Te3)2/2e]5−} along [010] in SrLnCuTe3 (Ln = Sm, Gd and Tb) and [100] in SrLnCuTe3 (Ln = Dy–Tm and Lu). The distortion of the polyhedra [CuTe4]7– was compared for the whole series SrLnCuTe3 by means of τ4-descriptor for the four coordinating Te2– anions, which revealed a decrease in the degree of distortion with a decreasing radius at Ln3+. The distorted octahedra [LnTe6]9– form layers {∞2[Ln(Te1)2/2(Te2)2/2(Te3)2/2]3−}. The distorted octahedra and tetrahedra fuse to form parallel layers {∞2[CuLnTe3]2−} and between them, the Sr2+ cations providing three-dimensionality of the structure are located. In the SrLnCuTe3 (Ln = Sm, Gd and Tb) structures, the Sr2+ cations center capped the trigonal prisms [SrTe6+1]12−, united in infinite chains {∞1[Sr(Te1)2/2(Te2)3/3(Te3)2/2]4−} along the [100] direction. The domains of existence of the Ba2MnS3, BaLaCuS3, Eu2CuS3 and KZrCuS3 structure types are defined in the series of orthorhombic chalcogenides SrLnCuCh3 (Ch = S, Se and Te). The tellurides SrLnCuTe3 (Ln = Tb–Er) of both structure types in the temperature range from 2 up to 300 K are paramagnetic, without showing clear signs of a magnetic phase transition.

Mechanical property enhancements and amorphous thermal transports of ordered weberite-type RE3Nb/TaO7high-entropy oxides

A₃BO₇-type (A = rare earth (RE), B = Nb or Ta) oxides have been studied as protective coating materials because of their low thermal conductivity; however, their hardness, toughness, and stiffness are insufficient, particularly for members with webeirte-type structures. In this work, we have synthesized two high-entropy oxides (HEOs) of weberite-type RE niobates/tantalates (RE₃Nb/TaO₇), i.e., (Nd_1/7Sm_1/7Eu_1/7Gd_1/7Dy_1/7Ho_1/7Er_1/7)₃NbO₇ (7HEOs-Nb) and (Nd_1/7Sm_1/7Eu_1/7Gd_1/7Dy_1/7Ho_1/7Er_1/7)₃(Nb_1/2Ta_1/2)O₇ (7HEOs-NbTa), to overcome the mechanical deficiencies. The short- and long-range ordered arrangements of RE cations in the A-site and Nb/Ta cations in the B-site were identified by the X-ray diffraction (XRD), scanning electron microscopy equipped with energy-dispersive spectrometry (EDS), and transmission electron microscopy. The enhancements in hardness (<i>H</i> = 9.4 GPa) and fracture toughness (<i>K</i>_IC = 2.0 MPa·m^1/2) were realized by grain refinement, solid solution strengthening, and high stiffness (<i>K</i>). The exceptional phase stability at 25−1500 ℃, amorphous thermal conductivity (<i>k</i> = 1.5−1.7 W·m⁻¹·K⁻¹ at 25−900 ℃), and high thermal expansion coefficients (TEC &gt; 11.0×10⁻⁶ K⁻¹ at 1500 ℃) further supported their potential application as protective coating materials.

A combined study on structural, magnetic and specific heat on double perovskite iridates Ln2CoIrO6 [Ln = Pr, Nd

We report rich magnetic behavior for Co–Ir based double perovskites consisting of different rare earth cations Pr and Nd: Pr2CoIrO6 (PCIO) and Nd2CoIrO6 (NCIO). Both oxides show an antisite disorder of 10% and a ferrimagnetic transition, T around 96 K and 98 K respectively. The long range magnetic ordering is arising from the canted antiferromagnetic ordering between the Co2+ and Ir4+ ions. A prominent peak around 27 K in magnetization data of NCIO indicates that the total moment of Nd ion is antiferromagnetically coupled to the Co–Ir sublattice. The long range order of the Nd sublattice is corroborated by the evidence of an anomaly in specific heat at very low temperature. The compounds exhibit a maximum change of magnetic entropy of 0.57 (0.48) J kg.K−1 at T in a magnetic field of 5 T. The strong spin–orbit coupling in 5d states of Ir and cation disorder lead to the Mott insulating phase as found from the analysis of temperature dependent resistivity. These unique behaviors suggest an interesting interplay between localized Pr/Nd-4f, itinerant Co-3d and Ir-5d electrons.

