Rare earth compounds

Communicated by Satoshi Uda Keywords: A1. X-ray diffraction A2. Growth from high temperature solutions A2. Single crystal growth B1. Rare earth compounds B1. Vanadates B2. Nonlinear optic materials a b s t r a c t Large LuVO 4 single crystals have been successfully obtained by high-temperature solution method. The structure details of these crystals are determined by X-ray crystallographic analysis and Raman spec-troscopy. It is observed that the crystal consists of LuVO 4 phase with trace amount of imperfections possibly due to oxygen vacancies. The optical quality of the crystal is assessed by Spectroscopic Ellipsometry (SE). The crystal shows higher than +0.2 birefringence in a large interval of wavelengths.

Silicon dioxide-based nanocomposites have shown great potential in novel chemical and biological sensor development due to their large loading capacity and high surface area to volume ratio for trapping molecular complexes of various sizes. However, their potential applications in forensic science, latent fingerprint detection in particular, were still unclear. In this study, we have succeeded in trapping the highly fluorescent and photo-stable Eu 3+ metal ions/sensitizer complex in silicon dioxide-based nanocomposites, doped xerogels, using the sol-gel method. We have tested the spectroscopic properties of Eu 3+ in several combinations of rare earth sensitizers and different derivatives of silicon dioxide nanoporous templates. Our results indicated that the use of 1,10-phenanthroline (OP) sensitizer in tetraethoxysilane (TEOS) template provides the best fluorescently doped xerogels applicable for latent fingerprint detections on various forensic relevant materials, including metal foil, glass, plastic, colored paper, and a green tree leaf. The fabrication procedure, UV/vis and fluorescence characterizations, and fingerprint labeling results of these new Eu 3+ /OP/TEOS nanocomposites are presented in this exploratory study.

Single crystals of RVO 4 (R ¼ Y,Gd) doped with optically active element like Nd have been obtained under mild hydrothermal conditions (T ¼ 240 1C, P$80 bars). A detailed mechanism of the crystallization process, which helps in the considerable reduction of the PT conditions of the growth of these high-melting (m.p.41800 1C) crystals has been formulated. The crystals obtained have been subjected to morphological, X-ray powder diffraction and infrared spectroscopic studies.

The structural and magnetic properties of doubly substituted Nd 2 Fe 17−x−y Ti x Ga y (0 ≤ x ≤ 1.0, 0 ≤ y ≤ 3) compounds have been investigated by a combined technique of X-ray diffraction, neutron diffraction and magnetic measurements. Rietveld refinements of the diffraction data indicate that all the samples crystallize in the rhombohedral Th 2 Zn 17-type structure. For a given Ti content (x), the lattice parameters a and c, and unit cell volume V of Nd 2 Fe 17−x−y Ti x Ga y all increase linearly with increasing Ga content. The addition of Ti initially has a considerably positive effect on the increasing rates of a, c, and unit cell volume V, but later the effect becomes very slight and even negative with the further increase of Ti content. The site occupancies of Ti and Ga in the crystallographic sites change a little compared to what is observed in the corresponding singly substituted compounds. The effects of Ti and Ga on the bond lengths of the doubly substituted compounds are quite different from that of the singly substituted compounds. Magnetic measurements show the T C of Nd 2 Fe 17−x−y Ti x Ga y increases with increasing Ti content for a low Ga content while it behaves conversely for a higher Ga content. The T C of Nd 2 Fe 17−x−y Ti x Ga y increases with increasing Ga content for a particular Ti content, while the addition of Ti results in a slower increase of T C on the Ga content (y ≤ 3). For a given Ti content, the M s of Nd 2 Fe 17−x−y Ti x Ga y first increases a little and then decreases with the increase of Ga content, while for a given Ga content the M s of Nd 2 Fe 17−x−y Ti x Ga y decreases with the increase of Ti content.

New compounds of composition R3Pt4Ge13 have been successfully prepared with R = Dy, Ho, Er and Lu, by high-pressure (5-7 GPa) and high-temperature synthesis (up to 1073 K). Structural analysis confirms that all compounds crystallize in a non-centrosymmetric monoclinic structure (space group Cc). The magnetic properties of these four new compounds were studied, as well as those of Gd3Pt4Ge13 , a known compound on which few physical studies have been published. The magnetic susceptibility of the Gd, Dy, Ho and Er compounds follow a Curie-Weiss law in the temperature range 20 K-300 K, consistent with a trivalent state of the R ions. At lower temperature, magnetization and heat capacity measurements reveal antiferromagnetic ordering in Gd3Pt4Ge13 (TN = 6.2 ± 0.1 K) and a ferromagnetic one in Er3Pt4Ge13 (TC = 2.2 ± 0.1 K). Dy3Pt4Ge13 presents a magnetic order at
T* = 1.8 ± 0.2 K. Ho3Pt4Ge13 behaves as a Van Vleck type paramagnet below 10 K and Lu3Pt4Ge13 is found to be diamagnetic between 2 K and 300 K. This last compound shows no superconducting transition down to 400 mK.

