The other type of gamma-ray detector is a scintillation detector. In a semiconductor detector electron-hole pairs are collected by applying a voltage. In a scintillation detector the collection process is different.

When a gamma-ray photon deposits its energy in a luminescent material (scintillator), it causes electrons to be excited to higher energy levels in the material. 

In some cases the energy given to the electron is not sufficient to raise it to the conduction band and the electron and hole can remain electrostatically attracted to each other in an entity called an exciton.

These excited electrons may decay by emitting electromagnetic radiation. If this radiation is in the optical wavelength range it can be detected by a photomultiplier tube where it generates an electrical signal.

Use the simulation opposite to demonstrate this.

See here for scintillator materials used for gamma-ray detection...