Effect of heteroatoms on the binding properties of preorganized claw-type phenanthroline-based ligands towards lanthanide cations

Rational design of highly selective ligands is important for recovering of rare earth elements (REEs) from alternative sources which could be beneficial for the current REEs production in many aspects such as reducing the production cost, relieving the environmental influence and also serving as guidelines for specific REEs binding ligand design. While the complicated coordination properties and the uncertain coordination number of REEs hinder the search for high-selective binding ligands. Current ligand designs are mostly based on trial-and-error method. Structure-function relationship is thus highly desired. In this work, we designed three claw-type phenanthroline ligands with structural differences only on the non-coordination sites. By changing the substituents from benzo[d]imidazole to benzo[d]thiazole and benzo[d]oxazole, the effects of heteroatoms on ligand solid-state packing, photophysics and binding properties were demonstrated. The benzo[d]imidazole flanked phenanthroline ligand showed the most promising sensing ability towards La (III) and Eu (III) with high limit-of-detections of 0.25 and 0.23 μM in methanol. On the other side, benzo[d]thiazole and benzo[d]oxazole decorated ligands showed no and little discrimination ability towards REEs. This study revealed the important role of heteroatoms on the selectivity of the ligands and could contribute to the rational design of high-selective ligands for lanthanides, especially light lanthanides.

Yttrium separation by phosphorylcarboxylic acid and the underlying tetrad effect along lanthanide unveiled from different microscopic interactions

Due to similar physical and chemical properties, separating and purifying rare earth elements is challenging. Considering the environmental issue, the design and synthesis of efficient and green extractants are significant for this purpose. To this end, the underlying complexation between rare earth and the extractant should be clarified, and the long-historically existing tetrad effect along with the lanthanide family from La to Lu due to the different 4f orbital occupations should be figured out. Thus, within this study, taking our newly experimentally synthesized extractant, phosphorylcarboxylic acid, as an example and utilizing accurate quantum mechanical calculation, we comprehensively investigated the complexation behavior between rare earth and the extractant via the quantum theory of atoms in molecules (QTAIM), Mayer bond order (MBO), molecular orbital (MO) energy level, natural bond orbital (NBO), charge decomposition analysis (CDA), electron localization function (ELF) and extended transition state-natural orbitals for chemical valence (ETS-NOCV). It has been found that yttrium can be separated from the lanthanide series by the phosphorylcarboxylic acid, attributed to the poor ability of Y3+ to accept electrons and the weak orbital interactions compared to other rare earth cations. This paper also reveals the tetrad effect caused by the different occupations of 4f orbital electrons, providing a theoretical approach to comprehending the diverse extraction behaviors in the rare earth extraction process.

Effect of the effective refractive index on the radiative decay rate in nanoparticle thin films.

In this work, we theoretically and experimentally study the influence of the optical environment on the radiative decay rate of rare-earth transitions in luminescent nanoparticles forming a thin film. We use electric dipole sources in finite-difference time-domain simulations to analyze the effect of modifying the effective refractive index of transparent layers made of phosphor nanocrystals doped with rare earth cations, and propose a correction to previously reported analytical models for calculating the radiative decay rate. Our predictions are tested against an experimental realization of such luminescent films, in which we manage to vary the effective refractive index in a gradual and controllable manner. Our model accurately accounts for the measurements attained, allows us to discriminate the radiative and non-radiative contributions to the time-resolved photoluminescence, and provides a way to rationally tune the spontaneous decay rate and hence the photoluminescence quantum yield in an ensemble of luminescent nanoparticles.

Assemblies of poly(N-vinyl-2-pyrrolidone)-based double hydrophilic block copolymers triggered by lanthanide ions: characterization and evaluation of their properties as MRI contrast agents.

