Fig. 9
PL spectrum of submicron powder D19 sample at T = 293 K (blue line) compared with that of its DP 0–0.05 polycrystalline precursor (red line) under the same conditions with laser excitation at λ = 488 nm (a), emission spectra, under 457 nm and 488 nm excitation, of two reference synthetic HPHT samples (size ~ 100 μm and < 150 nm) containing NVN centres (b) and the Raman spectrum of D19 sample recorded using the 457 nm excitation laser radiation (c). Arrows in (b): lines at 487.4 nm and 522 nm are single-phonon diamond Raman lines at 457 nm and 488 nm excitation, respectively, and the line at 504 nm is the ZPL of the NVN centres. In (b): dashed line—PL spectrum of D19 at λ = 488 nm excitation (for comparison). In (c): the diamond Raman line is centred at 1331.4 cm−1. δ = 7.3 cm−1 is a FWHM of diamond Raman line having the Lorentzian shape