Rare earth element of erbium implanted into silicon was studied by photoluminescence,and nine spectral lines were observed.The analysis of the symmetry of crystal field shows that the nine spectral lines come from the crystal-field splitting of the transition 4I13/2→4I15/2.We concludethat the symmetry of the two low-energy excited (initial) state levels,in order of increasing energy,are Γ8 and Γ6, from which to the splitting state levels of 4I15/2 nine radiative transitions are allowed.Oxygen codopants can increase greatly the PL intensity of Er3+, but the spectral features are similar,indicating oxygen codopants can enhance the intensity of Td crystal field rather than change the Td symmetry of the crystal field on the Er3+ sites.