  Nanodiamond crystals containing single color centers have been grown by
chemical vapor deposition (CVD). The fluorescence from individual crystallites
was directly correlated with crystallite size using a combined atomic force and
scanning confocal fluorescence microscope. Under the conditions employed, the
optimal size for single optically active nitrogen-vacancy (NV) center
incorporation was measured to be 60 to 70 nm. The findings highlight a strong
dependence of NV incorporation on crystal size, particularly with crystals less
than 50 nm in size.
