ABSTRACT
This chapter focuses on transient luminescent phenomena, that is, time-dependent emission processes such as luminescence after-glow (phosphorescence), thermally stimulated emission (thermal glow), photo (infrared)-stimulated emission, and photoquenching. All of these phenomena are related to a quasistable state in a luminescent center or an electron or hole trap. Luminescence is divided into fluorescence and phosphorescence according to the duration time of the after-glow. If one of the excited states of a luminescent center is a quasistable state (an excited state with very long lifetime), a percentage of the centers will be stabilized in that state during excitation. After excitation has ceased, after-glow is caused by the thermal activation of the state. The electrons captured by traps may cause phosphorescence (long afterglow) when they are thermally reactivated into the conduction band and then radiatively recombined at an emitting center. The decay time of phosphorescence due to traps can be as long as several hours and is often accompanied by photoconductive phenomena.
