Low-temperature photoluminescence (PL) spectroscopy was used to study electronic states associated with threading dislocations (Dlines) in strain-relaxedSi1−xGexlayers. The structures investigated were grown by ultrahigh vacuum chemical vapor deposition at 550 °C and consist of a Si(001) substrate, followed by a stepwise graded buffer layer, followed by a thick uniform compositionSi1−xGexlayer. The PL peak positions of the fourDlines after isochronal annealing at temperatures between 600 and 800 °C were measured. We show that the large energy shift of theD1line is due to a change in the local band gap energy at the dislocation core due to strain-driven diffusion of Ge atoms away from the dislocation core with an activation energyEa,which varies with Ge mole fractionx. ©1997 American Institute of Physics.