DEFECT CENTERS IN HEAVY-METAL FLUORIDE GLASSES - A REVIEW

A variety of paramagnetic defect centers are induced in heavy-metal fluoride glasses by ionizing radiations. The most fundamental of these are the F centers (neutral fluorine vacancies, which tend to associate with Zr4+ or Hf4+ ions) and the H centers (interstitial atomic fluorines, which in pure glasses inevitably combine with normal network F- ions to form F-3(2-) and/or F2- species). The most stable defects are those associated with impurities. The latter include F-type centers associated with Fe3+ and the following H-type centers: (FCl)-, Cl2-, (FBr)-, Br2-, O-(?), and O2-. All of these defects have been well characterized by electron spin resonance.