Colour centres in zircon containing both Eu³⁺ and U⁴⁺ ions

Abstract

Single crystals of zircon containing both Eu³⁺ and U⁴⁺ were grown from flux melts cooled at rates varying between 4º/hr and 2º/hr. Irradiation with u.v. develops colour centres only in those regions of a crystal containing Eu³⁺ and U⁴⁺. Fluorescence and absorption spectra measured at temperatures down to 77ºK show that these centres are similar in behaviour to F and F' centres in the alkali halides. They are thought to be related to an exchange coupled pair, U⁴⁺-0²-Eu³⁺, but the experimental data permit only a description in terms of one-electron energy levels. The same basic behaviour is observed for zircon containing U⁴⁺ and any other lanthanide but some interesting differences are described for U⁴⁺, Dy³⁺.