  There is a continuous search for solid-state spin qubits operating at room
temperature with excitation in the IR communication bandwidth. Recently we have
introduced the photoelectric detection of magnetic resonance (PDMR) to read the
electron spin state of nitrogen-vacancy (NV) center in diamond, a technique
which is promising for applications in quantum information technology. By
measuring photoionization spectra on a diamond crystal we found two ionization
thresholds that were not reported before. On the same sample we also observed
absorption and photoluminescence signatures that were identified in literature
as Ni associated defects. We performed \emph{ab initio} calculation of the
photo-ionization cross-section of the nickel split vacancy complex (NiV) and
N-related defects in their relevant charge states and fitted the concentration
of these defects to the measured photocurrent spectrum, which led to a
surprising match between experimental and calculated spectra. This study
enabled to identify the two unknown ionization thresholds with the two acceptor
levels of NiV. Because the excitation of NiV is in infrared, the photocurrent
detected from the paramagnetic NiV color centers is a promising way towards
designing a novel type of electrically readout qubits.
