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We report a systematic analysis of the crystal-field spectra of four fluoride compounds containing tetravalent actinide ions. The first part of this work [J. Chem. Phys. 95, 7194 (1991)] provided interpretation of the absorption spectra of UF4, NpF4, and PuF4. To extend our analysis to heavier elements of the series, low-temperature absorption spectra of AmF4 and CmF4, and site selective laser-induced emission and excitation spectra of Cm4+:CeF4 and Bk4+:CeF4 were obtained. A model energy level calculation was found to be in good agreement with the experimental results. It is shown that the crystal-field interaction in combination with spin–orbital coupling results in significant J mixing in the excited states, but ground state wave functions are still relatively pure in J character for the tetravalent actinide ions Am4+, Cm4+, and Bk4+. Trends in the parameters of the effective operator Hamiltonian are compared with those of a Hartree–Fock free-ion model. Interpretation of the ground-state splitting of the nominal S-state ion Bk4+ in CeF4 and color center formation in AmF4 are also discussed. [ABSTRACT FROM AUTHOR]

We report optical-spectroscopic studies of the ground-state splitting of the nominal S-state ion Cm3+ in LaCl3. A total splitting of 1.97±0.05 cm-1 for the 8S7/2 ground state of this system has been measured for the first time. Both electric and magnetic dipole transitions were observed. Energy levels of all four Kramers doublets of the 8S7/2 manifold were resolved by means of the site-selective excitation and emission spectra of 8S7/26D7/2 and 8S7/26P5/2 transitions. Our results show that the lowest component of the ground manifold is a μ=5/2 state dominated by M=|±7/2> in contrast to a previously reported μ=1/2 state. The crystal-field model, established through analyzing optical spectra of the excited states, predicts a ground-state splitting with the right ordering but greater magnitude. In comparison with the lanthanide S-state ion Gd3+, much stronger spin–orbit coupling and reduced electrostatic interaction in concert with greater crystal field interaction significantly influence the characteristics of the ground state of the actinide S-state ion. Contributions from within the 5f7 configuration account for most of the observed splitting. [ABSTRACT FROM AUTHOR]

An interpretation of the low-temperature absorption spectra of AnF4 (An=U, Np, Pu) is presented. Using an effective operator Hamiltonian with orthogonalized free-ion operators and initializing crystal-field parameter values based on a superposition model calculation for An4+ sites with C2 symmetry, good agreement between the model calculations and experimentally observed absorption band structure could be obtained. Correlations with published magnetic and heat capacity measurements are discussed. [ABSTRACT FROM AUTHOR]

The one-particle models of crystal-field theory provide a qualitative interpretation for the observed ground state splitting of four Kramers doublets of the [sup 8]S[sub 7/2] of Bk[sup 4+] doped into CeF[sub 4]. A set of nine nonzero (B[sub q][sup k]) parameters corresponding a C[sub 2v] point symmetry provide a very good correlation between the experimental data and simulated energy level schemes within a rms deviation of 13.7 cm-1. The calculated and experimental energy values have the same order-of-magnitude for the ground state and excited components. The total ground state splitting of the S-state ions of f-elements such as Bk[sup 4+] in CeF[sub 4] is larger when compared with Cm[sup 3+]:LaCl[sub 3] and Gd[sup 3+]:La(C[sub 2]H[sub 5]SO[sub 4])[sub 3]·9H[sub 2]O ions. The so-called crystal-field strength parameter, N[sub v], increases as a function of the increasing maximum splitting of the ground state due to a decrease in the participation of the pure [sup 8]S[sub 7/2] in the final composition of the ground state eigenvector. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The local environment of Cm[sup 3+] in a borosilicate glass has been probed by a combination of laser spectroscopy, structural modeling, and extended x-ray absorption fine structure (EXAFS) spectroscopy. The Stark splitting for the Cm f-f state transitions is significantly larger than the inhomogeneous line broadening that results from the disordered environment. As a result, the Cm optical spectrum can be fit using an effective operator Hamiltonian to obtain a set of crystal-field parameters. The fitting procedure, which requires the use of a descent-in-symmetry approach, provides a set of parameters for a best fit within tetragonal symmetry. These parameters are then linked to the local environment of Cm through exchange-charge modeling (ECM) of crystal field interactions. Cm in our borosilicate glass is best modeled with six oxygen ions with approximately tetragonal symmetry, and at an average distance of 2.31 (3) Å. The results of crystal-field modeling are supported by EXAFS results. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A method of analyzing inhomogeneous line broadening with crystal-field theory is presented. For actinide ions with unfilled f-shells in solids, the most important contribution to line broadening of f-electron transitions is from short-range interactions with distorted lattice. Optically active curium ions are used to measure the degree of radiation damage in the vicinity of their lattice site. The radiation damage was produced by decay of distant [sup 244]Cm[sup 3+] ions. Fluorescence line narrowing (FLN) spectra show that inhomogeneous line broadening induced by α-decay of the actinide ion [sup 244]Cm[sup 3+] in single crystals of LuPO[sub 4] and YPO[sub 4] has a microscopic nature. Namely, correlation is absent between energy levels of the Cm[sup 3+] ions at different local environments. Monte Carlo simulation of lattice distortion and crystal-field calculation of Cm[sup 3+] energy levels have been conducted to provide a quantitative interpretation of the experimental results. This method should be applicable to 4f- and 3d-ions in crystalline materials with lattice distortion. [ABSTRACT FROM AUTHOR]