Positron annihilation and monochromatic illumination were used to determine the position, in the band-gap, of the negatively charged state of the monovacancy. The association of the 488nm absorption band (TH5) with divacancies was confirmed by positron annihilation, which also showed that the divacancy had a negative charge state in the band gap.

Negative Charging of Mono-and Divacancies in IIa Diamonds by Monochromatic Illumination. A.Pu, V.Avalos, S.Dannefaer: Diamond and Related Materials, 2001, 10[3-7], 585-7