A study was made of the T-line luminescence that was created by annealing at 400 to 600C. A shifting and splitting of the spectral features, upon substituting 13C and D isotopes, revealed the presence of two C atoms and one H atom in the center. Uniaxial stress and magnetic field measurements showed that the T center had monoclinic I symmetry and had an acceptor (-/0) level at 0.2eV below the conduction band. The use of  ab initio  cluster calculations led to a structure in which an interstitial C-H defect was bound to a substitutional C atom. The calculated vibrational modes were in good agreement with experimental data.

A.N.Safonov, E.C.Lightowlers, G.Davies, P.Leary, R.Jones, S.Oberg: Physical Review Letters, 1996, 77[23], 4812-5