Part the Raman spectrum of a single crystal of terbium aluminium garnet was studied using various exciting frequencies. A strong electronic peak corresponding to a transition within the 7F6 manifold was observed at 84 cm^-1. The dependence of the electronic peak intensity on exciting frequency was investigated by comparison with the phonon modes at 139 cm^-1 and 266.8 cm^-1, the latter being used as internal standards. Intensity ratios were thus calculated and interpreted on the basis of a modified version of Placzek's polarizability model.
These measurements showed a resonance enhancement of the electronic Raman transition as the incident radiation frequency approached the frequency of absorption, that is, there was a definite pre-resonance Raman effect involved.