  Optically active colour centres based on Nickel-Nitrogen impurities are
observed in natural diamond under continuous-wave excitation. The spectral
analysis shows that the single emitters have a narrow-band emission in the near
infrared, around 780 nm, which is almost entirely concentrated in the zero
phonon line even at room temperature. The colour centre excited-state lifetime
is as short as 2 ns, and the photoluminescence is linear polarized. These
striking features pave the way to the realization of a triggered single photon
source based on this colour centre emission well suited for open-air
single-photon Quantum Key Distribution operating in day-light conditions.
