15th International Conference on Muon Spin Rotation, Relaxation and Resonance

We present high magnetic field $\beta$NMR measurements of $^8$Li$^+$ implanted in single crystals of sapphire, a commonly used backing material for other samples. From the well-resolved quadrupolar splitting, we extract the electric field gradient (EFG) at the implanted $^8$Li$^+$ site. Comparison with supercell density functional theory calculations of the EFG allows us to identify the octahedral interstitial site as the most likely candidate. In contrast to the zero field $\beta$NQR spectra, only a single site is evident at high field. We discuss possible explanations for this discrepancy. The high field spin lattice relaxation is extremely slow ($1/T_1 < 0.02$ s$^{-1}$) from 4 to 300 K. This regime, where cross relaxation to the $^{27}$Al nuclear spins is quenched, extends down to at least 2.2 Tesla.