It was found that the Yo line appeared in the photoluminescence and absorption spectra of n-type crystals after plastic deformation. The concept of the dislocation exciton was used to explain the results. The binding energy of the dislocation exciton was found to be equal to 0.027eV. It was suggested that dislocation excitons were destroyed by the dislocation charge and that the Yo line could therefore be related only to uncharged or slightly charged dislocations. It was also found that the edge of the absorption spectra of the deformed and undeformed crystals was significantly extended, as the result of a Franz-Keldysh effect that arose from charged dislocations. Stress birefringence was also observed in deformed crystals.

Y.G.Shreter, Y.T.Rebane, O.V.Klyavin, P.S.Aplin, C.J.Axon, W.T.Young, J.W.Steeds: Journal of Crystal Growth, 1996, 159, 883-8