Cross-relaxation dynamics of optically excitedN-Vcenters in diamond

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Abstract
Upon the cw optical excitation of N-V centers in diamond, a spin alignment in the ensemble of nonexcited N-V defects in the electron spin-triplet ground state is induced. When the diamond sample is subjected to magnetic fields of suitable directions and strengths, cross relaxation (CR) and level anticrossing are found to affect the ground-state spin alignment as well as the intensity of the emission due to the photoexcited N-V centers. In this paper, a study of the dynamics involved in the cross-relaxation and autocrossing processes is reported, utilizing techniques for the optical detection of spin-coherent transients. A major finding is that when CR conditions prevail, the stimulated spin-echo and spin-locking signals decay at a rate about three times faster than in the situation in which CR does not occur. The results are accounted for by considering the magnetic dipole-dipole interactions within the ensemble of N-V centers in the triplet ground state in a memory function approach.