Suppression of afterglow in CsI:Tl by codoping with Eu2+—I: Experimental

Although CsI:Tl is the brightest and most efficient scintillator material ever developed, its use in fast imaging applications has been hindered by its strong and persistent afterglow. Recent experiments, however, have demonstrated that much of this afterglow can be suppressed by the addition of Eu2+ to the CsI host lattice. The magnitude of the effect depends strongly on the duration of the pulse of ionizing radiation that excites the scintillation, but is virtually independent of the intensity of that excitation pulse. The codoping also brings about a measurable red shift in the Tl+ emission, suggesting some degree of spatial correlation between the luminophor and the modifying additive. The observations indicate that the Eu2+ ion exerts its influence not by a quenching process, but rather by introducing a set of electron traps that fundamentally alter the decay kinetics. This is confirmed by the appearance of new glow peaks in the thermoluminescence traces of the codoped material. A consistent mathematical model has been developed to describe the phenomenon, to be discussed in detail in the accompanying paper.