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Coherent coupling of defect spins with surrounding nuclei along with the endowment to read out the latter, are basic requirements for an application in quantum technologies. We show that negatively charged boron vacancies (VB-) in electron-irradiated hexagonal boron nitride (hBN) meet these prerequisites. We demonstrate Hahn-echo coherence of the VB- electron spin with a characteristic decay time Tcoh = 15 us, close to the theoretically predicted limit of 18 us for spin defects in hBN. Modulation in the MHz range superimposed on the Hahn-echo decay curve are shown to be induced by coherent coupling of the VB- spin with the three nearest 14N nuclei through a nuclear quadrupole interaction of 2.11 MHz. Supporting DFT calculation confirm that the electron-nuclear coupling is confined to the defective layer. Our findings allow an in-depth understanding of the electron-nuclear interactions of the VB- defect in hBN and demonstrate its strong potential in quantum technologies.

Porous silica materials offer wide range of possibilities for enhancement of the productivity of oil reservoirs. However the mechanism of adsorption of polar components of crude oil on silica surface is poorly understood that hinders technological improvement of supports and oil extraction. We have synthesized opal films with the silica microspheres size of about 360 nm, specific surface area of 5.2 m2/g and pore size of 230 nm. We have fractionated and characterized oil and oil asphaltenes from heavy (Ashalchinskoe) oil. By pulsed electron paramagnetic resonance (EPR) and double electron nuclear resonance (ENDOR) in the W band frequency range (microwave frequency of 94 GHz, magnetic field of 3.4 T) we have studied the adsorption of oil asphaltenes on the surface of opal samples using the intrinsic for asphaltenes paramagnetic vanadylporphyrins (VO) complexes. 1H ENDOR spectra are found to be different for initial and the adsorbed samples in their central parts (that is a sign of asphaltenes VO disaggregation) whereas no significant changes in the W band EPR spectra were detected. Contrasting to alumina support, no strong electron proton interaction with the protons on the surface of SiO2 (presumably, silanol groups) was found and infiltration of the oiled opal films with gasoline changes the central part of 1H ENDOR spectra. It shows that the proton containing groups on the surface of amorphous SiO2 sample can significantly change the asphaltene adsorption properties and ENDOR of the intrinsic for oil paramagnetic centers could be used for the characterization of surface state in porous media in situ or operando., Comment: 7 pages, 5 figures, 43 references

The studies of chemical processes in spatially confined conditions are of interest from the fundamental and industrial points of view. By means of the W band EPR and 1H Mims electron nuclear double resonance (ENDOR) we show that the radiation-induced paramagnetic centers (E') in the synthetic nanoporous silica opals could be used as sensitive probes to investigate the surface modification and, potentially, reactions of polymerization in the confined by opal pores., Comment: 6 pages

Structural characterization of metalloporphyrins in complex systems such as native hydrocarbons is in the focus of scientific and industrial interests since many years. We describe electron-nuclear double resonance (ENDOR) of crude oil from the well without any additional sample treatment (i.e., in the native environment) in the magnetic field of about 3.4 T and temperature of 50 K by applying microwave pulses at 94 GHz (W-band) and radiofrequency pulses at near the proton Larmor frequencies of 144 MHz to probe the paramagnetic vanadyls. By means of density functional theory (DFT) calculations, ENDOR features are explained and ascribed to certain vanadyl porhyrin structural forms known to be present in crude oil., Comment: 20 pages including 4 Figures and Supporting Material with 1 Figure. Accepted for publication in ACS journal "Energy & Fuels"

Density functional theory based calculations within the framework of the plane-wave pseudopotential approach are carried out to define the phonon spectrum of hydroxyapatite Ca10(PO4)6(OH)2 (HAp). It allows to describe the temperature dependence of the electronic spin-lattice relaxation time T1e of the radiation-induced stable radical NO32- in HAp, which was measured in X-band (9 GHz, magnetic field strength of 0.34 T) in the temperature range T = (10-300) K. It is shown that the temperature behavior of T1e at T > 20 K can be fitted via two phonon Raman type processes with the Debye temperature of 280 K evaluated from the phonon spectrum., Comment: 6 pages, 3 Figures

Size-calibrated commercial nanodiamonds synthesized by high-pressure high-temperature (HPHT) technique were studied by high-frequency W and conventional X band electron paramagnetic resonance (EPR) spectroscopy. The numbers of spins in the studied samples were estimated. The core-shell model of the HPHT nanodiamonds was proposed to explain the observed dependence of the concentration of the N0 paramagnetic centers. Two other observed paramagnetic centers are attributed to the two types of structures in the nanodiamond shell., Comment: 8 pages

Synthesized by the wet chemical precipitation technique hydroxyapatite powders (HAp) with the sizes of the crystallites of (20-50) nm and 1000 nm 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 (by-products) could incorporate into the HAp structure. The concentration of the stable NO32- radicals detected after X-ray irradiation of the product at room temperature does not decrease even after annealing up to 400 oC. The relaxation times and EPR parameters of the axially symmetric NO32- paramagnetic centers are measured with high accuracy. Increased sensitivity and resolution of high-frequency EPR (95 GHz) allows to reveal additional paramagnetic centre(s) which origin is discussed. Analyses of electron-nuclear double resonance (ENDOR) spectra from 1H and 31P nuclei and ab-initio density functional theory (DFT) calculations allow suggesting that the paramagnetic centers and nitrate anions as the precursors of NO32- radicals preferably occupy PO43- site in the HAp structure., Comment: 10 pages, 5 figures