Interpretation of the crystal-field parameters in a rare-earth substituted LiYF₄crystal

The crystal field in a LiYF 4 lattice is analysed in the framework of a superposition model and the results are compared with the findings in alkaline-earth fluorides and scheelites. Comments on the selection of coordinate systems (with respect to crystal axes) such that either of the imaginary crystal-field parameters could be ignored, or of approximating the S 4 symmetry by D 2d , are included.