Room-temperature hyperpolarization of polycrystalline samples with optically polarized triplet electrons: pentacene or nitrogen-vacancy center in diamond?

Abstract

We demonstrate room-temperature <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi></mml:mi><mml:mn>13</mml:mn></mml:msup></mml:math>C hyperpolarization by dynamic nuclear polarization (DNP) using optically polarized triplet electron spins in two polycrystalline systems: pentacene-doped [carboxyl-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi></mml:mi><mml:mn>13</mml:mn></mml:msup></mml:math>C] benzoic acid and microdiamonds containing nitrogen-vacancy (NV<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi></mml:mi><mml:mo>-</mml:mo></mml:msup></mml:math>) centers. For both samples, the integrated solid effect (ISE) is used to polarize the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi></mml:mi><mml:mn>13</mml:mn></mml:msup></mml:math>C spin system in magnetic fields of 350-400 mT. In the benzoic acid sample, the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi></mml:mi><mml:mn>13</mml:mn></mml:msup></mml:math>C spin polarization is enhanced by up to 0.12 % through direct electron-to-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi></mml:mi><mml:mn>13</mml:mn></mml:msup></mml:math>C polarization transfer without performing dynamic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi></mml:mi><mml:mn>1</mml:mn></mml:msup></mml:math>H polarization followed by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mi></mml:mi><mml:mn>1</mml:mn></mml:msup><mml:mi>H</mml:mi><mml:msup><mml:mo>-</mml:mo><mml:mn>13</mml:mn></mml:msup><mml:mi>C</mml:mi></mml:mrow></mml:math> cross-polarization. In addition, the ISE has been successfully applied to polarize naturally abundant <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi></mml:mi><mml:mn>13</mml:mn></mml:msup></mml:math>C spins in a microdiamond sample to 0.01 %. To characterize the buildup of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi></mml:mi><mml:mn>13</mml:mn></mml:msup></mml:math>C polarization, we discuss the efficiencies of direct polarization transfer between the electron and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi></mml:mi><mml:mn>13</mml:mn></mml:msup></mml:math>C spins as well as that of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mi></mml:mi><mml:mn>13</mml:mn></mml:msup><mml:mi>C</mml:mi><mml:msup><mml:mo>-</mml:mo><mml:mn>13</mml:mn></mml:msup><mml:mi>C</mml:mi></mml:mrow></mml:math> spin diffusion, examining various parameters which are beneficial or detrimental for successful bulk dynamic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi></mml:mi><mml:mn>13</mml:mn></mml:msup></mml:math>C polarization.