N. Magnani

Superposition-model analysis of rare-earth doped BaY 2 F 8

The energy level schemes of four rare-earth dopants (Ce 3+ , Nd 3+ , Dy 3+ , and Er 3+ ) in BaY 2 F 8 , as determined by optical absorption spectra, were fitted with a single-ion Hamiltonian and analysed within Newmans Superposition Model for the crystal field. A unified picture for the four dopants was obtained, by assuming a distortion of the F m ligand cage around the RE site; within the framework of the Superposition Model, this distortion is found to have a marked anisotropic behaviour for heavy rare earths, while it turns into an isotropic expansion of the nearest-neighbours polyhedron for light rare earths. It is also inferred that the substituting ion may occupy an off-center position with respect to the original Y 3+ site in the crystal.

S mixing and quantum tunneling of the magnetization in molecular nanomagnets.

The role of S mixing in the quantum tunneling of the magnetization in nanomagnets has been investigated. We show that the effect on the tunneling frequency is huge and that the discrepancy (more than 3 orders of magnitude in the tunneling frequency) between spectroscopic and relaxation measurements in Fe(8) can be resolved if S mixing is taken into account.

Optical spectroscopy of SrWO4 : Nd3+ single crystals

The optical properties of SrWO4 crystals doped with Nd3+ have been investigated at temperatures ranging from 10 to 300 K. The scheme of the energy levels up to 20 000 cm−1 has been deduced from low temperature measurements and reproduced by theoretical calculations based on a parametric Hamiltonian including Coulombic, spin–orbit and crystal field terms. The spontaneous transition probabilities, the branching ratios and the radiative lifetime have been calculated in the framework of the Judd–Ofelt theory and compared with the experimental results for the 4F3/2 emitting level. The optical bands are broadened because of crystal field inhomogeneities caused by charge compensation processes accompanying the substitution of Nd3+ for Sr2+. This fact and the high emission cross section values obtained for the emission from the 4F3/2 multiplet indicate Nd:SrWO4 as a possible active medium for tunable laser operation.

Optical spectroscopy and crystal-field analysis of YAl3 (BO3)4 single crystals doped with dysprosium

YAl3 (BO3)4 crystals doped with Dy3+ were grown from a potassium trimolybdate flux. Their absorption and visible emission spectra and decay curves were measured at temperatures ranging from 10 to 298 K. The complete energy level scheme has been deduced from the low temperature measurements and reproduced by theoretical calculations based on a parametric Hamiltonian including coulombic, spin–orbit and crystal-field terms. The Judd–Ofelt parametrization scheme has been applied to the analysis of the room temperature absorption spectra. The calculated radiative lifetime of the 4F 9/2 state is 344 μs; this value is reasonably consistent with the experimental data.

Spectroscopic investigation and crystal field modelling of Dy3+ and Er3+ energy levels in yttrium aluminium borate (YAB) single crystals

High resolution (0.04 cm−1) absorption spectra of Dy3+-doped YAl3(BO3)4 (YAB) single crystals were measured by Fourier transform spectroscopy in the spectral (2000–23 000 cm−1) and temperature (9–300 K) ranges. Samples with nominal 1 and 4% Dy/Y molar ratios were studied. Dy3+ transitions from the 6H15/2 ground state to the 6H13/2, 6H11/2, 6H9/2+ 6F11/2, 6H7/2+ 6F9/2, 6H5/2, 6F7/2, 6F5/2, 6F3/2, and 4F9/2 excited states were analysed. A small (~3.3 cm−1) splitting between the first two sublevels of the 6H15/2 ground manifold was detected. The experimentally determined energy levels were fitted with a single-ion Hamiltonian and the crystal-field parameters were obtained. The same procedure was applied to analyse the previously published high resolution spectra of YAB:Er3+, leading to a reliable unified picture for the two dopants.

Perturbative approach to J mixing in f -electron systems: Application to actinide dioxides

We present a perturbative model for crystal-field calculations, which keeps into account the possible mixing of states labelled by different quantum number

Microscopic theory of the insulating electronic ground states of the actinide dioxides AnO2 (An =U, Np, Pu, Am, and Cm)

J

X-ray Diffraction, Mössbauer Spectroscopy, Magnetic Susceptibility, and Specific Heat Investigations of Na4NpO5 and Na5NpO6.

. Analytical

Macroscopic evidence of quantum coherent oscillations of the total spin in the Mn-[

J

\mathsf{3\times3}

-mixing results are obtained for a Hamiltonian of cubic symmetry and used to interpret published experimental data for actinide dioxides. A unified picture for all the considered compounds is proposed by taking into account the scaling properties of the crystal-field potential.