A dislocation exciton line was detected in the photoluminescence and absorption spectra of crystals after plastic deformation. The binding energy of the dislocation exciton was estimated to be 0.027eV. It was suggested that the exciton line was related to uncharged or slightly charged dislocations. The type of dislocation which was responsible for the line remained unknown since, although the experiments revealed the presence of a considerable number of small loops, it was not certain that they were the result of deformation, and might have been the result of electron radiation damage. It was also found that the edges of the absorption spectra of the deformed and non-deformed crystals were appreciably extended. This was tentatively attributed to a Franz-Keldysh effect that arose from charged dislocations. Transmission electron microscopy showed that dislocations with a large edge component predominated; with some dislocations being of 60 type. It was not possible to attribute the exciton line to 60 dislocations, or to 90 partial dislocations of the 60 dislocations. This was because no correlation could be found between the slip planes and the spatial distribution of the intensity of the exciton line. Mapping of polycrystalline samples had showed that this line was most intense in tangles of highly irregular convoluted dislocations. Also, most of the dislocations (excluding screw and Frank types) were inherently charged; due to the ionicity of the crystal. Because the high electric fields of the dislocations were able to destroy the excitons, it was assumed that small Frank loops (which could form as a result of the condensation of point defects that arose during deformation) might be responsible for the exciton line. It was not found to be possible to exclude the possibility that some of the charged 60 dislocations might be neutralized by impurities, so as to make a contribution to absorption and luminescence.

J.G.Shreter, Y.T.Rebane, O.V.Klyavin, P.S.Aplin, C.J.Axon, W.T.Young, J.W.Steeds: Solid State Phenomena, 1996, 51-52, 93-8