Photoluminescence excitation spectroscopy of N vacancy centers in type Ib diamond nanocrystals shows that in spite of spectral diffusion and spin-nonconserving transitions, zero-phonon line-width as small as 16MHz, which was nearly lifetime limited, could be observed at low temperature. Relatively small effects of spectral diffusion have also been observed in a small fraction of N-vacancy centers.

Zero-Phonon Linewidth of Single Nitrogen Vacancy Centers in Diamond Nanocrystals. Y.Shen, T.M.Sweeney, H.Wang: Physical Review B, 2008, 77[3], 033201 (3pp)