Crystal field analysis and Monte Carlo simulation of lattice disordering for Cm[sup 3+] in YPO[sub 4] and LuPO[sub 4].

A method of analyzing inhomogeneous line broadening with crystal-field theory is presented. For actinide ions with unfilled f-shells in solids, the most important contribution to line broadening of f-electron transitions is from short-range interactions with distorted lattice. Optically active curium ions are used to measure the degree of radiation damage in the vicinity of their lattice site. The radiation damage was produced by decay of distant [sup 244]Cm[sup 3+] ions. Fluorescence line narrowing (FLN) spectra show that inhomogeneous line broadening induced by α-decay of the actinide ion [sup 244]Cm[sup 3+] in single crystals of LuPO[sub 4] and YPO[sub 4] has a microscopic nature. Namely, correlation is absent between energy levels of the Cm[sup 3+] ions at different local environments. Monte Carlo simulation of lattice distortion and crystal-field calculation of Cm[sup 3+] energy levels have been conducted to provide a quantitative interpretation of the experimental results. This method should be applicable to 4f- and 3d-ions in crystalline materials with lattice distortion. [ABSTRACT FROM AUTHOR]