The information on solid-state (internal defect) can be contactlessly obtained from the phenomenon that light emission occurs from X-ray-irradiated KCl:Eu2+ single crystals. A new peak appears around 330 K on the thermoluminescence (TL) glow curve of the X-ray-irradiated crystals after the quenching from 473 to 773 K to room temperature. The peak is termed 330 K peak here. It is considered that the electrons released from F-centres (trapped electrons) lying in the dislocation segments are captured in the dislocation (linear crystal defect) zone and move along the dislocation line in the crystal. And further, the electrons combine with Eu3+ ions near the dislocation segments at 330 K. The variations of the TL glow curve and initial dislocation density under the influence of heat treatment confirm that the 330 K peak depends on the dislocations in the crystal.