Excitation and Emission Profiles of Cm(III) and Cm(IV) in Neat Samples and Lead Borosilicate Glasses
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Chemical and Analytical Sciences Division, Oak Ridge National Laboratory, P.O.Box 2008, Oak Ridge, TN 37831-6375, USA. 2 Dept. of Physical Sciences, Winston-Salem State University, Winston-Salem, NC 27110.
ABSTRACT We have been investigating the spectroscopy of actinides in materials having relevance to nuclear waste management. Discussed here are the excitation and emission profiles of curium in high temperature borosilicate glasses, and pure halide compounds. Probing the local coordination environment of Cm(III) in these matrices has been one of the goals of this study. Comparison of the nephelauxetic effects indicate that the silicate matrix provides a more basic environment than either F or Cl- surroundings found in pure compounds of curium. As a result, f - f transition energies are red shifted significantly in the silicate matrix as compared to that of the neat CmF3 system. Moreover, laser induced emissions have been noted with CmF 4 after treatment at elevated temperatures. The higher energy spectral region, consisting of emission bands at 20100 and 16750, is assignable to f- f transitions in Cm(III), which is the expected thermal decomposition product. Energy transfer from Cm(III), followed by a second photon absorption is believed to be responsible for the strong emission bands at 12550, and 13580 cm-'. from presently unidentified emitting species. Results are discussed in relation to the oxidation state and fluorescence dynamics of actinide species in neat compounds, as well as in matrices being considered for waste immobilization. INTRODUCTION Understanding the interaction between actinide species and immobilizing host materials is important for several reasons, which include modeling of their long term behavior and stability. Spectroscopic techniques provide vital fundamental information in such cases. Studies conducted on lanthanide systems [1] have shown that band positions and intensities of certain f f electronic transitions are comparatively sensitive to the metal coordination environment, and can provide valuable information on the interaction between the metal ion and its surroundings. Even though less data are available for actinide systems, comparable behavior is expected for them. It might be anticipated that the actinides would show larger "environmental" effects due 2 6 to the greater spatial extension of the 5f wave function, which is shielded less by the 6s 6p closed shells than for the analogous case with the lanthanides. When compared with other An(III) ions (An = actinide) Cm(III) is expected to show an enhanced radiative process. Its higher quantum efficiency is due to the large separation between the ground and first excited states, which reduces non-radiative quenching processes. As a result, fluorescence spectroscopy is a sensitive technique for probing curium in these matrices. In this paper a spectroscopic comparison is provided for Cm(III) in various media that include neat halide samples, borosilicate glasses and CaF2 matrices. The fundamental data described here provided
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