Anisotropies in the linear polarization of vacancy photoluminescence in   diamond induced by crystal rotations and strong magnetic fields
  We study the linear polarization properties of the photoluminescence of the neutral and negatively charged nitrogen vacancies and neutral vacancies in diamond crystals as function of their symmetry and their response to strong external magnetic fields. The linear polarization degree, which exceeds 10% at room temperature, and rotation of the polarization plane of their zero-phonon lines significantly depend on the crystal rotation around specific axes demonstrating anisotropic angular evolutions. The sign of the polarization plane rotation is changed periodically through the crystal rotation, which indicates a switching between electron excited states of orthogonal linear polarizations. At external magnetic fields of up to 10 T, the angular dependences of the linear polarization degree experience a remarkable phase shift. Moreover, the rotation of the linear polarization plane increases linearly with rising magnetic field at 6 K and room temperature, for the negatively charged nitrogen vacancies, which is attributed to magneto-optical Faraday rotation. 
D. Braukmann, V. P. Popov, E. R. Glaser, T. A. Kennedy, M. Bayer, and   J. Debus
cond-mat.mes-hall