VIBRONIC COUPLING MODEL FOR THE INTENSITIES OF f-f TRANSITIONS IN OCTAHEDRAL LANTHANIDE (III) COMPLEXES

Abstract

A general theory of vibronically induced electric-dipole intensity in the f-f transitions of octahedral $(O_{h})$ six-coordinate trivalent lanthanide ion complexes is presented. The theory includes both static (point charge crystal field) and dynamic (transient ligand dipoles) coupling between the metal ion and the ligands. Electronic dipole intensity is introduced into the vibronic components of the parity-forbidden $Ln^{3+}$ f-f transitions via vibronic coupling between the chromophoric 4f-electrons and the $\nu_{3}(t_{1u}), \nu_{4}(t_{1u})$ and $\nu_{6}(t_{2u})$ skeletal vibrational modes of the Octahedral $LnL_{6}$ system. Calculations based on the theoretical model are presented for the $^{7}F_{0}\rightarrow\ ^{5}D_{1},^{7}F_{0}\rightarrow\ ^{5}D_{2}$ and $^{7}F_{1}\rightarrow\ ^{5}D_{1}$ transitions of the $EuCl^{3-}_{6}$ complex, and the results are compared with experimental data reported for $Cs_{2}NaEuCl_{6}$.