Because of the formation of specific antibodies to poly(ethylene glycol) (PEG) leading to life-threatening side effects, there is an increasing need to develop alternatives to treatments and diagnostic methods based on PEGylated copolymers. Block copolymers comprising a poly(N-vinyl-2-pyrrolidone) (PVP) segment can be used for the design of such vectors without any PEG block. As an example, a poly(acrylic acid)-block-poly(N-vinyl-2-pyrrolidone) (PAA-b-PVP) copolymer with controlled composition and molar mass is synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Mixing this copolymer with lanthanide cations (Gd3+, Eu3+, Y3+) leads to the formation of hybrid polyion complexes with increased stability, preventing the lanthanide cytotoxicity and in vitro cell penetration. These new nanocarriers exhibit enhanced T1 MRI contrast, when intravenously administered into mice. No leaching of gadolinium ions is detected from such hybrid complexes.

Approaches to the design of efficient and stable catalysts for biofuel reforming into syngas: doping the mesoporous MgAl2O4 support with transition metal cations.

The mesoporous MgAl2O4 support is promising for the design of efficient and stable to coking catalysts for natural gas and biofuel reforming into syngas. This work aims at doping this support with transition metal cations (Fe, Cr, Ti) to prevent the incorporation of Ni and rare-earth cations (Pr, Ce, Zr), loaded by impregnation, into its lattice along with providing additional sites for CO2 activation required to prevent coking. Doped MgAl1.9Me0.1O4 (Me = Fe, Ti, Cr) mesoporous supports prepared by the one-pot evaporation-induced self-assembly method with Pluronic P123 triblock copolymers were single-phase spinels. Their specific surface area varies in the range of 115-200 m2 g-1, decreasing to 90-110 m2 g-1 after successive addition of the supporting nanocomposite active component 10 wt% Pr0.3Ce0.35Zr0.35O2 + (5 wt% Ni + 1% Ru) by impregnation. Mössbauer spectroscopy for iron-doped spinels confirmed the spatially uniform distribution of Fe3+ cations in the lattice without clustering being mainly located at the octahedral positions. Fourier-transform infrared spectroscopy of the adsorbed CO molecules was performed to estimate the surface density of metal sites. In methane dry reforming, the positive effect of MgAl2O4 support doping was observed from both a higher turn-over frequency as compared with the catalyst on the undoped support as well as the highest efficient first-order rate constant for the Cr-doped catalyst as compared with published data for a variety of Ni-containing catalysts based on the alumina support. In the reaction of ethanol steam reforming, the efficiency of catalysts on the doped supports is comparable, while exceeding that of Ni-containing supported catalysts reported in the literature. Coking stability was provided by a high oxygen mobility in the surface layers estimated by the oxygen isotope heteroexchange with C18O2. A high efficiency and coking stability were demonstrated in the reactions of methane dry reforming and ethanol dry and steam reforming in concentrated feeds for the honeycomb catalyst with a nanocomposite active component on the Fe-doped MgAl2O4 support loaded on the FeCrAl-alloy foil substrate.

Magnetic and optical studies of a new family of multidimensional and multiproperty PO-lanthanide(III) derived systems.

A new family of lanthanide compounds has been synthesized using 1,2-bis(diphenylphosphino)ethane dioxide (dppeO2) as an O-donor ligand through the phosphoryl group to lanthanide(III) cations and structurally, magnetically and optically studied. Depending on the lanthanide, two different topologies appear: the two-dimensional structure [LnIII(dppeO2)1.5(NO3)3(H2O)0.5]n (Ln = Ce (1), Sm (2) and Dy (6)) and the one-dimensional structure [Ln(dppeO2)(NO3)3DMF]n (Ln = Eu (3), Gd (4) and Tb (5)). Some of the Ln-derived complexes have been used as structural probes, while others have been synthesized to use the specific characteristics of each cation to take advantage of their magnetic/luminescence properties. Complex 6 presents slow relaxation of the magnetization while 2, 3 and 5 present emitting properties in the visible range.

Color-tunable emissions realized by Tb3+ to Eu3+ energy transfer in ZnGdB5O10 under near-UV excitation.

