The common charge states of Sn are 2+  and 4+. While charge neutrality considerations favour 2+  to be the natural charge state of Sn in ZnO, there are several reports suggesting the 4+  state instead. In order to investigate the charge states, lattice sites, and the effect of the ion implantation process of dilute Sn atoms in ZnO, we have performed Sn emission Mössbauer spectroscopy on ZnO single crystal samples following ion implantation of radioactiveIn (T =  2.4 min) at temperatures between 96 K and 762 K. Complementary perturbed angular correlation measurements onCd implanted ZnO were also conducted. Our results show that the 2+  state is the natural charge state for Sn in defect free ZnO and that the 4+  charge state is stabilized by acceptor defects created in the implantation process.

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57 Fe emission Mössbauer spectroscopy has been applied to study the lattice location and properties of Fe in gadolinium gallium garnet Gd 3 Ga 5 O 12 (GGG) single crystals in the temperature interval 300 -563 K within the extremely dilute (<10 −4 at.%) regime following the implantation of 57 Mn (T1 / 2 = 1.5 min.) at ISOLDE/CERN. These results are compared with earlier Mössbauer spectroscopy study of Fe-doped gadolinium gallium (GGG), with implantation fluences between 8×10 15 and 6×10 16 atoms cm −2 . Three Fe components are observed in the emission Mössbauer spectra: (i) high spin Fe 2+ located at damage sites due to the implantation process, (ii) high spin Fe 3+ at substitutional tetrahedral Ga sites, and (iii) interstitial Fe, probably due to the recoil imparted on the daughter 57 * Fe nucleus in the β − decay of 57 Mn. In contrast to high fluence 57 Fe implantation studies the Fe 3+ ions are found to prefer the tetrahedral Ga site over the octahedral Ga site. No annealing stages are evident in the temperature range investigated. Despite the very low concentration, high-spin Fe 3+ shows fast spin relaxation, presumably due to an indirect interaction between nearby gadolinium atoms.