Physics and Engineering of Radiation Detection

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.