Optical properties of the Cm3+ ion in single crystals

The Cm3+ ion, atomic number 96, has the electronic configuration and is the actinide analog of the lanthanide ion Gd3+. The ground term has only approximately 87 percent 8S7/2 parentage due to the large spin-orbit interaction as compared to the almost 100 percent 8S7/2 parentage for Gd3+. The electrostatic interaction between equivalent electrons in the f7 shell results in a large gap between the octet state of the ground term and the sextet states of the excited multiplets. For Gd3+ this splitting results in a gap greater than 30,000 cm-1. The greater spatial extent of the 5f electron shell results in a smaller electrostatic interaction between equivalent electrons in the 5f shell than in the 4f shell. Thus for Cm3+, this splitting is on the order of 16,000 cm-1. The ground term multiplet splitting is small, because the largest component of the ground multiplet has zero angular momentum. However for Gd3+ in most crystals, this ground term splitting is much less than approximately 1 cm-1. Early detailed studies of the Cm3+ optical spectra were performed with the 244Cm isotope. During the past decade or so, multi-milligram quantities of 248Cm have become available. A number of single crystals have been doped with the 248Cm isotope and optical studies of these samples have been performed using laser selective excitation and fluorescence techniques. Excited state absorption studies allowed the collected of data to 40,000 cm-1 using two visible lasers. Results from these experiments will be reviewed and comparisons will be made between the 5f and 4f series.