Preparation And Characterization Of Anhydrous EuI₂

Novel halide scintillation crystals such as SrI2:Eu, BaBrI:Eu and CsB2I5:Eu have been attracting increasing interests in recent years because of their high light output (>80000 ph/MeV) and excellent energy resolution (<3%). These crystals have promising application prospects in safety inspection and y cameras. However, the industrialization of these crystals is limited by the high cost and poor purity of anhydrous hailde raw materials. A low-cost route to prepare high purity raw material is critical to future development of these crystals.Anhydrous EuI2 is an essential raw material, which is mostly used as activator. The most common way to produce anhydrous EI2is based on the reaction between europium and HgI2. For HgI2 is highly toxic, this route may cause environmental problem and is difficult to scale up. Therefore, it is necessary to find an economical and environmentally friendly route to prepare anhydrous EuI2.Inspired by previous work of preparing anhydrous LaBr3 by the ammonium-bromide route, this work adopted the ammonium-iodide route to prepare anhydrous EuI2. The thermal decomposition mechanism of EuI3·nH2O was investigated by TGA-DSC and XRD, and the detailed dehydration process was revealed as follows:EuI3·9H2Oâ†'EuI3·8H2Oâ†'EuI3·7H2Oâ†' EuI2·H2Oâ†'EuI2. Valance change of Eu atom was confirmed by fluorescence spectroscopy and the role of NH4I was discussed. It was found that during the preparation,NH4I reacts with EuI2 to form an intermediate product of NH4EuI5with the CsEu2I5 structure, which can protect EuI2 from hydrolysis. NH4I can also react with europium oxide impurities and convert them to EuI2, which helps reduce the oxygen content in the end product. These two aspects guarantee the high purity of the EuI2 product by the ammonium-iodide method, and anhydrous EuI2 with purity of 99.95% was successfully obtained. The product was characterized by Raman spectroscopy, fluorescence spectroscopy, XRD and TGA-DSC. The solid phase transformation of EuI2 was studied by in-situ fluorescence spectroscopy with varying temperatures.