P. Caro

Site Selective Spectroscopy and Structural Analysis of Yttria-Doped Zirconias

Abstract Yttria-stabilized zirconias Zr 1− x Y x O 2−0.5 x (tetragonal, cubic fluorite, and cubic C Ln 2 O 3 -type forms) are investigated by spectroscopic methods. Optically active europium ions that partially substitute yttrium ions act as a structural microprobe. Both conventional ultraviolet and dye laser (site-selective) excitation are used. The yttria-stabilized zirconias may be well described by a cationic sublattice in which tetravalent and trivalent cations are statistically distributed. The anionic sublattice accommodates vacancies at random on oxygen positions. These vacancies in turn cause complex oxygen displacements giving rise to what may be described as a “glass of anions.”

Interpretation of the optical absorption spectrum and of the paramagnetic susceptibility of neodymium A‐type sesquioxide

A‐Nd2O3 is a layer structure built on the (NdO)n+n cation. Data for the 4.2 K optical spectrum and the strongly anisotropic parallel and perpendicular paramagnetic susceptibilities between 4 and 1000 K measured on single crystals, are reproduced using a Hamiltonian, that involves 12 free atom parameters (three Racah’s parameters, the spin–orbit coupling constant, Trees’ parameters α and β, and Judd’s six Tk operators) and six C3v crystal field parameters. The Hamiltonian operates on the 364 kets in 4f3, that is including J mixing. 88 Stark levels (from 0 to 34 000 cm−1) were fitted to a mean square deviation of 17 cm−1. The crystal field parameters (Wybourne’s formalism) are B20=−836 cm−1, B40=634 cm−1, B43=−1606 cm−1, B60=752 cm−1, B63=237 cm−1, B66=672 cm−1. The spectrum is strongly displaced to the red with respect to Nd3+ in LaCl3 and this is due to a lowering of Slater’s integrals F2 and F4 by 2% to 3%. The F6 integral is unchanged. The spin–orbit coupling constant is also lowered by 2%. The interact...

Influence of J-mixing on the phenomenological interpretation of the Eu3+ ion spectroscopic properties

Abstract Two sets of Bkq crystal field parameters and Bγkq intensity parameters have been calculated from the transition occuring between the Stark levels of Eu3+ in KY3F10. One of the calculations includes the J-mixing; the other not. The influence of the J-mixing on the intensities of the “forbidden” transition 5D0 → 7F0 and on the hypersensitive transitions are analysed.

Rare-earth hydrides and rare-earth oxides in and from thin films of rare-earth metals

Abstract Thin films of rare-earth metals always getter hydrogen very easily under ordinary conditions of preparation. It is shown from X-ray and electron diffraction experiments that the f.c.c. hydrides appear as single-crystal inclusions especially in the case of the yttric series (except for ytterbium). The hydride inclusions yield conspicuous f.c.c. diffraction patterns which should not be mistaken for a rare-earth monoxide, LnO, or for an f.c.c. phase of the metal. Oxidation of the “metallic” thin films yields sesquioxide thin films. The electron diffraction pattern of C-type sesquioxides for large crystals in thin films exhibits “forbidden” diffraction spots which apparently do not agree with the recognized T7h space group. It is shown that these forbidden spots appear because of multiple diffraction effects.

Crystal field parameters for Eu3+ in KY3F10

The fluorescence spectrum of KY3F10: 1% Eu in powder form was recorded at 77 and 4.2°K between 4600 and 7000 A, and 89 fluorescence lines arising from levels 5D0, 5D1, 5D2, and probably 5D3 were observed. The spectrum agrees with with a C4v symmetry, and it is possible to determine the irreducible representation of the group associated with the Stark components of 2S+1LJ levels. The set of crystal field parameters agreeing best with the experiment, on a basis of 200 kets ‖7F≳, ‖5D≳, and ‖5G≳ of the 4f6 configuration, is B20=−551 cm−1, B04=−1360 cm−1, B44=+345 cm−1, B60=394 cm−1, and B64=234 cm−1.

