Field-induced mixing of states

Other significant spectral changes are also observed. The total splitting increases from 8.3 cm-1 at B=0 T to 24 cm-1 at 5= 12 T. Moreover, due to the field induced mixings of the wave functions, the radiative allowedness of the transitions from the T substates to the ground state is strongly redistributed. The emission from the lowest B-field disturbed substate 1(B) becomes dominant, while the transitions 11(B) —> 0 and III(B) — 0 lose intensity. This is also displayed in the emission decay time of substate I at 1.5 K, which becomes as short as 12 ps at 12 T, while it amounts to 85 ps at zero-field (see next section). Due to this B-field induced increase of radiative allowedness, it also becomes possible to tune magnetically other important properties like the mechanisms of vibrational deactivation [78-82]. 

Spectral determination of the field-induced mixing of zero-field states and a ground state population adjustment as a result of Zeeman splitting. 

In the simplest case of a donor-acceptor (D-A) molecule, the nonlinear optical activity arises from the electric-field-induced mixing of electronic states such as D-A and D+-A . This makes the response (polarizability) of the molecule different according to the sense of the electric field, and a second-order hyperpolarizability fi coefficient) is observed. If D and A are connected by some bridge, its role in promoting the electronic interaction will be quite similar to the bridge role in mixed-valence complexes. Metal complexes can play the role of donor or acceptor groups. Recent examples have been described with ferrocene or ruthenium(pentaammine) groups [48], but they are either monometallic or too short to be considered in this review. 

MCD spectroscopy combines the CD experiment with a longitudinal magnetic field, where the application of the magnetic field induces optical activity in any material so that all substances exhibit MCD activity. MCD probes the Zeeman splittings in the ground and excited states and the field-induced mixing between states. 

In table 13 we list the apphcations of MCPL to lanthanide systems that have been reported. Applications of this technique in sohds have focused on its use as a probe of Zeeman level degeneracy as a probe of site symmetry (Schwartz et al., 1977), or in studies interested in examining the field-induced mixing of electronic states as shown in recent apphcations of MCPL measurements from Tb(lll) and Ho(III) doped into garnets (Valiev et al., 2002a, 2002b). 

B-terms arise from field induced mixing of excited and ground states to other states with Zeeman interaction [10]. States with similar energy are prone to mix more. These transitions have absorption-band shape and are temperature independent. However, if the two mixed states are degenerate in energy, an A-term is observed. When the states are similar in energy then a derivative shaped signal is observed (pseudo A-term) [10]. 

Crystal field and exchange field induced mixing of the excited levels (/ = L ) into the ground state (/ = ) accounts successfully for the more complex magnetic properties of Sm " in some intermetallics (Buschow et al., 1973b Dublon et al., 1975). 

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