Synthetic high-pressure high-temperature (HPHT) microdiamonds demonstrate strong resonant-like enhancement of the NV⁻ photoluminescence (PL) at unexpectedly low concentration of the substitutional nitrogen atoms (N_S) of 90 ppm, which is significantly smaller than the ∼250 ppm characteristic for conventional HPHT synthesis. The EPR, Raman, and luminescent spectroscopies, including time-resolved PL, provide evidence that this is due to competition between the increase in PL with increasing concentration of the NV⁻ centers and nonradiative deactivation of these centers by defects induced by the N_S in the diamond crystal lattice. It is suggested that the intensity of the NV⁻ center emission can be optimized by the appropriate choice of nitrogen doping concentration which does not substantially disrupt the diamond crystal lattice.

IR spectroscopy of fluorinated detonation nanodiamond demonstrates that an intense absorption band at ∼1344 cm^–1 and two smaller ones at ∼1324 and ∼1258 cm^–1 form the extended low wave-number wing of the observed consolidated spectrum in the range of 1100–1400 cm^–1. The intrinsic infrared absorption of CF_x bonding at the nanodiamond surface sites has been determined after subtraction of the contribution from remaining C–O and C–O–C groups inside the aggregates of tightly-bonded fundamental nanodiamond particles, which had not been subjected to fluorine attack and to their replacement by fluorine containing groups.