Dehydration and oxidation in the preparation of Ce-doped LaCl3 scintillation crystals

Ce3+ activated LaCl3 is a promising scintillation crystal for radiation detection. The starting raw materials used to grow LaCl3 crystals are rather hygroscopic and XRD proves that LaCl3·7H2O and LaCl3·3H2O are two main compounds in the raw materials. Five endothermal peaks, 100.4 °C, 156.0 °C, 181.0 °C, 210.6 °C and 840 °C, are observed in the DTA curves, they are corresponding to the thermal dehydration effect of crystallized water and melting. The process of dehydration is described to be 7 → 6 → 3 → 1 → 0. In the dehydration process, little amount of LaOCl phase can be identified, its formation is related to the oxidation of LaCl3 at high temperature: LaCl3·nH2O → LaOCl + HCl↑. In addition, LaOCl phases also appear in the grown crystals, they are suggested to be responsible for the transmission loss of the crystals. The oxidation temperature of LaCl3 with oxygen is much lower than that with water.