I was looking at this question:
And got some answers that answered some of the questions I had, but not all. I am still trying to conceptually grasp why f-f transitions happen at all because a) there should be no crystal field splitting because of the lanthanide contraction (orbitals are closer to the nucleus, are not perturbed by the ligand sphere as there is next to no interaction) and b) then all f-electrons should be degenerate.
This is in contrast to d-elements, where d-d interactions can be explained by crystal field splitting and, more precisely, by looking at Tanabe-Sugano-diagrams (because not every d-d transition is the same due to the symmetry of the orbitals involved and spin-orbit-coupling).
So how to best explain this?
I am asking because I was confused by this diagram:
In this diagram, one excited Eu(III) state of 5D(0) can decay to 7F(6) state. Is this a d-f transition or a f-f transition?
Sorry if this is obvious, but even though the term symbol is a D, this not always coincides with the orbital; for example, Sm(III) has the ground state term symbol 6H(5/2), but obviously the outer electrons don't reside in a "h-orbital".