Time resolved photoluminescence (TRPL) of untreated and heat-treated n-type GaP:S samples has been investigated and compared with data from cathodoluminescence in a scanning electron microscope (CL-SEM). Special attention is given to broad emission bands in the region of 1.8 to 1.6 eV. TRPL shows that dependent on temperature different optical centers are responsible for the luminescence. While the low temperature emission presents a donor-acceptor (D-A) pair behavior above 70 K an excitonic emission dominates with an exponential decay (of the order of seconds at 70 K) in the whole temperature region where it is measured. The temperature behavior of the decay and intensity of these bands leads to the understanding of the processes involved in the luminescence. From the data the distribution of the defects and the levels involved in the emission are discussed. The influence of the annealing in the rearrangement of the defects is analyzed.