A radiation detector and a method of operating the radiation detector. The radiation detector includes: a photoconductive layer between the array substrate and the counter electrode and having a particle-in-binder (PIB) structure in which a photoconductive particle and a binder are mixed; and an optical unit for providing light energy to the photoconductive layer to detrap a charge trapped in an interface between the photoconductive particle and the binder. The light energy includes ultraviolet rays and/or visible rays.