The intense 738 nm narrow band luminescence of the SiV-centers for polycrystalline nanodiamonds produced by shock wave synthesis followed by grinding and separation into fractions with median sizes from 25 to 1000 nm are observed for all fractions. Polycrystals composed of tightly connected differently oriented diamond nanocrystals with mean sizes of 10-15 nm were formed by merging the boundary areas of the crystal lattices of adjacent nanocrystals. Size-dependent structural and luminescent properties were studied by comparative Raman and luminescence spectroscopy. Analysis of the Raman spectra from luminescent diamonds with median sizes from 1000 nm to 180 nm shows damage of the intergranular layers with the increase of amorphous carbon content. Raman spectroscopy for the fractions from 180 nm to 25 nm shows damage of the cubic diamond nanocrystals with the appearance of disordered carbon structures, which increases with decreasing median size accompanied with a strong decrease of the luminescent intensity. It was found than SiV luminescence intensity has a maximum at the median size of about 180 nm that is controlled by competition between deactivation of the SiV-centers by defects in the diamond nanocrystal lattice and nonradiative recombination centers in the volume of the intergranular layers.Keywords: Nanodiamonds, SiV-center
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