Shining light on diamond particles makes them MRI-“bright,” opening avenues for room temperature hyperpolarized liquids.

The nitrogen-vacancy (NV) centre in diamond is emerging as a promising platform for solid-state quantum information processing and nanoscale metrology. Of interest in these applications is the manipulation of the NV charge, which can be attained by optical excitation. Here, we use two-colour optical microscopy to investigate the dynamics of NV photo-ionization, charge diffusion and trapping in type-1b diamond. We combine fixed-point laser excitation and scanning fluorescence imaging to locally alter the concentration of negatively charged NVs, and to subsequently probe the corresponding redistribution of charge. We uncover the formation of spatial patterns of trapped charge, which we qualitatively reproduce via a model of the interplay between photo-excited carriers and atomic defects. Further, by using the NV as a probe, we map the relative fraction of positively charged nitrogen on localized optical excitation. These observations may prove important to transporting quantum information between NVs or to developing three-dimensional, charge-based memories.

One of the most remarkable properties of the nitrogen-vacancy (NV) center in diamond is that optical illumination initializes its electronic spin almost completely, a feature that can be exploited to polarize other spin species in their proximity. Here we use field-cycled nuclear magnetic resonance (NMR) to investigate the mechanisms of spin polarization transfer from NVs to 13 C spins in diamond at room temperature. We focus on the dynamics near 51 mT, where a fortuitous combination of energy matching conditions between electron and nuclear spin levels gives rise to alternative polarization transfer channels. By monitoring the 13 C spin polarization as a function of the applied magnetic field, we show 13 C spin pumping takes place via a multi-spin cross relaxation process involving the NVspin and the electronic and nuclear spins of neighboring P1 centers. Further, we find that this mechanism is insensitive to the crystal orientation relative to the magnetic field, although the absolute level of 13 C polarization ⎯ reaching up to ~3% under optimal conditions ⎯ can vary substantially depending on the interplay between optical pumping efficiency, photo-generated carriers, and laser-induced heating.

We report on the use of optical Faraday rotation to monitor the nuclear-spin signal in a set of model (19)F- and (1)H-rich fluids. Our approach integrates optical detection with high-field, pulsed NMR so as to record the time-resolved evolution of nuclear-spins after rf excitation. Comparison of chemical-shift-resolved resonances allows us to set order-of-magnitude constrains on the relative amplitudes of hyperfine coupling constants for different bonding geometries. When evaluated against coil induction, the present detection modality suffers from poorer sensitivity, but improvement could be attained via multipass schemes. Because illumination is off-resonant i.e., the medium is optically transparent, this methodology could find extensions in a broad class of fluids and soft condensed matter systems.

A chiral supramolecular assembly encapsulates the two cationic ruthenium sandwich complexes [CpRu(eta(6)-C(6)H(6))](+) and [CpRu(p-cymene)](+). The host-guest complexes K(11)[CpRu(eta(6)-C(6)H(6)) subset Ga(4)L(6)] (2) and K(11)[CpRu(p-cymene) subset Ga(4)L(6)] (3) were characterized by one- and two-dimensional NMR techniques as well as by electrospray mass spectrometry. Encapsulation of the prochiral complex [CpRu(p-cymene)](+) by the chiral host renders enantiotopic protons diastereotopic as evidenced by (1)H NMR spectroscopy.

Supramolecular assemblies with internal cavities are being developed as nanoscale reaction vessels to protect or modify the reactivity of guest species through encapsulation. Diazonium cations and the tropylium cation were examined for their ability to encapsulate in the tetrahedral [Ga4L6]12− supramolecular assembly. The 4‐(diethylamino)benzenediazonium cation 1 readily formed a 1:1 host−guest complex with this assembly, and this encapsulation prevented 1 from reacting with 2,4‐pentanedione in D2O. The tropylium cation also formed a 1:1 host−guest complex with the [Ga4L6]12− assembly, greatly slowing its decomposition in D2O. Encapsulation in the protected environment of this host cavity alters the reactivity of these guest molecules, giving them greater stability. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

We introduce an alternate route to dynamically polarize the nuclear spin host of nitrogen-vacancy (NV) centers in diamond. Our approach articulates optical, microwave and radio-frequency pulses to recursively transfer spin polarization from the NV electronic spin. Using two complementary variants of the same underlying principle, we demonstrate nitrogen nuclear spin initialization approaching 80% at room temperature both in ensemble and single NV centers. Unlike existing schemes, our approach does not rely on level anti-crossings and is thus applicable at arbitrary magnetic fields. This versatility should prove useful in applications ranging from nanoscale metrology to sensitivity-enhanced NMR.

A broad effort is underway to improve the sensitivity of nuclear magnetic resonance through the use of dynamic nuclear polarization. Nitrogen-vacancy (NV) centers in diamond offer an appealing platform because these paramagnetic defects can be optically polarized efficiently at room temperature. However, work thus far has been mainly limited to single crystals because most polarization transfer protocols are sensitive to misalignment between the NV and magnetic field axes. Here we study the spin dynamics of NV-13 C pairs in the simultaneous presence of optical excitation and microwave frequency sweeps at low magnetic fields. We show that a subtle interplay between illumination intensity, frequency sweep rate, and hyperfine coupling strength leads to efficient, sweep-directiondependent 13 C spin polarization over a broad range of orientations of the magnetic field. In particular, our results strongly suggest that finely-tuned, moderately coupled nuclear spins are key to the hyperpolarization process, which makes this mechanism distinct from other known dynamic polarization channels. These findings pave the route to applications where powders are intrinsically advantageous, including the hyper-polarization of target fluids in contact with the diamond surface or the use of hyperpolarized particles as contrast agents for in-vivo imaging. Nitrogen-vacancy center | hyperpolarization | diamond powder | optical spin pumping | Landau-Zener crossingsNuclear magnetic resonance (NMR) has proven to be a powerful tool in areas ranging from molecular analysis to biomedical imaging. Unfortunately, the attainable nuclear spin polarization is often a small fraction of the possible maximum, thus imposing strict constraints on the minimum sample size and acquisition time. Dynamic nuclear polarization (DNP), i.e, the transfer of magnetization from electron to nuclear spins (1), is a route of growing popularity that substantially mitigates this problem. Enhanced polarization can be attained, e.g., with the aid of dissolved molecular radicals, though the most efficient implementations often rely on freeze-thaw protocols and highfrequency microwave (MW) excitation, which are expensive and technically demanding (2).Adding to the library of DNP platforms, optically active spin-defects in semiconductors are attracting widespread attention as alternative hyperpolarization agents. Among them, the negatively-charged nitrogen vacancy center (NV) in diamond is arguably one of the most promising candidates, since it can be spin-polarized optically to a high degree with only modest illumination intensities and under ambient conditions (3). A variety of protocols have already been implemented to transfer NV spin polarization to surrounding nuclear spins including level-anti-crossing-mediated transfer in the NVground (4) and excited states (5), cross-relaxation with P1-centers (6-8), spin-swap and population trapping (9), amplitude-matched microwave excitation (10,11), and transfer via microwave sweeps (12,13). Despite this progress, however, effic...