A luminescence study of B-type Eu2O3 under pressure

Abstract

Luminescence spectra from Eu³ + ion in B-type (monoclinic) ₂O₃ powder have been recorded at room temperature as a function of pressure using a diamond anvil cell. Changes in the spectral pattern of the Eu³ + ion emission at about 4 GPa indicated that a phase transition to the A-type (hexagonal) structure had taken place. Upon release of the applied pressure, the B-type structure was regained with hysteresis. The spectral shifts with pressure have been used to study the effect of pressure on the spin-orbit interaction of the 4f electrons in the Ed + ion. The relationship between the relative changes in the spin-orbit coupling constant, ζ_4f, and the volume accompanying the phase transition is also discussed.     

Hydrothermal synthesis, structure, and magnetic properties of Pu(SeO3)2

The reaction between PuO₂ and SeO₂ under mild hydrothermal conditions results in the formation of Pu(SeO₃)₂ as brick-red prisms. This compound adopts the Ce(SeO₃)₂ structure type, and consists of one-dimensional chains of edge-sharing [PuO₈] distorted bicapped trigonal prisms linked by [SeO₃] units into a three-dimensional network. Crystallographic data: Pu(SeO₃)₂, monoclinic, space group P2₁/n, a=6.960(1) Å, b=10.547(2) Å, c=7.245(1) Å, β=106.880(9)°, V=508.98(17) Å³, Z=4 (T=193 K), R(F)=2.92% for 83 parameters with 1140 reflections with I>2σ(I). Magnetic susceptibility data for Pu(SeO₃)₂ are linear from 35 to 320 K and yield an effective moment of 2.71(5) μ_B and a Weiss constant of −500(5) K.     

Variation in the Luminescence Lifetimes of Eucl3·nH2O(N=0,L,2,3,6)

Eu³⁺ ion emission spectra and luminescence lifetimes were investigated for EuCl₃ -nH₂O (n=0,1,2,3,6). Each compound exhibited a characteristic set of emission bands and a specific luminescence lifetime. The number of water molecules and chloride ions coordinated to the Eu³⁺ ion in these materials was estimated from the observed lifetimes, spectroscopic implications, and expected lanthanide coordination numbers. Approximation of the observed luminescence decay constant for each material was possible through the use of arithmetic terms associated with both the complexed water molecules and the complexed chloride ions which make up the inner-coordination sphere of the Eu³⁺ ion.     

Synthesis and structure of In(IO3)3 and vibrational spectroscopy of M(IO3)3 (M=Al, Ga, In)

The reaction of Al, Ga, or In metals and H₅IO₆ in aqueous media at 180 °C leads to the formation of Al(IO₃)₃, Ga(IO₃)_3, or In(IO₃)₃, respectively. Single-crystal X-ray diffraction experiments have shown In(IO₃)₃ contains the Te₄O₉-type structure, while both Al(IO₃)₃ and Ga(IO₃)₃ are known to exhibit the polar Fe(IO₃)₃-type structure. Crystallographic data for In(IO₃)₃, trigonal, space group , a=9.7482(4) Å, c=14.1374(6) Å, V=1163.45(8) Z=6, R(F)=1.38% for 41 parameters with 644 reflections with I>2σ(I). All three iodate structures contain group 13 metal cations in a distorted octahedral coordination environment. M(IO₃)₃ (M=Al, Ga) contain a three-dimensional network formed by the bridging of Al³⁺ or Ga³⁺ cations by iodate anions. With In(IO₃)₃, iodate anions bridge In³⁺ cations in two-dimensional layers. Both materials contain distorted octahedral holes in their structures formed by terminal oxygen atoms from the iodate anions. The Raman spectra have been collected for these metal iodates; In(IO₃)₃ was found to display a distinctively different vibrational profile than Al(IO₃)₃ or Ga(IO₃)₃. Hence, the Raman profile can be used as a rapid diagnostic tool to discern between the different structural motifs.     

