We report $β$-detected nuclear magnetic resonance ($β$-NMR) measurements of implanted $^{8}$Li$^{+}$ in a synthetic single crystal of $α$-SiO$_2$ (quartz). At 6.55 Tesla, the spectrum is comprised of a large amplitude broad resonance and a quadrupolar multiplet that is only revealed by an RF comb excitation. The quadrupole splitting is surprisingly small, increases with temperature, and provides information on the implantation site. Supercell density functional theory calculations show that the small EFG is consistent with an in-channel interstitial site (Wyckoff 3$a$). The spin-lattice relaxation is unexpectedly fast and strongly temperature dependent with a diffusive peak above 200 K and a second more prominent relaxation peak at lower temperature. Analysis of the diffusive relaxation yields an activation barrier 178(43) meV for the isolated Li$^{+}$, in the range of other measurements and calculations. To account for many of the other features of the data, it is suggested that some of the implanted ions trap an electron forming the neutral Li$^{0}$, which is stable over a narrow range of temperatures.

Abstract Near‐infrared long‐afterglow nanomaterials hold significant potential in nanomedicine platforms, including targeted drug delivery, precise imaging, and immunotherapy. Improving the particle size distribution and reducing the nanoparticle size to enhance biocompatibility are crucial. Due to the small size effect, reducing the nanoparticle size and improving uniformity typically lead to a decrease in afterglow performance. In this study, near‐infrared long‐afterglow nanoparticles, Zn 2 Ga 2.98 − x Ge 0.75 O 8 :Cr 3+ 0.02 ,Sm 3+ x ( x = 0, 0.02, 0.04, 0.06, 0.08) (ZGGO:Cr 3+ ,Sm 3+ x ), were synthesized using the Sm 3+ ion doping strategy at varying doping concentrations. This work reveals how cation substitution simultaneously affects the nanoparticle size and enhances the near‐infrared long‐afterglow luminescent performance. The Sm 3+ ion doping overcame the increased surface defects caused by the reduced particle size, while simultaneously improving the number of effective luminescent centers by modifying the crystal field environment around the luminescent center. The afterglow intensity and duration of ZGGO:Cr 3+ ,Sm 3+ x nanoparticles were significantly enhanced. The study shows that Sm 3+ ion doping effectively reduces the size of ZGGO:Cr 3+ ,Sm 3+ x nanoparticles while extending the near‐infrared long‐afterglow time by modulating trap depth, the interaction between traps and excited‐state energy levels, and the competition between thermal activation and tunneling processes.