352 Chapter 6. Scintillation Detectors and Photodetectors
Scintillation
Light
Luminescence
Radiation Center
Incident
Electron Hole
Eg
E
Valence Band
Conduction Band
Exciton
Exciton Band
Figure 6.3.1: Principle of exciton luminescence from a partially
bound exciton in an inorganic scintillator. If the electron moves
up to the conduction band, the exciton thus created will be free to
move around. In either case the electron can eventually get trapped
by a luminescence center through self trapping or charge transfer
process.
A.2 DopantLuminescence
Some scintillators are loaded with an impurity ordopantto enhance its scintillation
properties. If an electron gets trapped in a dopant level and from there falls into
the lower luminescence level, scintillation light is emitted. The process is shown in
Fig.6.3.2.
A.3 CoreValenceBandLuminescence...............
If the incident radiation deposits enough energy along its track into the lattice, it
can elevate electrons from the deep core valence band to the conduction band (see
Fig.6.3.3). An electron leaving the core valence band leaves behind a vacancy or
hole. To stabilize the system a valence band electron quickly fills this vacancy. This
results in the emission of scintillation light. The process is generally known as core
valence band luminescence.
6.3.B RadiationDamage
Let us now discuss the effects of radiation on inorganic scintillators. Although
in general the properties of inorganic scintillators deteriorate with absorbed dose
but special materials have been developed that show significant radiation hardness.