The photoconductive excitation spectrum of GaP:N (ZnTe) diodes was measured irradiating the samples from p- and n-side unter forward and reverse bias conditions. The ionization thresholds of S and Te donors as well as transitions from their ground states to excited bound levels with subsequent ionization by the electric field could be seen. The observed minima in the continuum above the ionization threshold are due to phonon assisted fast recombination. The photoconductive signal by irradiation from the p-side is greater and sets on at lower photon energies. In addition, the transmission spectrum was also investigated and interpreted. The green photoluminescence resulting from the recombination of infrared generated carriers in the pn-junction can be applied for infrared imaging if GaP diode wafers of suitable size are employed.