[en] Photoluminescence measurements are carried out on a cadmium sulfide (CdS) single crystal grown by using a sublimation method in the temperature range from 20 to 293 K. The peak energies of the free exciton, Ex(A) and Ex(B), are observed at 2.5511 eV and 2.5705 eV, respectively. We find that the temperature dependences of the positions, the intensities, and the linewidths of the exciton peaks fit an empirical equation proposed by Toyozawa, The crystal field of the CdS crystal is observed, and the energy of split gap, Δc_r, is 19.6 meV. The temperature dependence, E_g(T), of the energy band gap of CdS is also discussed