Relationships involving the interelectronic repulsion parameters, F-t (k = 2, 4, 6), the spin orbit coupling constant, zeta and J-mixing, with the D-5(0)-F-7(0) energy, E, have been investigated for Eu3+ using various approaches. First, the linear relationship between E and the F-7(1) splitting (or the second rank crystal field parameter) is shown to be applicable not only to glasses but also to solid-state crystalline systems with Eu3* site symmetry of C-2, C-2v, or lower. In these cases, the change in D-5(0)-F-7(0) energy is mainly due to the 1-mixing effect of F-7(1) = 2, 4, 6: most notably] = 2) which depresses F-7(0), whereas the D-3(0) energy is relatively constant. The 5D0-7F0 energy also depends upon certain energy parameters in the Hamiltonian, in particular, Ft and zeta(f). Model calculations show that increase in F-4 or F-6 produces an increase in E, whereas increase in F-2 produces a decrease in E. An increase in lambda(f) produces a decrease in E. These findings are rationalized. Most previous 4fs crystal field calculations have only considered the F and D terms of Eu3+ so that the Slater parameters are not well-determined. More reliable energy level data sets and crystal field calculations for Eu3+ with fluoride, oxide, or chloride ligands have been selected, and certain of these have been repeated since most previous calculations have errors in matrix elements. The fitted Slater parameters have been corrected for the effects of three-body Coulomb interactions. Some systems do not follow the ligand trend F similar to O > Cl for Slater and spin orbit parameters. From the limited data available, the average values of the corrected Slater parameters are greater for fluoride compared with chloride ligands, but the differences are comparable with the standard deviations of the parameters. There is no clear nephelauxetic series for these three types of ligands, with respect to spin orbit coupling. Previous correlations of E with various parameters are of limited value because the D-6(0)-F-7(0) energy difference not only depends upon the F-t and zeta(f) parameters but in addition is sensitive to the importance of J-mixing for low symmetry systems.