Si was doped with Er by combining Er ion implantation with ion-beam-induced epitaxial crystallization (IBIEC) at 320 degrees C and rapid thermal post-annealing at 980 degrees C. The structural evolution and the Er lattice site occupation during and after this treatment were studied via high-resolution electron microscopy (HREM) and Rutherford backscattering channelling (RBS/C). We obtain approximately 3 x 10(20) Er cm(-3) (about 40% of the implanted dose) in well-defined lattice sites. Photoluminescence (PL) occurs at room temperature. The effect of oxygen co-doping was studied by comparing the PL and lattice locations of Er in Czochralski (CZ), epitaxial, and oxygen-implanted epitaxial hosts.