It was pointed out that thermal annealing could destroy the di-carbon center, with its zero-phonon line at 0.969eV (7818/cm). Following the destruction of the di-carbon center, many previously unreported photoluminescence lines were observed. The point defects which gave rise to these lines consisted of C and O atoms. It was also noted that the annealing of the di-carbon center was not completely understood. The break-up process was not the only means by which to destroy the di-carbon center, and the presence of other defects in the crystal could affect the annealing process.

T.K.Kwok: Physical Review B, 1995, 51[23], 17188-91