The luminescence of CaYBO4:RE (REEu, Gd, Tb, Ce) in VUV-visible region

Phosphors CaYBO₄:RE³⁺ (RE=Eu, Gd, Tb, Ce) were synthesized with the method of solid-state reaction at high temperature, and their vacuum ultraviolet (VUV)-visible luminescent properties in VUV-visible region were studied at 20 K. In CaYBO₄, it is confirmed that there are two types of lattice sites that can be substituted by rare-earth ions. The host excitation and emission peaks of undoped CaYBO₄ are very weak, which locate at about 175 and 350-360 nm, respectively. The existence of Gd³⁺ can efficiently enhance the utilization of host absorption energy and result in a strong emission line at 314 nm. In CaYBO₄, Eu³⁺ has typical red emission with the strongest peak at 610 nm; Tb³⁺ shows characteristic green emission, of which the maximum emission peak is located at 542 nm. The charge transfer band of CaYBO₄:Eu³⁺ was observed at 228 nm; the co-doping of Gd³⁺ and Eu³⁺ can obviously sensitize the red emission of Eu³⁺. The fluorescent spectra of CaYBO₄:Ce³⁺ is very weak due to photoionization; the co-addition of Ce³⁺-Tb³⁺ can obviously quench the luminescence of Tb³⁺.     

Luminescent polymeric hybrids functionalized by β-diketone with silicon-oxygen networks and carbon chains: Assembly and characterization

2-Thenoyltrifluoroacetone (TTA) was grafted onto the coupling agent 3-(triethoxysilyl)-propyl-isocyanate to construct the precursor I (TTA-Si), and polymer precursors II (PVPD, PMAA and PVPDMAA) were synthesized through the addition polymerization reactions. Then precursors I and II have coordinated to the rare-earth ions with the carbonyl, carboxyl group or nitrogen atom, respectively, and after hydrolysis and copolycondensation sol-gel process, the three kinds of polymeric hybrids were obtained. FTIR, ultraviolet-visible diffuse reflection and fluorescence absorption spectra, electronic micrographs, room-temperature X-ray diffraction patterns and TG plots were characterized and the results reveal that the hybrid materials showed uniformity in the microstructure, efficient intramolecular energy transfer system and excellent characteristic emission of terbium ions under UV irradiation.     

Palladium(II)–rare-earth metal(III) paddlewheel carboxylate complexes: Easy total acetate to pivalate metathesis

Bis-paddlewheel heterobimetallic complexes in which palladium(II) is connected to the rare-earth metals(III) [Pd(μ-OOCMe)₄Ln(OH₂)(μ,η²-OOCMe)]₂ × 2HOOCMe (Ln = Nd, Sm, Eu, Yb and Tm) by four acetate bridges were synthesised by the reaction of Pd₃(μ-OOCMe)₆ with the Ln^III acetates. The tetraacetate-bridged complexes were unexpectedly found to be readily transformed by the stoichiometric amount of pivalic acid into the mono-paddlewheel tetrapivalate-bridged analogues in which the paddlewheel structure [Pd(μ-OOCR)₄Ln] maintains as established by X-ray crystallography. The role of the intra- and intermolecular H-bonding in these complexes is discussed.     

The new ternary pnictides Er12Ni30P21 and Er13Ni25As19: Crystal structures and magnetic properties

The new ternary pnictides Er₁₂Ni₃₀P₂₁ and Er₁₃Ni₂₅As₁₉ have been synthesized from the elements. They crystallize with hexagonal structures determined from single-crystal X-ray data for Er₁₂Ni₃₀P₂₁ (space group P6₃/m, a=1.63900(3) nm, c=0.37573(1) nm, Z=1, R_F=0.062 for 1574 F-values and 74 variable parameters), and for Er₁₃Ni₂₅As₁₉ (Tm₁₃Ni₂₅As₁₉-type structure, space group P6?, a=1.6208(1) nm, c=0.38847(2) nm, Z=1, R_F=0.026 for 1549 F-values and 116 variable parameters). These compounds belong to a large family of hexagonal structures with a metal-metalloid ratio of 2:1. HRTEM investigations were conducted to probe for local ordering of the disordered structure at the nanoscale. The magnetic properties of the phosphide Er₁₂Ni₃₀P₂₁ have been studied in the temperature of range 2<T<300 K and with applied fields up to 5 T. The magnetic susceptibility follows the Curie-Weiss law from 4 to 300 K. The measured value of μ_eff=9.59 μ_B corresponds to the theoretical value of Er³⁺.     

