Crystal growth and scintillation performance of Cs2HfCl6 and Cs2HfCl4Br2

The crystal growth and behavior of a high-performance, non-hygroscopic scintillator, Cs 2 HfCl 6 (CHC) and its variant, Cs 2 HfCl 4 Br 2 (CHCB) are presented in this work. CHC and CHCB were prepared by melt compounding of sublimed HfCl 4 with CsCl and CsBr to produce material for Bridgman growth. The resulting 1 cm dia. and 1 in. dia. CHC crystals showed in certain parts evidence of CsCl as a secondary phase—a result of a non-stoichiometric (CsCl-rich) melt composition caused by the high vapor pressure of HfCl 4 during compounding. This was verified using micro X-ray fluorescence spectrometry. There is also evidence of a secondary phase in CHCB, which has been presented for the first time. A clear CHC sample had a light yield and energy resolution of 30,000 ph/MeV and 3.3%, respectively, and decay components of 0.39 and 3.9 µs. A sample of CHCB with a secondary phase present in the core had a light yield and energy resolution of 18,600 ph/MeV and 4.4%, and with decay components of 0.38 and 2.0 µs for CHCB. Both crystals showed minimal moisture sensitivity.