First-principles cluster methods were used to investigate vacancy-impurity complexes. A 1.682eV twelve-line optical band was attributed to a vacancy-Si complex which had a very unusual structure: with a Si atom at the center of a split vacancy. The method also accounted for the 1.945, 2.156 and 2.985eV optical transitions in trigonal vacancy-N defects.

J.P.Goss, R.Jones, S.J.Breuer, P.R.Briddon, S.Oberg: Physical Review Letters, 1996, 77[14], 3041-4