A two-stage nuclear demagnetization refrigerator with large cooling capacity has been constructed and successfully operated. The first stage consists of 11 moles of the Van Vleck paramagnet PrNi5 in an initial field of 6 T, and the second stage consists effectively of 19 moles of copper in an initial field of Z6 T. The minimum temperature as measured with pulsed platinum NMR is 27 pK, the lowest ever obtained in a low-field experimental region.

Infrared-to-visible and infrared-to-infrared frequency upconversion processes in Yb 3+-Tm 3+ doped PbO-GeO 2 glasses containing silver nanoparticles ͑NPs͒ were investigated. The experiments were performed by exciting the samples with a diode laser operating at 980 nm ͑in resonance with the Yb 3+ transition 2 F 7/2 → 2 F 5/2 ͒ and observing the photoluminescence ͑PL͒ in the visible and infrared regions due to energy transfer from Yb 3+ to Tm 3+ ions followed by excited state absorption in the Tm 3+ ions. The intensified local field in the vicinity of the metallic NPs contributes for enhancement in the PL intensity at 480 nm ͑Tm 3+ : 1 G 4 → 3 H 6 ͒ and at 800 nm ͑Tm 3+ :

The crystal structure of the mineral tveitite-(Y) (Y 0.883 Na 0.106) • (Ca 0.841 LREE 0.159)(Ca 0.716 Na 0.204 HREE 0.080)(Ca 0.092 Na 0.074)F 6.952 from amazonite pegmatites of Rov-Gora Mountain (Keivy, Kola Peninsula) is determined using X-ray diffraction (Stoe IPDS diffractometer, λ Mo K α , graphite monochromator, 2 θ max = 63.5° , R = 0.051 for 1542 reflections). The main crystal data are as follows: a = 17.020(2) Å, c = 9.679(2) Å, V = 2428.2(4) Å 3 , space group , Z = 18, and ρ calcd = 4.00 g/cm 3. The idealized structural formula of the mineral is represented as (Y,Na) 6 (Ca, LREE) 6 (Ca,Na, HREE) 6 (Ca,Na)F 42 (Z = 3). The defect structure of the mineral manifests itself in a mixed occupation of all four independent cation positions and in a randomly disordered distribution of fluorine atoms over the majority of anion positions. It is shown that the crystal structure of tveitite-(Y) fulfills the function of an "Eratosthenes sieve" for yttrium cations and two groups of lanthanide cations, so that these cations are distributed over three different positions.

For many years, phosphor thermometry has been used for non-contact measurements in hostile high temperature environments, including large blackbody radiation backgrounds, vibration, rotation, fire/flame, pressure, or noise. Often these environments restrict the use of more common thermocouples or infrared thermometric techniques. In particular, temperature measurements inside jet turbines, rocket engines, or similar devices are especially amenable to fluorescence techniques. Often the fluorescent materials are used as powders, either suspended in binders and applied like paint or applied as high temperature sprays. These coatings will quickly assume the same temperature as the surface to which they are applied. The temperature dependence of fluorescent materials is a function of the base matrix atoms and a small quantity of added activator or "dopant" ions. Often for high temperature applications, the selected materials are refractory and include rare earth ions. Phosphors...

Green emitting SrGa 2 S 4 :Eu thin films have been prepared by reactive RF magnetron sputtering. Electron Probe MicroAnalysis, X-ray diffraction, Micro-Raman spectroscopy and roughness measurements were used to study the growth of SrGa 2 S 4 :Eu and to determine the effects of the post-deposition heat treatment on the morphological and structural properties. The post-deposition annealing is a necessary step for the layer crystallisation, it influences the film composition and the structural properties leading to the improvement of luminescence performances. Photoluminescence properties as a function of annealing parameters are reported.

Detectlon by posteuppreselon Ion exchange, as an adjunct to suppressed hydroxlde eluent Ion chromatography, Involves exchange of elutlng sample anlon or concurrently present Ht for a fluorescenthptkally absorbing anlon or catlon such as anthranllate or Cea+. Membrane-based postsuppresslon devices permlt rdlabk contlrmowr operattan, and detecttan limlts can be better than those attainable by conductlvity detwtlon.

The Mössbauer Effect(ME) is frequently used to investigate magnetically ordered systems. One usually assumes that the magnetic order induces a hyperfine magnetic field, B hyperf ine , at the ME active site. This is the case in the ruthenates, where the temperature dependence of B hyperf ine at 99 Ru sites tracks the temperature dependence of the ferromagnetic or antiferromagnetic order. However this does not happen in the rare-earth intermetallics, GdRu 2 and HoRu 2. Specific heat, magnetization, magnetic susceptibility, Mössbauer effect, and neutron diffraction have been used to study the nature of the magnetic order in these materials. Both materials are found to order ferromagnetically at 82.3 and 15.3 K, respectively. Despite the ferromagnetic order of the rare earth moments in both systems, there is no evidence of a correspondingly large B hyperf ine in the Mössbauer spectrum at the Ru site. Instead the measured spectra consist of a narrow peak at all temperatures which points to the absence of magnetic order. To understand the surprising absence of a transferred hyperfine magnetic field, we carried out ab initio calculations which show that spin polarization is present only on the rare-earth site. The electron spin at the Ru sites is effectively unpolarized and, as a result, B hyperf ine is very small at those sites. This occurs because the 4d Ru electrons form broad conduction bands rather than localized moments. These 4d conduction bands are polarized in the region of the Fermi energy and mediate the interaction between the localized rare earth moments.

