Charge transfer processes in transition metal ions, which are doped in wide band-gap II-VI semiconductors, are of great interest because of possible application for novel optical and spintronic devices. In this work we study 2+ -> 3+ photoionization transition (PT) of iron ions in ZnSSe:Fe bulk crystals in temperature range of 2 - 100 K. By monitoring changes of the Fe³⁺ ESR (electron spin resonance) signal under external illumination we are able to determine energies of Fe²⁺ -> Fe³⁺ + e_CB transition in different ZnSSe host crystals. At low temperature we observe metastable (in part) population of photo-excited Fe³⁺ centers. Free electrons created in the conduction band under the 2+ to 3+ ionization of iron, are efficiently trapped by donor centers. We observe also appropriate photoionization bands in low temperature absorption spectra. Previous studies have shown that the iron PT is an efficient channel for excitation of the Fe²⁺ intra-ion emission in ZnS:Fe at low temperature.