Orientation-independent room temperature optical
            <sup>13</sup>
            C hyperpolarization in powdered diamond

Ajoy, Ashok; Liu, Kristina; Nazaryan, Raffi; Lv, Xudong; Zangara, Pablo R.; Safvati, Ben; Wang, Guoqing; Arnold, Don W.; Li, G.; Lin, Anya Maan Yuh; Raghavan, Priyanka; Druga, Emanuel; Dhomkar, Siddharth; Pagliero, Daniela; Reimer, Jeffrey A.; Suter, Dieter; Meriles, Carlos A.; Pines, Alexander

doi:10.1126/sciadv.aar5492

Cited by 128 publications

(216 citation statements)

References 43 publications

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“…Recent work demonstrated efficient 13 C DNP in diamond powders simultaneously exposed to optical illumination and microwave (MW) frequency sweeps (15), but gaining a detailed understanding of the microscopic mechanisms at play has proven subtle due to a complex interplay between the multiple degrees of freedom. Here we examine the dynamics of an NV- 13 C spin pair undergoing simultaneous optical illumination and MW excitation.…”

Section: Nitrogen-vacancy Center | Hyperpolarization | Diamond Powdermentioning

confidence: 99%

Dynamics of frequency-swept nuclear spin optical pumping in powdered diamond at low magnetic fields

Zangara

Dhomkar

Ajoy

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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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...

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Section: Nitrogen-vacancy Center | Hyperpolarization | Diamond Powdermentioning

confidence: 99%

Dynamics of frequency-swept nuclear spin optical pumping in powdered diamond at low magnetic fields

Zangara

Dhomkar

Ajoy

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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“…With the correct balance of paramagnetic defects to fuel DNP without overly accelerating relaxation, hyperpolarized nanodiamond holds the promise of a biocompatible [22,23] MRI imaging agent possessing the advantages over silicon of optical trackability [24][25][26][27] and a readily-functionalized, non-oxidizing surface [28,29]. Although previous works have investigated 29 Si defects and DNP [30], as well as nitrogen-vacancy defects in diamonds, including recent work hyperpolarizing diamond powders via optical methods [31,32], little has been done to investigate the optimum defect concentration for nanodiamond DNP.…”

Section: Introductionmentioning

confidence: 99%

Tailored nanodiamonds for hyperpolarized C13 MRI

et al. 2020

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Nanodiamond is poised to become an attractive material for hyperpolarized 13 C MRI if large nuclear polarizations can be achieved without the accompanying rapid spin-relaxation driven by paramagnetic species. Here we report enhanced and long-lived 13 C polarization in synthetic nanodiamonds tailored by acid-cleaning and air-oxidation protocols. Our results separate the contributions of different paramagnetic species on the polarization behavior, identifying the importance of substitutional nitrogen defect centers in the nanodiamond core. These results are likely of use in the development of nanodiamond-based imaging agents with size distributions of relevance for examining biological processes. arXiv:1909.04842v1 [cond-mat.mes-hall]

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“…Analogously, # = −γ # ⋅ + ⋅ ⋅ corresponds to the Zeeman and quadrupolar terms for the host 14 N nuclear spin of the NV; a similar expression holds for # ) . In addition, ( ) ) is the hyperfine coupling tensor between the NV (P1) electronic spin and the 14 Here, B,B ) stands for the distance between the spins and / , and , define the angular orientation of the inter-spin axis. A similar expression applies to the dipolar interaction between the P1 electron spin and the 1 H spin; we assume the proton is closer to the P1, and correspondingly neglect the dipolar coupling with the NV.…”

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confidence: 99%

Two-Electron-Spin Ratchets as a Platform for Microwave-Free Dynamic Nuclear Polarization of Arbitrary Material Targets

et al. 2019

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Optically-pumped color centers in semiconductor powders can potentially induce high levels of nuclear spin polarization in surrounding solids or fluids at or near ambient conditions, but complications stemming from the random orientation of the particles and the presence of unpolarized paramagnetic defects hinder the flow of polarization beyond the defect's host material. Here, we theoretically study the spin dynamics of interacting nitrogen-vacancy (NV) and substitutional nitrogen (P1) centers in diamond to show that outside protons spin-polarize efficiently upon a magnetic field sweep across the NV-P1 level anti-crossing. The process can be interpreted in terms of an NV-P1 spin ratchet, whose handedness -and hence the sign of the resulting nuclear polarization -depends on the relative timing of the optical excitation pulse. Further, we find that the polarization transfer process is nearly independent of the NV axis orientation, find that the polarization transfer mechanism is robust to NV misalignment relative to the external magnetic field, and efficient over a broad range of electron-electron and electron-nuclear spin couplings, even if proxy spins feature short coherence or spinlattice relaxation times. Therefore, these results pave the route towards the dynamic nuclear polarization of arbitrary spin targets brought in proximity with a diamond powder under ambient conditions.

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Orientation-independent room temperature optical ¹³ C hyperpolarization in powdered diamond

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

Cited by 128 publications

References 43 publications

Dynamics of frequency-swept nuclear spin optical pumping in powdered diamond at low magnetic fields

Dynamics of frequency-swept nuclear spin optical pumping in powdered diamond at low magnetic fields

Tailored nanodiamonds for hyperpolarized C13 MRI

Two-Electron-Spin Ratchets as a Platform for Microwave-Free Dynamic Nuclear Polarization of Arbitrary Material Targets

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Orientation-independent room temperature optical 13 C hyperpolarization in powdered diamond

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

Cited by 128 publications

References 43 publications

Dynamics of frequency-swept nuclear spin optical pumping in powdered diamond at low magnetic fields

Dynamics of frequency-swept nuclear spin optical pumping in powdered diamond at low magnetic fields

Tailored nanodiamonds for hyperpolarized C13 MRI

Two-Electron-Spin Ratchets as a Platform for Microwave-Free Dynamic Nuclear Polarization of Arbitrary Material Targets

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Product

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Orientation-independent room temperature optical ¹³ C hyperpolarization in powdered diamond