Two photoluminescent defects associated with Er+3-doped Si are (i) a high-temperature defect (which appears after annealing at ∼900 °C and produces five photoluminescence lines), and (ii) a low-temperature defect (which is created at lower annealing temperatures in addition to the high-temperature defect and yields four photoluminescence lines). We conclude that both defects are at Er sites of tetrahedral symmetry, one substitutional and the other interstitial, and that the crystal-field split ground-state levels of Er+3at either site are of the symmetries (in order of increasing energy) &Ggr;6, &Ggr;8, &Ggr;8, &Ggr;7, and &Ggr;8. We predict that the highest &Ggr;8level of the low-temperature defect has not yet been resolved, which is why that defect exhibits only four levels. The symmetries of the excited (initial) state levels, in order of increasing energy, are predicted to be &Ggr;8, &Ggr;6, &Ggr;6, &Ggr;8, and &Ggr;7. We speculate that the high-temperature defect’s Er is at an interstitial site, while the low-temperature defect’s Er is substitutional. ©1997 American Institute of Physics.