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International audience; The nitrogen-vacancy (NV) center in 3C-SiC, the analog of the NV center in diamond, has recently emerged as a solid-state qubit with competitive properties and significant technological advantages. Combining first-principles calculations and magnetic resonance spectroscopy we provide thorough insight in its magneto-optical properties. By applying resonantly excited electron paramagnetic resonance spectroscopy, we identified the zero-phonon absorption line of the 3 A 2 → 3 E transition at 1289 nm (within the telecom Oband) and measured its phonon sideband, the analysis of which reveals a Huang-Rhys factor of S = 2.85 and a Debye-Waller factor of 5.8 %. The low temperature spin-lattice relaxation time was found to be exceptionally long (T 1 = 17 s at 4 K). All these properties make NV in 3C-SiC a strong competitor for qubit application. In addition, the strong variation of the zero-field splitting in the range of 4K to 380K allows its application for nanoscale thermal sensing.

We present an X- and Q-band continuous wave (CW) and pulse electron paramagnetic resonance (EPR) study of a manganese doped [NH4][Zn(HCOO)3] hybrid framework, which exhibits a ferroelectric structural phase transition at 190 K. The CW EPR spectra obtained at different temperatures exhibit clear changes at the phase transition temperature. This suggests a successful substitution of the Zn2+ ions by the paramagnetic Mn2+ centers, which is further confirmed by the pulse EPR and 1H ENDOR experiments. Spectral simulations of the CW EPR spectra are used to obtain the temperature dependence of the Mn2+ zero-field splitting, which indicates a gradual deformation of the MnO6 octahedra indicating a continuous character of the transition. The determined data allow us to extract the critical exponent of the order parameter (β = 0.12), which suggests a quasi two-dimensional ordering in [NH4][Zn(HCOO)3]. The experimental EPR results are supported by the density functional theory calculations of the zero-field splitting parameters. Relaxation time measurements of the Mn2+ centers indicate that the longitudinal relaxation is mainly driven by the optical phonons, which correspond to the vibrations of the metal–oxygen octahedra. The temperature behavior of the transverse relaxation indicates a dynamic process in the ordered ferroelectric phase.

The metal–organic framework HKUST-1 is an attractive material for gas storage and gas separation applications because of its large surface area and high pore volume, and the presence of coordinatively unsaturated (cus) cupric ion sites. We investigated the interaction of alkenes and alkanes (ethene, 1-butene, ethane, and butane) with Cu2+ ions in their Zn-doped variant Cu2.97Zn0.03(btc)2 by continuous-wave electron paramagnetic resonance spectroscopy. Powder and single-crystal experiments revealed a characteristic change of cupric ion coordination from square planar to square pyramidal for the adsorption of ethylene and 1-butene and confirmed the formation of adsorption complexes at the cus sites of the Cu2+ ion in the mixed metal ion Cu–Zn paddle wheel (PW) units. Quantum chemical calculations based on density functional theory established a weak specific interaction between alkene π-orbitals and Cu2+ ions in a side-on coordination geometry. In contrast, no direct interaction between alkanes and the meta...

Whereas intrinsic defects in silicon carbide (SiC) have been widely considered for qubit applications, transition metals in this material have not yet been recognized as alternative systems. We have investigated the magneto-optical properties of the ${\mathrm{V}}^{3+}$ center in $4H\text{-SiC}$ by electron paramagnetic resonance (EPR) and photo-EPR spectroscopy in view of their possible application in quantum technology. We show that they fulfill all the requirements for such applications: a high-spin $S=1$ ground state, optically induced ground-state spin polarization of more than 70%, long spin-lattice relaxation times of the order of a second, as well as associated zero-phonon photoluminescence emission lines in the range of 1.8 \ensuremath{\mu}m. Further, the zero-field splitting parameter $D$ is temperature dependent and increases between $T=4\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and $T=292\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ linearly with a rate of 440 kHz/K, allowing potential nanoscale temperature sensing. These properties make the vanadium acceptor an extremely promising candidate for qubit applications with optical properties in the telecommunication optical range.

Structural characterization of metalloporphyrins in complex systems, such as native hydrocarbons, has been the focus of scientific and industrial interests for 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 radio frequency pulses at near the proton Larmor frequencies of 144 MHz to probe the paramagnetic vanadyls. By means of density functional theory calculations, ENDOR features are explained and ascribed to certain vanadyl porhyrin structural forms known to be present in crude oil.

