Photo-ionization of the nitrogen-vacancy center in diamond

In this paper it is shown that the [N-V]− center in diamond is not photochemically stable. With intense excitation a proportion of the [N-V]− centers in a crystal are converted to [N-V]0 centers. Two ionization processes are identified. One occurs when the center is directly excited to the first excited state. The other process is indirect and occurs when there is photo-ionization of the accompanying substitutional nitrogen centers in the crystal. The dynamics and the wavelength dependence of these processes are measured and interpreted.