Abstract
X irradiation of undoped LiNbO3 causes a photovoltaic current along the crystal c axis, which declines at low temperatures. The ESR of Nb4+ and of trapped hole centers show parallel behavior. Illuminating a ’’saturated’’ crystal with visible light produces another decaying photovoltaic current, accompanied by ESR decrease. It is concluded that valence to conduction band transitions do not contribute essentially to the photovoltaic current.