Photoluminescence spectra of thenardite Na2SO4 activated with rare-earth ions, Ce, Sm, Tb, Dy and Tm

Five Na₂SO₄:RE³⁺ phosphors activated with rare-earth (RE) ions (RE³⁺=Ce³⁺, Sm³⁺, Tb³⁺, Dy³⁺ and Tm³⁺) were synthesized by heating natural thenardite Na₂SO₄ from Ai-Ding Salt Lake, Xinjiang, China with small amounts of rare-earth fluorides, CeF₃, SmF₃, TbF₃, DyF₃ and TmF₃, at 920 °C in air. The photoluminescence (PL) and optical excitation spectra of the obtained phosphors were measured at 300 and 10 K. In the PL spectrum of Na₂SO₄:Ce³⁺ at 300 K, two overlapping bands with peaks at 335 and 356 nm due to Ce³⁺ were first observed. Narrow bands observed in PL and excitation spectra of Na₂SO₄:RE³⁺ (RE³⁺=Sm³⁺, Tb³⁺, Dy³⁺ and Tm³⁺) phosphors were well identified with the electronic transitions within the 4fⁿ (n=5, 8, 9 and 12) configurations of RE³⁺. The existence of excitation bands with high luminescence efficiency at wavelengths shorter than 230 nm is characteristic of Na₂SO₄:RE³⁺ (RE³⁺=Sm³⁺, Tb³⁺, Dy³⁺ and Tm³⁺) phosphors. The obtained results suggest that these phosphors are unfavorable as the phosphor for usual fluorescence tubes, i.e., mercury discharge tubes, but may be favorable as the phosphor for UV-LED fluorescent tubes and as cathodoluminescence, X-ray luminescence and thermoluminescence phosphors.     

Control of mixed protonic and electronic conductivity by mixing rare-earth ortho-borates

In order to develop mixed protonic and electronic conductors, we proposed a novel concept for material design that enables to control partial conductivities by fabricating solid solutions of protonic and electronic conductors. In this work, Sr-doped LaBO₃ and Sr-doped CeBO₃ were chosen as model compounds conducting protons and electron holes, respectively. Solid solutions of the above borates, Sr-doped La_1 − xCe_xBO₃, were prepared, and their electrical conductivities were investigated in 8.5 × 10²-4.2 × 10³ Pa of p(H₂O) and 1.0 × 10-1.0 × 10⁵ Pa of p(H₂) at 1073 K. From the experimental results of the gas partial pressure dependences of the conductivities, major charge carrier species were identified as a function of x. It was found that proton was the major charge carrier when x < 0.2 while the contribution of the electron hole conduction became remarkable as x increased above 0.2. The contribution of the electron hole conduction can be interpreted by the percolation model.     

Enhanced photoluminescence of rare-earth doped films prepared by off-axis pulsed laser deposition

Alternate pulsed laser deposition from the host (Al₂O₃) and dopant (Er, Yb) targets has been used to prepare artificially nanostructured films in which the rare earth ion-ion separation is controlled in the nanometer scale in order to control energy transfer between ions. One series of films was prepared in the standard on-axis configuration, i.e. a static substrate being centred with respect to the plasma expansion axis. A second series of films was prepared by rotating the substrate with respect to a shifted axis parallel to the plasma expansion one (off-axis configuration). The latter configuration leads to films with enhanced thickness and Er related photoluminescence intensity uniformity. More interestingly, the Er related photoluminescence lifetime in as-grown films increases up to 2.5 ms, which is much higher than the maximum value of 1 ms obtained for the on-axis configuration films. This enhancement is discussed in terms of a decrease of defect density when using the off-axis configuration.     

First-principles study of electronic structure and magnetism of cubic Al1−xErxN using the LSDA+U approach

First-principles calculations, by means of the full-potential augmented plane wave method using the LSDA+U approach (local spin density approximation with Hubbard-U corrections), have been carried out for the electronic structure of the Al_0.75Er_0.25N. The LSDA+U method is applied to the rare-earth 4? states. We have investigated the electronic and magnetic properties.The Al_0.75Er_0.25N is shown to be a semiconductor, where the filled ? states are located in the valence bands and the empty ones above the conduction band edge. The magnetic interaction of the rare-earth ion with the host states at the valence and conduction band edges has been investigated and discussed.     

Field and temperature induced colossal strain in Gd5(SixGe1−x)4

Gd₅(Si_xGe_1−x)₄, known for its giant magnetocaloric effect, also exhibits a colossal strain of the order of 10,000 ppm for a single crystal near its coupled first-order magnetic-structural phase transition, which occurs near room temperature for the compositions 0.41≤x≤0.575. Such colossal strain can be utilised for both magnetic sensor and actuator applications. In this study, various measurements have been carried out on strain as a function of magnetic field strength and as a function of temperature on single crystal Gd₅Si₂Ge₂ (x=0.5), and polycrystalline Gd₅Si_1.95Ge_2.05 (x=0.487) and Gd₅Si_2.09Ge_1.91 (x=0.52). Additionally a giant magnetostriction/thermally induced strain of the order of 1800 ppm in polycrystalline Gd₅Si_2.09Ge_1.91 was observed at its first order phase transition on varying temperature using a Peltier cell without the use of bulky equipment such as cryostat or superconducting magnet.     

Hard magnetic properties of anisotropic Sm-Fe-N magnets produced by compression shearing method

Anisotropic Sm-Fe-N bulk magnets were produced by the compression shearing method using a hardened steel plate and a tungsten-carbide (WC) plate. It was found that the magnets retained the original Sm₂Fe₁₇N₃ phase structure without any appreciable decomposition of the Sm₂Fe₁₇N₃ phase. The anisotropic Sm-Fe-N bulk magnet produced using a WC plate had a higher density and higher crystallographic alignment of the Sm₂Fe₁₇N₃ phase than that produced using a hardened steel plate, and exhibited high maximum energy products of 228 kJ/m³ with a high coercivity of 0.88 MA/m.