Behavior-type method for polarized Raman spectra of defects in cubic crystals

The intensity of polarized-light Raman scattering from a localized vibration of a point defect in a crystal is a discrete average over all the possible orientations of the defect. Much of the information contained in the Raman tensor of the vibrational mode is hidden by this discrete averaging. Partial or complete preferential reorientation or destruction of the defect, achieved by a so-called orientating operator $\hat{F}$, alters this average and permits in principle a determination of the symmetry of the defect, the nature of the modes, and the relative values of the elements of the Raman tensor. A discussion based on group theory is given for all of the possible symmetries of a point defect in a cubic lattice, as well as for all the possible symmetries of the orientating operator $\hat{F}$. The concept of behavior type of the Raman intensity parameters is introduced, which plays a central role in the application of the theory because it permits an efficient analysis of the data. The results are summarized in a series of tables. These are also helpful in choosing a suitable symmetry of the preferential orientating operator $\hat{F}$ (often from a polarized-light bleaching) and the suitable Raman polarization geometries. Similar methods can be applied to other host symmetries, and also to the study of the influence of an applied external field, e.g., an electric or stress field.