Spin properties of defects in carbon nanostructures are one of the
fundamental directions in the physics of nanomaterials. The problem of doping
nanostructures and creating intrinsic and extrinsic defects in such structures as a result
of various actions (heat treatment, ionizing radiation, chemical action, etc.) is playing
the central role in the further implementation of these nanostructures in real devices.
Electron paramagnetic resonance (EPR) is known to be one of the most informative
methods to study the intrinsic and extrinsic defects at the molecular level. The use of
different frequency bands (low frequency X-band or high frequency W-band) and
different regimes of the EPR signal detection (continuous or pulsed) allows one to get
an access not only to the identification an electronic and microscopic structure of the
defects in the crystalline matrix, but also to study coherence properties of the defects'
spin. In this chapter, by means of EPR, we provide the direct observation of
paramagnetic impurities in the crystalline core of nanodiamonds and we also show that
nitrogen impurities in nanodiamonds interact with the diamond lattice in a similar way
as in the bulk diamond crystals. We also present the results of observation of highdensity
NV defect ensembles created directly by high-pressure high-temperature
(HPHT) sintering procedure of the detonation nanodiamonds and show that the spin
ensemble of the NV defects is characterized by the long spin-lattice and spin-spin
relaxation times. The latter is important for bioimaging and quantum sensing
applications.
Keywords: Angular dependence, Detonation nanodiamonds, EPR, Electron spin
echo (ESE), ESE detected EPR, Euler angles, Fine structure, High-frequency
EPR, EPR spectra simulation, HPHT nanodiamonds, Hyperfine interaction, Multifrequency EPR, Natural diamond nanocrystals, Nitrogen centers, Nitrogen pairs,
NV centers, Spin Hamiltonian, Size effect, Symmetry, Synthetic nanodiamonds.