Product evolution in the Np(IV) fluorophosphate system

The reaction of ²³⁷NpO₂ with Cs₂CO₃, Ga₂O₃, H₃PO₄, and HF under mild hydrothermal conditions leads to the formation of NpFPO₄ after 4 days at 180 °C. Heating at 180 °C for an additional 6 days leads to the crystallization of Cs₂Np₂F₇PO₄ and NpF₄. The Ga₂O₃ forms a GaPO₄ matrix in which crystals of NpFPO₄, Cs₂Np₂F₇PO₄, and NpF₄ grow. Single crystal X-ray data reveal that the structure of NpFPO₄ consists of Np(IV) centers bound by both fluoride and phosphate to yield [NpF₂O₆] distorted dodecahedra. These are linked by corner-sharing with fluoride and both corner- and edge-sharing with phosphate to yield a dense, three-dimensional network. The structure of Cs₂Np₂F₇PO₄ is complex and contains both distorted dodecahedral [NpO₂F₆] and tricapped trigonal prismatic [NpO₂F₇] environments around Np(IV) that are linked with each other through corner- and edge-sharing, and with the phosphate groups to create a three-dimensional structure. There are small channels extending down the a-axis in Cs₂Np₂F₇PO₄. Crystallographic data: NpFPO₄, orthorhombic, space group Pnma, a=8.598(2), b=6.964(1), c=6.337(1) Å, Z=4, V=379.44(13) Å³, R(F)=3.53% for 40 parameters and 465 reflections with I>2σ(I) (T=193 K); Cs₂Np₂F₇PO₄, monoclinic, space group P2₁/c, a=8.8727(4), b=16.2778(7), c=7.8009(4) Å, β=112.656(1), Z=4, V=1039.73(8) ų, R(F)=2.27% for 146 parameters and 2465 reflections with I>2σ(I) (T=193 K).     

Selected systematic properties and some recent investigations of actinide metals and alloys

The actinide elements form a unique and scientifically interesting series. They display a wide range of physical properties from those characteristic of d-electron transition metals to those of the 4f electron, lanthanide metals. This article provides a brief summary of some important properties of the actinide elements and discusses how the changing role of the 5f electrons influences these properties. Recent results from studies on the actinides and extrapolated values of others have been incorporated into the presented systematics. Finally, some recommendations for future studies of the actinides are presented.     

Photoluminescence and Raman studies of Sm3+ and Nd3+ ions in zirconia matrices: example of energy transfer and host-guest interactions

Photoluminescence and Raman studies on Sm(3+)- and Nd(3+)-doped zirconia are reported. The Raman studies indicate that the monoclinic (m) phase dominates up to a 10 at.% lanthanide level, while stabilization of the cubic phase is attained at approximately 20 and approximately 25 at.% of Sm(3+) and Nd(3+), respectively. Both systems are strongly luminescent under photo-excitation. The emission spectrum at 77 K of the ZrO(2):Sm(3+) system consists of a broad band at 505 nm, that corresponds to the zirconia matrix. At room temperature the band maximum blue-shifts to 490 nm. Sharper bands corresponding to f-f transitions within the Sm(3+)ion are also exhibited in the longer wavelength region of the spectrum. Exclusive excitation of the zirconia matrix provides sensitized emission from the acceptor Sm(3+) ion. The excitation profile is dominated by a broad band at 325 nm when monitored either at the zirconia or at one of the Sm(3+) emissions. A spectral overlap between the 6H(5/2)-->(4)G(7/2) absorption of the Sm(3+) ion with the zirconia emission leads to an efficient energy transfer process in the systems. Multiple facets of the spectral behavior of the Sm(3+) or Nd(3+) in the zirconia matrices, as well as the effects of compositions on the emission and Raman properties of the materials, and the role of defect centers in photoluminescence and the energy transfer processes are discussed.