Crystal growth and scintillation performance of Cs2HfCl6 and Cs2HfCl4Br2

The crystal growth and behavior of a high-performance, non-hygroscopic scintillator, Cs2HfCl6 (CHC) and its variant, Cs2HfCl4Br2 (CHCB) are presented in this work. CHC and CHCB were prepared by melt compounding of sublimed HfCl4 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 HfCl4 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.