T. Stumpf

Site-selective time-resolved laser fluorescence spectroscopy of Eu3+ in calcite.

Three samples of calcite homogeneously doped with Eu(3+) were synthesized in a mixed-flow reactor. By means of selective excitation of the 5D0-->7F0 transition at low temperatures (T<20 K), three different Eu(3+) species (species A, B, and C, respectively) could be discriminated. For each one, the emission spectrum and lifetime were obtained after selective excitation of the single species. On the basis of these data, species C could be identified as Eu(3+) incorporated into the calcite lattice on the (nearly) octahedral Ca(2+) site. Species B was also identified as Eu(3+) incorporated into the calcite lattice, but the ligand field shows a much weaker symmetry. Species A, however, is not incorporated into the crystals bulk, having 1-2 H(2)O ligands left in its first coordination sphere and showing very little symmetry, and is considered as Eu(3+) adsorbed onto the calcite surface. The emission spectra of species C for Eu:calcite grown in the presence of Na(+) were found to differ from those of Eu:calcite synthesized in the presence of K(+). The latter revealed a strong distortion in site symmetry, which was not observed in the samples grown in Na(+) solutions. This finding provides spectroscopic evidence in favor of an incorporation mechanism based on the charge-balanced coupled substitution of Na(+)+Eu(3+)<-->2Ca(2+).

Incorporation versus adsorption: substitution of Ca2+ by Eu3+ and Cm3+ in aragonite and gypsum.

The aim of the present work is to understand the interaction behaviour of trivalent f-elements with Ca2+-bearing mineral phases on a molecular level. This is achieved by use of time-resolved laser fluorescence spectroscopy (TRLFS) with Eu3+ and Cm3+ as atomic sensors on a trace concentration level. These ions are of special interest as models for trivalent actinides (e.g., Cm(III), Am(III) or Pu(III)) which strongly contribute to radiotoxicity in high level nuclear waste. Results from TRLFS with these trivalent ions show a significantly different mode of interaction in the two cases: while in aragonite only structural incorporation is observed, on gypsum nothing but inner-sphere surface complexes can be found. This shows how the anions forming the coordination sphere of the foreign ion control the formation of solid solutions as opposed to adsorption complexes.

Spectroscopic Identification of Ternary Cm−Carbonate Surface Complexes

The influence of dissolved CO(2) on the sorption of trivalent curium (Cm) on alumina (gamma-Al(2)O(3)) and kaolinite was investigated by time resolved laser fluorescence spectroscopy (TRLFS) using the optical properties of Cm as a local luminescent probe. Measurements were performed at T < 20 K on Cm loaded gamma-Al(2)O(3) and kaolinite wet pastes prepared in the absence and presence of carbonate in order to pictorially illustrate any changes through a direct comparison of spectra from both systems. The red-shift of excitation and emission spectra, as well as the increase of fluorescence lifetimes observed in the samples with carbonate, clearly showed the influence of carbonate and was fully consistent with the formation of Cm(III) surface species involving carbonate complexes. In addition, the biexponential decay behavior of the fluorescence lifetime indicated that at least two different Cm(III)-carbonate species exist at the mineral-water interface. These results provide the first spectroscopic evidence for the formation of ternary Cm(III)-carbonate surface complexes.

A new incorporation mechanism for trivalent actinides into bioapatite : a TRLFS and EXAFS study

One of the most toxic byproducts of nuclear power and weapons production is the transuranics, which have a high radiotoxicity and long biological half-life due to their tendency to accumulate in the skeletal system. This accumulation is inhomogeneous and has been associated with the chemical properties and structure of the bone material rather than its location or function. This suggests a chemical driving force to incorporation and requires an atomic scale mechanistic understanding of the incorporation process. Here we propose a new incorporation mechanism for trivalent actinides and lanthanides into synthetic and biologically produced hydroxyapatite. Time-resolved laser fluorescence spectroscopy and extended X-ray absorption fine structure have been used to demonstrate that trivalent actinides and lanthanides incorporate into the amorphous grain boundaries of apatite. This incorporation site can be used to explain patterns in uptake and distribution of radionuclides in the mammalian skeletal system.