The complicated structure of photodetectors, which enable to convert IR radiation to the VIS one has not been clarified with all aspects; in fact, the use of different semiconductors and the effects of different plasma parameters to the IR enhancement and hysteresis phenomena has not been understood, yet. Within this context, the optoelectronic properties of a gallium phosphate (GaP) photodetector were experimentally explored in the IR image converter cell. It was observed that GaP material exhibits various interesting behaviors, when the applied voltage is increased gradually. The discharge current I changes at different illumination intensities, when an external IR light source was used. Moreover, the tail region of the absorption spectrum of GaP played an important role to characterize current under various illuminations L-n. It was proven in the sweep up/down voltage tests that a clear hysteresis behavior persists for a wide voltage range. This feature makes this photodetector been a good candidate for the semiconductor memory studies and strictly related to negative differential resistance (NDR). In addition, the effects of plasma parameters such as the gas pressure p and the interelectrode distance d were also explored in detail for the first time and it was found that p affects the hysteresis behavior dominantly in the converter.