Photoluminescence measurements in sulfur-doped silicon samples reveal new luminescence lines at 1.1439 eV (S1), 1.1150 eV (S2), and 1.0858 eV (S1TO). [S1TO is the transverse optical (TO) phonon replica of the S1 line.] The sharp luminescence lines result from the recombination of excitons bound to two different centers. The S1 line was found to have a thermal ionization energy of 12.0 meV, which corresponds directly to the spectroscopically determined binding energy of the bound exciton. A correlation of the binding centers with the sulfur donor levels is suggested.