Photoluminescent (PL) energy transfer (ET) between two typical rare earth activators Tb3+ and Eu3+ is utilized to achieve color-tunable emission and the color range is apparently dependent on the ET efficiency. In the target host ZnGdB5O10 (ZGBO), the relatively low symmetric coordination environment of the rare earth cation not only suppresses the parity-forbidden law of the 4f-4f transitions of Tb3+ in the near-UV region, but also enhances the internal quantum efficiency (IQE), where the optimal IQE is 65.61% for ZGBO:0.8Tb3+. Moreover, its ET to Eu3+ is highly efficient, i.e. 94.71% in ZGBO:0.8Tb3+,0.10Eu3+, which eventually leads to a wide range of color-tunable emissions from green (0.2915, 0.5915) to red (0.6207, 0.3731). The systematic PL spectral study on Tb3+/Eu3+ singly doped and co-doped phosphors suggests that the ET mechanism takes place through the electric dipole-dipole interaction according to the Inokuti-Hirayama (I-H) model. Additionally, the in situ high temperature PL spectra indicate the very high thermal stability of ZnGd0.19Tb0.8Eu0.01B5O10, indicating that it can be a potential candidate for near-UV light emitting diode-pumped phosphors.

Structural characterization, phase analysis and electrochemical hydrogen storage studies on new pyrochlore SmRETi2O7 (RE = Dy, Ho, and Yb) microstructures

A modified solid-state method was used to synthesize new SmRETi2O7 pyrochlores. The new samples were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy dispersive x-ray (EDX), Fourier transform infrared (FT-IR) and Raman spectroscopy. Qualitative and quantitative analyses were done by MAUD software to obtain crystallographic parameters. Based on the results, the crystal system of the new SmRETi2O7 pyrochlores was cubic with Fd3m space group. A slight shift in the Bragg positions was observed which was related to the cationic radii of the rare earth cations. The correlation between the structural parameters and the crystallographic data was also done. Besides, the electrochemical hydrogen storage (EHS) capacity of these pyrochlores were investigated. The holmium-containing oxide structure (SmHoTi2O7) compared to other samples exhibited a higher discharge capacity, about 1340 mAh/g. The results of EHS studies well correlated with the crystallographic data.

Salt-flux growth of HoCuMg4 single crystals.

Polycrystalline samples of the magnesium-rich intermetallic compounds RECuMg4 (RE = Dy, Ho, Er, Tm) were synthesized by reaction of the elements in sealed tantalum ampoules heated in a high-frequency induction furnace. Phase purity of the RECuMg4 phases was ascertained by powder X-ray diffraction patterns. Well-shaped single crystals of HoCuMg4 could be grown in a NaCl/KCl salt flux and the crystal structure was refined from single crystal X-ray diffraction data: TbCuMg4 structure-type, space group Cmmm, a = 1361.4(2), b = 2039.3(4), c = 384.62(6) pm. The crystal structure of the RECuMg4 phases can be understood as a complex intergrowth variant of CsCl and AlB2 related slabs. The remarkable crystal chemical motif concerns the orthorhombically distorted bcc-like magnesium cubes with Mg-Mg distances ranging from 306 to 334 pm. At high temperatures DyCuMg4 and ErCuMg4 are Curie-Weiss paramagnets with paramagnetic Curie-Weiss temperatures of -15 K and -2 K for RE = Dy and Er, respectively. The effective magnetic moments, 10.66μB for RE = Dy and 9.65μB for RE = Er prove stable trivalent ground states for the rare earth cations. Magnetic susceptibility and heat capacity measurements reveal long-range antiferromagnetic ordering at low temperatures (<21 K). Whereas DyCuMg4 exhibits two subsequent antiferromagnetic transitions at TN = 21 and 7.9 K which successively remove half of the entropy of a doublet crystal field ground state of Dy, ErCuMg4 shows a single, possibly broadened, antiferromagnetic transition at 8.6 K. The successive antiferromagnetic transitions are discussed with respect to magnetic frustration in the tetrameric units present in the crystal structure.