Irradiation of 2,3 DN single crystals by 5 nsec light pulses from a nitrogen laser (337 nm) and by 20 nsec light pulses from a Q-switched ruby laser (347 nm, second harmonic) respectively, causes generation of free holes. Centers which are most probably associated with crystal defects are electronically excited by the incident light directly or by energy transfer from the primary excited 2,3 DN. The excited centers are quenched by charge transfer interaction with 2,3 DN. Mobile holes are separated from the localized negatively charged centers subject to the applied electric field. The centers are distributed uniformly over most of the volume, but in a region closer than 1 μm to the surface the concentration increases rapidly. In this surface layer also a high density of hole traps are found to exist, which are responsible for the temperature dependent rise of the photocurrent pulses below room temperature. At high current densities recombination between ionized centers and drifting holes becomes important. The recombination coefficient is found to be 10 -5 cm 3 /sec. Analysation of the fast (60 nsec) rise of the photocurrent pulses above room temperature gives information about the lifetime of the excited centers and about the lifetime of the singlet excitons in the surface layer. Values of ≈ 30 nsec for the centers and ≲ 10 nsec for the excitons are found. The volume lifetime of the singlet excitons is measured to be 80 nsec.