Detection of the Surface of Crystalline Y2O3 Using Direct 89Y Dynamic Nuclear Polarization

Nuclei with low gyromagnetic ratio (gamma) present a serious sensitivity challenge for nulear magnetic resonance (NMR) spectroscopy. Recently, dynamic nuclear polarization (DNP) has shown great promise in overcoming this hurdle by indirect hyperpolarization (via H-1) of these low-gamma nuclei. Here we show that at a magnetic field of 9.4 T and cryogenic temperature of about 110 K direct DNP of Y-89 in a frozen solution of Y(NO3)(3) can offer signal enhancements greater than 80 times using exogeneous trityl OX063 monoradical by satisfying the cross effect magic angle spinning (MAS) DNP mechanism. The large signal enhancement achieved permits Y-89 NMR spectra of Y2O3 and Gd2O3-added Y2O3 materials to be obtained quickly (similar to 30 min), revealing a range of surface yttrium hydroxyl groups in addition to the two octahedral yttrium signals of the core. The results open up promises for the observation of low gyromagnetic ratio nuclei and the detection of corresponding surface and (sub-)surface sites.