Studies of local structure of Cm3+ in borosilicate glass using laser and x-ray spectroscopic methods and computational modeling

The local environment of Cm3+ 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 li ne broadening that results from the disordered environment. As a result, th e Cm optical spectrum can be fit using an effective operator Hamiltonian to obtain a set of crystal-field parameters. The fitting procedure, which req uires the use of a descent-in-symmetry approach, provides a set of paramete rs for a best fit within tetragonal symmetry. These parameters are then lin ked to the local environment of Cm through exchange-charge modeling (ECM) o f crystal field interactions. Cm in our borosilicate glass is best modeled with six oxygen ions with approximately tetragonal symmetry, and at an aver age distance of 2.31 (3) Angstrom. The results of crystal-field modeling ar e supported by EXAFS results. (C) 2000 American Institute of Physics. [S002 1-9606(00)71002-6].