Nonradiative Transitions 3E → 1A1 and → 3A2 in the NV– Center in Diamond

A mechanism is proposed for a nonradiative transition between excited energy levels of the NV – center in diamond. The nonradiative transition between the levels of the spin triplet and the singlet is possible due to the spin–orbit interaction with simultaneous excitation of vibrational (vibronic) states of the cluster and the excitation of lattice phonons and, hence, can be obtained in the second order of perturbation theory. For describing this process, the spin–vibronic interaction operator and nonzero matrix elements ensuring nonradiative transitions are obtained. It is found that the matrix elements are proportional to the overlap integrals for one-particle electron wavefunctions. It is shown that the rate of transitions 3 E → 1 A 1 and → 3 A 2 are described by identical expressions. Therefore, the nonradiative transitions considered here are explained not by a multiphonon process, but by the excitation of vibronic states of atoms of the NV – center. Numerical estimates are in good agreement with experimental data.