Absorption Spectra of Lanthanide Complexes in Solution

The 4f electrons of lanthanides yield three types of transitions: (i) Internal 4f-4f transitions which give rise to sharp, narrow bands of comparatively weak intensities which are Laporte forbidden. (ii) Allowed 4fn−4fn-1 (n – l)d, which are relatively broad and intense. (iii) Broad and often intense 4fn−λ−1 fn+1 electron transfer bands generally occurring in the ultraviolet region (λ− represents a hole in the orbital concentratedmainly on the ligands).