CROSS-RELAXATION DYNAMICS OF THE N-V CENTER IN DIAMOND AS STUDIED VIA OPTICALLY DETECTED MICROWAVE RECOVERY TRANSIENTS

The N-V center in diamond is a nitrogen-vacancy pair defect with an electronic triplet spin ground state. Upon optical excitation and in the presence of an applied magnetic field, two subensembles of N-V centers with different spin temperatures are created at liquid-helium temperatures. For certain magnetic fields, magnetically inequivalent N-V centers become resonant and the subensembles comprising these N-V centers tend to equilibrate due to cross relaxation. In this paper the dynamics of the cross-relaxation process is studied by means of optical-microwave double-resonance techniques. Pulsed microwave excitation of the ground-state spin transitions appears to produce a transient behavior of the optically induced fluorescence. A detailed kinetic analysis is given showing that the recovery rates obtained for a series of laser excitation powers, when extrapolated to zero excitation power, yield the cross-relaxation rate constant. The rate constant for cross relaxation among magnetically inequivalent N-V centers is found to be (2.0+/-0.3) X 10(2) s-1, whereas cross relaxation with doublet electron-spin species in the lattice occurs with a rate of (9.1+/-1.4) X 10(2) s-1.