, and Y) with variable oxygen content have been synthesized using the liquid mixing technique and have been analyzed by powder X-ray and neutron diffraction methods. A triple perovskite-type structure with ordered Ba and R cations and having the symmetry of space group P4/mmm was obtained only for R ‫؍‬ Y, Dy, and Er, whereas the larger R atoms gave the atomic arrangement of disordered, defective perovskites with average symmetry Pm3 m. No perovskite-type phases were obtained when Yb and Lu were tried. The oxygen content of the oxygen-saturated phases was found to increase with increasing size of the cation R from w ‫؍‬ 0.07 for Er to w ‫؍‬ 0.83 for La. The Ne´el temperature (&650 K) and the magnitude of the Fe magnetic moment (&3.3 B at room temperature) are highest when trivalent iron is involved (w ‫؍‬ 0), but these quantities are rather insensitive to the nature of R and to slight variations of oxygen content in the triple perovskite-type structure of the Y, Dy, and Er compounds. In the case of the cubic structures, however, both quantities depend strongly on the oxygen stoichiometry. In the magnetically ordered state, nearest-neighbor iron moments are coupled antiferromagnetically along the three crystallographic directions in all samples, resulting in magnetic structures with symmetry Immm and magnetic unit cells related to those of the corresponding nuclear structures by the transformation matrix (11 0/110/002).

Powder samples of hexagonal Laves phase ErMn 2 H x hydrides, with 0 < x ≤ 4.3, are characterised by X-ray analysis and SQUID magnetometry for temperatures ranging between 2 and 375 K. Structural transformations as function of the hydrogen concentration and temperature were observed. In particular, a decomposition of spinodal type has been found. It has been shown that structural transformations are reflected in the magnetic behaviour and that an increase of the Mn-Mn distance above the critical distance causes appearance of Mn magnetic moments. The analysis of the magnetic data as function of the hydrogen content, temperature and magnetic field shows that the Mn magnetic moments are antiferromagnetically coupled. The behaviour of these hydrides is compared with the properties of cubic hydrides.

Powder samples of TbMn H hydrides, with 0#x#4.3, are characterised by X-ray analysis and SQUID magnetometry for temperatures 2 x ranging between 2 and 375 K. We observed structural phase transformations as a function of the hydrogen concentration and temperature. In particular a spinodal decomposition for x,2 has been found. The structural transformations are reflected in the magnetic behaviour. The analysis of the magnetic data as a function of the hydrogen content, temperature and magnetic field shows that there are changes in antiferromagnetic ordering strongly influenced by the interactions between the Mn and Tb magnetic moments. Tentative magnetic and structural phase diagrams are proposed.

feedback Pb,~.Sn,Se/Pb,_,_,Eu,Sn,Se double heterostructure stripe geometry diode lasers were fabricated using molecular beam epitaxy. These lasers operated in the CW mode up to 90 K and in the pulse mode up to 100 K. They were unique in their low tuning rate with injection current 4 cm-'/A, and in that they withstood high CW injection currents without damage. These features are probably the result of the metal cladding layer located on top of the gratings.

has been studied by powder neutron diffraction below 100 K. The compound takes the hexagonal room temperature 1.78 structure at 100 and 50 K (P6 /mmc). At 2 K, below the antiferromagnetic ordering temperature of 10 K, there is a small orthorhombic 3d istortion of the lattice. The refined unit-cell dimensions at 2 K (space group Pnma) are a57.9505(2), b54.02502(14), c56.9823(2) A. The magnetic moments of Tb are 8.71(6) m , and are ordered antiferromagnetically along a. © 2002 Elsevier Science B. V. All rights B reserved.

To explore the limits of layer wound (RE)Ba 2 Cu 3 O 7-x (REBCO, RE = Rare Earth) coils in a high magnetic field environment > 30 T, a series of small insert coils have been built and characterized in background fields. One of the coils repeatedly reached 35.4 T using a single ~100 m length of REBCO tape wet wound with epoxy and nested in a 31 T background magnet. The coil was quenched safely several times without degradation. Contributing to the success of this coil was the introduction of a thin polyester film that surrounded the conductor. This approach introduces a weak circumferential plane in the coil pack that prevents conductor delamination that has caused degradation of several epoxy impregnated coils previously made by this and other groups.