Bulk Nuclear Hyperpolarization of Inorganic Solids by Relay from the Surface

NMR is a method of choice to determine structural and electronic features in inorganic materials, and has been widely used in the past, but its application is severely limited by its low relative sensitivity. We show how the bulk of proton-free inorganic solids can be hyperpolarized with a general strategy using impregnation dynamic nuclear polarization through homonuclear spin diffusion between low-γ nuclei. This is achieved either through direct hyperpolarization or with a pulse cooling cross-polarization method, transferring hyperpolarization from protons to heteronuclei at particle surfaces. We demonstrate a factor of 50 gain in overall sensitivity for the ¹¹⁹Sn spectrum of powdered SnO₂, corresponding to an acceleration of a factor >2500 in acquisition times. The method is also shown for ³¹P spectra of GaP, ¹¹³Cd spectra of CdTe, and ²⁹Si spectra of α-quartz.