sentences:  The excitons are loosely bound electron–hole pairs that wander through the crystal lattice until they are captured as a whole by impurity centers.The latter then rapidly de-excite by emitting scintillation light (fast component).In the case of inorganic scintillators, the activator impurities are typically chosen so that the emitted light is in the visible range or near-UV, where photomultipliers are effective.