Bulletin des societes chimiques belges vol:106 issue:11 pages:685-689
The magnetic dipole transition 5D1 <-- 7F0 of Eu3+ can be used as a sign reference transition in the magnetic circular dichroism (MCD) spectrum. The corresponding MCD signal is always a positive pseudo A-term, regardless the point symmetry of the europium site. Left circular polarized light (l.c.p.) is absorbed to the upper Zeeman level in the 5D1 manifold and right circularly polarized light (r.c.p.) to the lower Zeeman component. Since an MCD spectrum expresses Delta epsilon = epsilon(l.c.p.) - epsilon(r.c.p.) (epsilon is the molar absorptivity) in function of the wavenumber, the pseudo A-term can be seen as a superposition of a positive lobe corresponding to the absorption of l.c.p. and a negative lobe corresponding to the absorption of r.c.p.. Although for many Eu3+ systems the areas of the positive and the negative lobe are equal, some Eu3+ systems show an asymmetrical pseudo A-term. Examples are europium doped fluorozirconate and fluorophosphate glass. A theoretical explanation is given for the asymmetry of the MCD signal of the 5D1 <-- 7F0 transition in randomly-oriented systems such as solutions and glasses. The fine structure of the pseudo A-term can related to the magnitude of the crystal-field splitting of the 5D1 manifold and to the sign of the B-0(2) field parameter.