Optically addressable high-spin states (S ≥ 1) of defects in semiconductors are the basis for the development of solid-state quantum technologies. Recently, one such defect has been found in hexagonal boron nitride (hBN) and identified as a negatively charged boron vacancy (${\mathrm{V}}_{\mathrm{B}}^{-}$). To explore and utilize the properties of this defect, one needs to design a robust way for its creation in an hBN crystal. We investigate the possibility of creating ${\mathrm{V}}_{\mathrm{B}}^{-}$ centers in an hBN single crystal by means of irradiation with a high-energy (E = 2 MeV) electron flux. Optical excitation of the irradiated sample induces fluorescence in the near-infrared range together with the electron spin resonance (ESR) spectrum of the triplet centers with a zero-field splitting value of D = 3.6 GHz, manifesting an optically induced population inversion of the ground state spin sublevels. These observations are the signatures of the ${\mathrm{V}}_{\mathrm{B}}^{-}$ centers and demonstrate that electron irradiation can be reliably used to create these centers in hBN. Exploration of the ${\mathrm{V}}_{\mathrm{B}}^{-}$ spin resonance line shape allowed us to establish the source of the line broadening, which occurs due to the slight deviation in orientation of the two-dimensional B-N atomic plains being exactly parallel relative to each other. The results of the analysis of the broadening mechanism can be used for the crystalline quality control of the 2D materials, using the ${\mathrm{V}}_{\mathrm{B}}^{-}$ spin embedded in the hBN as a probe.

We discovered a family of uniaxially oriented silicon vacancy-related centers with $S=3/2$ in a rhombic $15R\text{−}\mathrm{SiC}$ crystalline matrix. We demonstrate that these centers exhibit unique characteristics such as optical spin alignment up to the temperatures of $250°\mathrm{C}$. Thus, the range of robust optically addressable vacancy-related spin centers is extended to the wide class of rhombic SiC polytypes. To use these centers for quantum applications it is essential to know their structure. Using high frequency electron nuclear double resonance, we show that the centers are formed by negatively charged silicon vacancies ${V_{\mathrm{Si}}}^{-}$ in the paramagnetic state with $S=3/2$ that is noncovalently bonded to the neutral carbon vacancy $V_{\mathrm{C}}^0$ in the nonparamagnetic state, located on the adjacent site along the SiC symmetry $c$ axis.

W-band pulsed EPR and ENDOR investigations of X-ray irradiated nanoparticles of synthetic hydroxyapatite Ca₉Pb(PO₄)₆(OH)₂ are performed. It is shown that in the investigated species lead ions probably replace the Ca(1) position in the hydroxyapatite structure.

Synthesized by the wet chemical precipitation technique, hydroxyapatite (HAp) powders with the sizes of the crystallites of 20–50 nm and 1 μm were analyzed by different analytical methods. By means of electron paramagnetic resonance (EPR) it is shown that during the synthesis process nitrate anions from the reagents (byproducts) could incorporate into the HAp structure. The relaxation times and EPR parameters of the stable axially symmetric NO 3 2− paramagnetic centers detected after X-ray irradiation are measured with high accuracy. Analyses of high-frequency (95 GHz) electron-nuclear double resonance spectra from 1H and 31P nuclei and ab initio density functional theory calculations allow suggesting that the paramagnetic centers and nitrate anions as the precursors of NO 3 2− radicals preferably occupy PO 4 3− site in the HAp structure.