Ammonium-iodide route to anhydrous EuI2: mechanism and preparation

Anhydrous EuI2 is an essential raw material for novel Eu2+-doped halide scintillators such as SrI2:Eu, CsBa2I5:Eu and BaBrI:Eu. An efficient and economic method to produce high purity anhydrous EuI2 is critical for future development and applications of these scintillators. In this paper, the ammonium-iodide route to anhydrous EuI2 was investigated, and anhydrous EuI2 with purity of 99.95 wt.% was successfully prepared. The dehydration mechanisms of europium iodide hydrate and its mixture with NH4I were comparatively investigated by X-ray diffraction (XRD), thermal analysis and fluorescence spectroscopy. The thermal decomposition process of individual europium iodide hydrate was revealed as follows: EuI3·9H2O→EuI3·8H2O→EuI3·7H2O→EuI2·H2O→EuI2, and the hydrolysis mechanism of europium hydrate was comprehensively studied. When europium iodide hydrate was dehydrated with NH4I, NH4Eu2I5 formed as an intermediate product, and the hydrolysis of EuI2 was effectively restrained. The role of NH4I as an iodination agent was also discussed.

Graphical AbstractAs-prepared EuI2Figure optionsDownload as PowerPoint slide