Studies of defects in photonic materials

CsI crystals are very effective scintillator materials for particle detectors in high energy physics. Although radiation hard, radiation damage produces colour centres in CsI that reduce light emission and can negatively affect the luminescent centres. Using a combination of Raman and optical absorption spectroscopy applied to CsI crystals bombarded with 1 MeV protons at 300 K, the resulting defects are shown to be F-type centres and interstitial V-centres having the I3− structure and being responsible for absorption bands at 2.7 and 3.4 eV. Isochronal and isothermal annealing experiments show a mutual decay of the F and V-centres. The results are discussed in relation to the formation of interstitial iodine aggregates of various types in alkali iodides.