Optical properties of vacancies in diamond at high magnetic fields

Abstract

Polarization resolved photoluminescence spectroscopy measurements are performed on defect centers in diamond. The photoluminescence of the negatively charged as well as the neutral nitrogen vacancy center shows remarkable linear polarization degrees of about 20 % at room temperature. The anisotropic angular dependence of the linear polarization characteristics mirrors the crystallographic symmetry of the defect center. In contrast to the linear polarization, the circular polarization properties of the defect centers are rather weak due to the small orbital g-factors of the defect center electrons. The latter were measured via the Zeeman splitting of the defect center's zero-phonon lines, which also allows to define the symmetry and energetic ordering of the defect center energy levels. A Fano resonance in the energy of the nitrogen vacancy center zero-phonon lines is observed via photoluminescence-excitation spectroscopy. This resonance is accompanied by a charge transfer between the two charge states of the nitrogen vacancy center which leads to an increase in the photoluminescence intensity of up to a factor of 30. It is shown that this recharging process is more important in diamonds with low nitrogen vacancy center concentration, while in diamonds with high concentration the recharging occurs via nitrogen impurities, which act as electron donors. In addition, optical detection of magnetic resonances via application of microwaves with powers in the range of only a few nanowatts demonstrates the high sensitivity of the negatively charged nitrogen vacancy center to microwave radiation. Moreover, microwave amplification at nitrogen impurities might viably have been observed in the diamond crystal, which could make the diamond a possible candidate for a solid state maser that operates at room temperature.