Effects of laser-induced heating on nitrogen-vacancy centers and single-nitrogen defects in diamond

We investigate the effects of laser-induced heating of NV- and P1 defects in diamonds by X-band CW EPR spectroscopy, with particular attention to temperature effects on the zero field splitting and electron polarization. A 532 nm laser with intensities of 7-36 mW is sufficient to heat diamond samples from room temperature to 313-372 K in our experimental setup. The temperature effects on the determined NV- zero-field splittings are consistent with previously observed non-optical heating experiments. Electron spin polarization of the NV- defects were observed to increase, then saturate, with increasing laser light intensities up to 36 mW after accounting for heating effects. We observe that EPR signal intensities from P1 centers do not follow a Boltzmann trend with laser-induced sample heating. These findings have bearing on the design of diamond-based polarization devices and magnetometry applications

Gauging the importance of structural parameters for hyperfine coupling constants in organic radicals

The identification of fundamental relationships between atomic configuration and electronic structure typically requires experimental empiricism or systematic theoretical studies. Here, we provide an alternative statistical approach to gauge the importance of structure parameters, i.e., bond lengths, bond angles, and dihedral angles, for hyperfine coupling constants in organic radicals. Hyperfine coupling constants describe electron–nuclear interactions defined by the electronic structure and are experimentally measurable, for example, by electron paramagnetic resonance spectroscopy. Importance quantifiers are computed with the machine learning algorithm neighborhood components analysis using molecular dynamics trajectory snapshots. Atomic–electronic structure relationships are visualized in matrices correlating structure parameters with coupling constants of all magnetic nuclei. Qualitatively, the results reproduce common hyperfine coupling models. Tools to use the presented procedure for other radicals/paramagnetic species or other atomic structure-dependent parameters are provided

NMR and EPR characterization of V2O5 as a cathode material for high-capacity Li-ion batteries

Li-ion batteries are the key technology for the electrification of the transport sector. Their enhancement requires fundamental understanding of the battery chemistry involving solid-state and interface reactions and processes. NMR and EPR were succesfully applied to investigate battery materials in many cases [1,2], however, mostly independent from each other. Here, both techniques are applied to investigate the cathode material V2O5. We exploit the strengths of EPR to target dilute surface defects and monitor redox reactions, and the strengths of NMR to identify phase transitions and the local surrounding of the nuclei under investigation