Spectroscopic studies of yellow nitrogen-doped CVD diamonds

• Removal brown color in CVD diamond by LPHT treatment.
• Generation of novel optical centers in CVD diamond by LPHT treatment
• Resonance Raman scattering in CVD diamond

Photoluminescence and absorption properties of commercial brownish yellow nitrogen-doped gem quality CVD diamonds have been characterized using imaging and spectroscopic techniques. The measurements have been performed on the diamonds in as-received state and after treatment with electron irradiation and high temperature (LPHT) annealing. It is found that single nitrogen defects in CVD diamond possess very high temperature stability, the positively charged single nitrogen atoms being exceptionally stable. In the as-received state, the diamonds show the signs of nitrogen aggregation, which are the result of the post-growth HPHT treatment. The treatment with electron irradiation and LPHT annealing has caused further aggregation of neutral nitrogen atoms and suppression (up to complete removal) of brown color. Many optical centers with narrow zero-phonon lines (ZPLs), not reported for natural diamonds, have been found all over the visible and near IR spectral ranges. Most of these centers are tentatively ascribed to Ni-related defects. A strong optical center with broad ZPL at a wavelength of 498.2 nm was excited with 325 nm laser. The effect of resonance Raman scattering on quasi-local vibrations of an optical center with ZPL multiplet at about 488 nm is reported.

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