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Video abstract for the article 'Photo-induced ionization dynamics of the nitrogen vacancy defect in diamond investigated by single-shot charge state detection ' by N Aslam, G Waldherr, P Neumann, F Jelezko and J Wrachtrup (N Aslam et al 2013 New J. Phys. 15 013064). Read the full article in New Journal of Physics at http://iopscience.iop.org/1367-2630/15/1/013064/article. GENERAL SCIENTIFIC SUMMARY Introduction and background. The nitrogen--vacancy (NV) defect centre in diamond is a single photon emitter that is associated with an electron and a few nuclear spins. The spin states can be initialized and read out optically on the single level. The long coherence lifetimes of these spin states enable the use of NV centres for instance as magnetic and electric field sensors under ambient conditions. Furthermore their potential as quantum bits has been demonstrated in the recent years. The NV defect mainly occurs in two different charge states: the negative and the neutral one. It is the negatively charged NV defect that is used for all mentioned applications. In this work the optically induced dynamics between the two charge states is examined with different methods and with emphasis on its dependence on excitation wavelength and power. Main results. One of the main results is the experimental proof that a recently observed 'dark' state of the NV defect is indeed its neutral charge state. Upon illumination, continuous ionization and recombination processes occurr. The rates of these processes depend on the excitation wavelength and power. The optimum wavelengths to gain maximum NV minus population were determined. Additionally, the transition from one-photon ionization to two-photon ionization was observed by varying the excitation laser light from the blue to the green spectrum. This change in the ionization process revealed the energy level of the ground state of NV minus within the bandgap of diamond. Wider implications. This work has revealed many new insights into the photophysics of NV defects. With its detailed study of switching behaviour between the two charge states it has provided the recipes for implementing methods like Photoactivation Localization Microscopy (PALM) or Stochastic Optical Reconstruction Microscopy (STORM) with NV centres which enables us to resolve single NV's below the sub-diffraction limited area. Additionally high fidelity charge and spin state initialization can now be performed which is crucial for quantum information applications but also for quantum metrology.