High temperature spectroscopy of ensembles of nitrogen-vacancy centers in diamond

We study the spectroscopy of an ensemble of negatively charged nitrogen-vacancy centers in diamond at high temperatures between room temperature and 700 K under high vacuum conditions. Spin resonances are studied using optical detection of magnetic resonance (ODMR), and optical spectroscopy is employed to study radiative transitions. Upon increasing the temperature, the intensity of radiative decay in visible and infrared decreased. In addition, the ODMR resonance frequencies were decreased, and the phonon line emission shifted to higher wavelengths. Density functional theory calculation of the zero-field splitting parameter (D) revealed that thermal expansion is not enough to explain the shift in the ODMR frequencies. Fitting the measured intensity of photo-luminescence with the theoretical predictions of the Mott-Seitz model yields the value of 0.22 eV for the energy barrier associated with nonradiative decay.