Vibronic optical transitions in inorganic and organic rare earth materials

The lanthanide elements are widely used as optical structural probes in solid state chemistry. Group theory and line positions are used to derive the symmetry and the number of crystallographic sites. For some compounds additional lines or illogical splittings make interpretation difficult. The Stark level widths depend on the phonon density of states in the material: if it is a continuous function the classical theory applies well, but if the phonon density of states is resolved into sharp peaks, zero-phonon line splittings may occur from resonance effects, with sharp phonons corresponding to the energy difference between Stark levels. Examples are shown for lanthanide organic compounds, and for some inorganic phases as well. Vibronic satellites occur prominently in some phases, especially if tetrahedral anions (phosphate etc…) are present. From the vibronics associated with simple electronic transitions it is possible to derive an effective density of phonon states. The puzzling case of Eu3+ in GdNbO4, where the fine structure of the emission spectrum depends on the optical excitation wavelength, is presented.

Interpretation of the optical absorption spectrum and of the paramagnetic susceptibility of NdAlO3

The absorption spectrum of pure rhombohedral NdAlO3 was determined at 4.2 K from 10 000 to 34 000 cm−1. Adding the levels determined for the 4I multiplet by other authors, a total of 117 Stark levels was obtained. They were fitted to a mean square deviation of 13 cm−1 with a Hamiltonian involving 12 free atom parameters and six D3 crystal field parameters applied on the 364 kets basis in the 4f3 configuration. The values are B02=−481 cm−1, B04 =481 cm−1, B34=−390 cm−1, B06=−1700 cm−1, B36=−950 cm−1, B66=−1080 cm−1. Free atom parameters are very close to those of Nd3+ in LaCl3. The powder paramagnetic susceptibility was measured from 4 to 1000 K. The 1/χ versus T curve shows a pronounced curvature, even below 300 K, which is fairly well reproduced by a crystal‐field‐only calculation involving the complete wave vectors of the 18 lowest Kramers doublets.

Optical and structural investigation of the lanthanum β-alumina phase doped with europium

Abstract The lanthanum β-alumina phase doped with europium was investigated by X-ray diffraction and fluorescence. This nonstoichiometric phase exists over the composition range: 11 Al 2 O 3 1 La 2 O 3 to 14 Al 2 O 3 1 La 2 O 3 . The unit cell is hexagonal hexagonal with a = 5.560 ± 0.003 A, c = 22.001 ± 0.003 A and belongs to the P6 3 mmc space group. X-ray diffraction patterns do not vary between both boundary compositions, but fluorescence spectra show that the structure of the mirror plane in which the lanthanide ions are located is deeply modified. The atomic structure of the mirror plane is of “β-type” (like β(Na) or β(Ag)) for the lower alumina contents; it gradually changes to a “magnetoplumbite type” for higher alumina contents.

Crystal field effect and paramagnetic susceptibility of Na5Eu(MoO4)4 and Na5Eu(WO4)4

Fluorescence spectra have been analyzed at 4.2, 77, and 300 K and crystal field calculations have been performed on Na5Eu(MO4)4 (M=Mo, W) powders. The two sets of crystal field parameters are almost identical yielding a rms deviation of 5 cm−1. The values are (in cm−1): B20 =200 (180), B40 =−326 (−330), B44 =−863 (−852), B64 =−442 (−416), and B66 =−327 (−339) for Na4Eu(MoO4)4 and Na5Eu(WO4)4, respectively. Wave functions derived from the simulation were applied to the calculation of the temperature dependent paramagnetic susceptibility. Comparisons with experimental average paramagnetic susceptibilities, measured between 4.2 and 300 K, are very satisfactory.

Analysis and simulation of optical and magnetic properties of lanthanide aluminates LnMgAl11O19 (Ln=La/Nd,La/Eu,Pr) with magnetoplumbite‐like structure

Single crystals of LnMgAl11O19 aluminates with a magnetoplumbite‐like structure, (Ln=La1−xNdx, La1−x Eux, Pr), are grown by the flame fusion (Verneuil) or floating zone methods. Optical absorption or fluorescence spectra of these crystals reveal that Ln3+ ions occupy at least two or three different sites, instead of only one as in the ideal magnetoplumbite structure. Eu3+ fluorescence under dye‐laser excitation leads to the identification of two low symmetry (probably c2v) sites labeled A and B. Ab initio crystal field parameters for Eu3+ are calculated from the atomic coordinates deduced from the crystal stucture of LaMgAl11O19. These parameters and the experimental energy levels are used to derive an acceptable set of Bkq parameters for the A site. These Bkq corrected for the Nd3+/Eu3+ radial integrals ratio are used in turn to derive the Nd3+ Racah and spin‐orbit coupling parameters which fit the Nd3+ absorption spectrum at 4 K. At least two sets of parameters ‘‘high 2P1/2’’ and ‘‘low 2P1/2’’ are requi...