Manifestation in IR-Luminescence of Cross Relaxation Processes between NV-Centers in Weak Magnetic Fields

The effect of a magnetic field on the luminescence from an ensemble of NV-centers in diamond was studied experimentally and theoretically. It was found that the intensity of infrared luminescence associated with transitions between singlet levels of NV-centers showed a pronounced increase in a near-zero magnetic field. The influence of the power and polarization of the laser radiation on the amplitude and shape of the revealed local maximum in the IR-luminescence of NV-centers was investigated. An eight-level photophysical model of an NV-center in the presence of an arbitrarily directed magnetic field was constructed and used as a basis to calculate the intensity of the luminescence emitted by an ensemble of NV-centers in both the visible and infrared spectral regions. It was shown that a phenomenological allowance for cross relaxation of NV-centers between each other and with other diamond paramagnetic centers within the framework of this model allows the experimentally observed fluorescence features of an ensemble of NV-centers in the presence of weak magnetic fields to be described.