Continuous wave X-band electron paramagnetic resonance (EPR) and density functional theory (DFT) were successfully applied to explore the incorporation and coordination state of the Cu2+ ions in the [Cd0.98Cu0.02(prz-trz-ia)] porous metal-organic frameworks. EPR measurements on powder samples and single crystals provided the full electron Zeeman g and copper hyperfine ACu interaction tensors including the orientation of their principal axes frames. DFT computations allowed for a detailed interpretation of the experimental results in terms of coordination symmetry and binding properties of the paramagnetic Cu2+ ions. Cupric ions were found to substitute Cd2+ ions in the dinuclear Cd-Cd units where they experience a noticeably distorted elongated pyramidal coordination environment formed by three nitrogen and two oxygen atoms from three linker molecules.

Atomlike defect levels in silicon carbide (SiC) polytypes have been proposed and proven to be an excellent platform for various quantum technology applications. Single-photon emitters, coherent control at room temperature, and temperature and magnetic field sensing at the nanoscale have already been demonstrated for the case of vacancy and divacancy defects in SiC and more recently proposed for negatively charged NV centers. NV centers, which allow a better control of their generation, offer in addition a further shift of the spectral range in the near infrared, i.e., in the $O$- and $S$-band telecom range. We demonstrate here that the association of high resolution optical spectroscopy and electron paramagnetic resonance spectroscopy combined with first-principles calculations allow the identification of the microscopic structure of the six distinct NV centers in $6H\ensuremath{-}\mathrm{SiC}$ and the assignment of their associated zero-phonon photoluminescence lines. Time resolved photo-EPR measurements at $T=4\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ show that NV centers in $6H\ensuremath{-}\mathrm{SiC}$ present spin lattice relaxation times of several seconds. These excellent qubit properties should enable their application and implementation in quantum information devices.

Mn-catalyzed oxidation of the Ashalcha heavy oil in porous media was examined. We used manganese(III) tris(acetylacetonate) as a convinient oil-soluble precatalyst that decomposes to catalytically active species during the temperature ramping. Reaction kinetics in the heavy oil oxidation with air indicated that the presence of the manganese ions changes the mechanism of the oxidation process, especially in the high-temperature region. To study precatalyst transformations in detail, we suggested the approach of combining X-ray powder diffraction (XRPD), thermal analysis, non-isothermal kinetic methods, and electron paramagnetic resonance (EPR). A comprehensive study of the decomposition of pure manganese(III) tris(acetylacetonate) and the subsequent comparison of its behavior to that in porous media in the presence of the oil allows us to shed light on some aspects of the mechanism of catalytic oxidation.

The effect of codoping of hydroxyapatite (HAP) nanocrystals with average sizes of 35 ± 15 nm during “wet” synthesis by CO 3 2− carbonate anions and Mn2+ cations on relaxation characteristics (for the times of electron spin–spin relaxation) of the NO 3 2− nitrate radical anion has been studied. By the example of HAP, it has been demonstrated that the electron paramagnetic resonance (EPR) is an efficient method for studying anion–cation (co)doping of nanoscale particles. It has been shown experimentally and by quantummechanical calculations that simultaneous introduction of several ions can be energetically more favorable than their separate inclusion. Possible codoping models have been proposed, and their energy parameters have been calculated.

The interplay between Mn ions and corrole ligands gives rise to complex scenarios regarding the metal centers' electronic properties expressing a range of high oxidation states and spin configurations. The resulting potential of Mn-corroles for applications such as catalysts or fuel cells has recently been demonstrated. However, despite being crucial for their functionality, the electronic structure of Mn-corroles is often hardly accessible with traditional techniques and thus is still under debate, especially under interfacial conditions. Here, we unravel the electronic ground state of the prototypical Mn-5,10,15-tris(pentafluorophenyl)corrole complex through X-ray spectroscopic investigations of ultrapure thin films and quantum chemical analysis. The theory-based interpretation of Mn photoemission and absorption fine structure spectra (3s and 2p and L2,3-edge, respectively) evidence a Mn(III) oxidation state with an S = 2 high-spin configuration. By referencing density functional theory calculations with the experiments, we lay the basis for extending our approach to the characterization of complex interfaces.

For high-spin centers, one of the key spectroscopic fingerprints is the zero-field splitting (ZFS) addressable by electron paramagnetic resonance. In this paper, an implementation of the spin-spin contribution to the ZFS tensor within the projector augmented-wave (PAW) formalism is reported. We use a single-determinant approach proposed by M. J. Rayson and P. R. Briddon [Phys. Rev. B 77, 035119 (2008)], and complete it by adding a PAW reconstruction term which has not been taken into account before. We benchmark the PAW approach against a well-established all-electron method for a series of diatomic radicals and defects in diamond and cubic silicon carbide. While for some of the defect centers the PAW reconstruction is found to be almost negligible, in agreement with the common assumption, we show that in general it significantly improves the calculated ZFS towards the all-electron results.

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., 6 pages, 3 Figures