P1 center network in high-pressure high-temperature diamonds is a readily accessible source of nuclear hyperpolarization at 14 T

We investigate nitrogen substitution defects, also known as P1 centers, in type 1b diamonds as a source of electron spin polarization that is readily transferred to 13C nuclear spins within the diamond matrix at 14 Tesla by dynamic nuclear polarization (DNP) at room temperature down to 35 K. The goal was to obtain a quantitative model for clustered P1 centers in diamonds generated under high pressure and high temperature (HPHT). The study relied on frequency-stepped measurements of DNP profiles under magic angle spinning (MAS) using the mm-wave output of a frequency-tunable gyrotron and a regular superconducting NMR magnet set at a single field. The gyrotron output frequency was controlled via the temperature of the gyrotron cavity over 260 MHz centered around 395.3 GHz and had an output power of ~1 W across this range. We observe 13C on/off signal enhancements of up to 700-fold at room temperature under MAS and in static mode, and 130-fold between 35K and 100 K. Modeling of the experimental results revealed the dominant role of P1 clusters harboring inter-P1 dipolar and exchange couplings exceeding 100 MHz in achieving effective 13C DNP at 14.1 T. Clustered P1 centers may be of great utility in generating highly enhanced 13C NMR signal in high-pressure high-temperature diamond as a source of contrast for NMR and MRI applications, or a major decoherence source in quantum sensing applications.