The incorporation of Eu and Cm into the LaPO4 monazite structure is presented as a model phosphate system, relevant as a nuclear waste form. Site selective time resolved laser fluorescence spectroscopy of Eu and Cm was used as a structural probe. This revealed “satellite” species previously seen in LuPO4 [1]. These species are now clearly resolved and their origin is discussed. Apatite is considered to be a barrier to radionuclide migration due to its ability to incorporate a wide range of elements and the low solubility of actinides in phosphate media. Little is known about the incorporation mechanism of trivalent actinides and lanthanides in apatite at temperatures and conditions relevant to the environment. Previous work identifies Eu3+ incorporated into apatite at room temperature by TRLFS and describes the species as incorporated into the Ca(I) site with C3 symmetry. All published TRLFS emission spectra show a splitting of the F1 transition that is greater than expected for C3 symmetry and is attributed to impurities from natural apatite [2] or multiple site excitations [3]. The presented study eliminates these possibilities and produces similar spectra. The explanation proposed is that Eu3+ incorporates into amorphous grain boundaries producing a range of related species with low symmetry. Possibilities for charge compensation before and after heat treatment are also discussed [4, 5]. The mechanistic understanding of uptake in apatite is expanded to studies on biologically produced apatite. In this case, the mechanism proposed by the current study explains observed trends of uptake in apatite produced by Serratia bacteria. By tailoring the microstructure of the apatite produced one can design a material suited for various applications, such as filter material for decontaminating ground water or as a coating for surgical implants. These studies illustrate the value in attaining an atomic scale mechanistic understanding of the sorption and incorporation mechanisms that dictate actinide behavior. References [1] Murdoch, K.M., Edelstein, N.M., Boatner, L.A., Abraham, M.M.: Excited state absorption and fluorescence line narrowing studies of Cm3+ in LuPO4. J. Chem. Phys. 105, 2539 (1996). [2] M Gaft, R Reisfeld, G Panczer, G Boulon, S Shoval, B Champagnon, Optical Materials, 1997, 8, 149-156. [3] M Karbowiak, S Hubert, Journal of Alloys and Compounds, 2000, 302, 87-93. [4] R. Ternane, M. Trabelsi-Ayedi, N. Kbir-Ariguib, B. Pirou, Journal of Luminescence, 1999, 81, 165-170. [5] R. Sahoo, S.K. Bhattacharya, R. Debnath, Journal of solid state chemistry, 2003, 175, 218-225.
Kiel Holliday is a post doctoral scholar in the group of Thorsten Stumpf at the Institut für Nukleare Entsorgung at the Karlsruhe Institut für Technologie were he specializes in time resolved laser fluorescence spectroscopy and radionuclide migration. He received his Ph.D. in Radiochemistry from the University of Nevada, Las Vegas under Ken Czerwinski studying the synthesis, characterization and dissolution behavior of advanced nuclear fuel. Kiel Holliday has also performed investigations on materials for various applications such as waste forms, target materials, and exotic phase compositions for radiation damage studies.
