Mössbauer spectroscopy of europium-containing glasses: Optical activator study for x-ray image plates

A fluorozirconate glass (ZBLAN) containing BaCl₂ nanocrystals doped with divalent Eu is a promising material for x-ray image plates for medical diagnosis. Since it is known that Eu²⁺ readily oxidizes to Eu³⁺, which reduces fluorescence efficiency of the image plates, ¹⁵¹Eu Mössbauer spectroscopy was used in this work to monitor the Eu oxidation state of the samples during degradation over time in the presence of ambient humidity. In addition, Mössbauer spectroscopic experiments show that the oxidation state has already changed during the glass melt: The sample made from 5 mol% EuCl₂ contained 78% EuCl₂ + 22% EuCl₃ deduced from the relative areas of the absorption lines. The sample made from 2.5 mol% EuCl₂ + 2.5 mol% EuCl₂ contained 37% EuCl₂ + 63% EuCl₃, i.e. 26% of the original EuCl₂ was oxidized to EuCl₃.