Photoluminescence (PL) spectra ofEr3+in an Er-doped silicon film were recorded at 2 and 77 K over the wavelength range from 1.52 to 1.68 &mgr;m, which includes optical transitions between theEr3+4I13/2and4I15/2manifolds. These spectra were then analyzed to determine the nature of the electrostatic field at the site of the Er ion that governs the ion’s optical behavior. The PL spectra were analyzed three different ways: by considering theEr3+ions to be occupying sites ofTd,C3,orD2dpoint group symmetry. Transition energies and magnetic dipole transition probabilities were calculated for each case by diagonalizing a Hamiltonian representing the free-ion and crystal-field interactions in a Russell–Saunders basis of states spanning the lowest 15Jmultiplets of the4f11electronic configuration ofEr3+.Crystal-field parameters were varied in each case to find the best agreement with the experiment. Our results showed that the site symmetry of theEr3+ions most consistent with the data isD2d.For this case, the rms deviation between the experimental and calculated energy levels is3.3 cm−1with the calculated magnetic dipole transition probabilities in qualitative agreement with the experiment. ©1997 American Institute of Physics.