It was recalled that, in a crystal which was deformed by slip, the tensors which characterized the elastic field behind all moving dislocations were of the same form. If the dislocations interacted with low-symmetry point defects, the latter were aligned in the same direction and this led to an anisotropy of the macroscopic properties of the crystal. The point centers retained their properties when the dislocations moved away, while the orientation of the centers changed. New experimental data on F2 centers in LiF were obtained here which confirmed the effect. It was suggested that the latter was of general occurrence and involved a new type of point defect ordering by plastic deformation. This ordering reduced the macroscopic symmetry of the crystal. It was proposed that color centers were not the only defects to be involved in such an interaction, but the fact that such centers exhibited optical transitions with optical dipole moments that were related to the orientation of the cluster made the effect especially noticeable. The clearest manifestation of the effect was observed when oriented point defects were produced by dislocations, as in the case of the Nc center. In this case, all of the centers which were produced were oriented. The presence of a large number of centers in the bulk before deformation did not negate the effect but concealed it; because only a small fraction of the centers was located near to moving dislocations, while the other defects were randomly oriented.

A.N.Stepanov, A.V.Kornilov: Kristallografiya, 1994, 39[4], 693-5 (Crystallography Reports, 1994, 39[4], 625-7)