The invention relates to a radiation detector (1), an imaging system and a related method for radiation detection. The detector comprises a direct conversion material (2) for converting x-ray and/or gamma radiation into electron-hole pairs by direct photon-matter interaction. The detector comprises an anode (3) and a cathode (4) arranged on opposite sides of the direct conversion material (2) such that the electrons and holes can respectively be collected by the anode and cathode. The cathode is substantially transparent to infrared radiation. The detector comprises a light guide layer (5) on the cathode at a side of the cathode that is opposite of the direct conversion material, in which the light guide layer is adapted for distributing infrared radiation over the direct conversion material. The detector comprises a reflector layer (6) arranged on the light guide layer (5) at a side opposite of the cathode, in which the reflector layer is adapted for substantially reflecting infrared radiation. The detector comprises at least one light emitter (7), abutting on and/or integrated in the light guide layer (5), for emitting infrared radiation into the light guide layer.