Novel Cs2HfCl6 Crystal Scintillator: Recent Progress and Perspectives

Abstract

Recent progress in Cs2HfCl6 (CHC) crystal production achieved within the last five years is presented. Various aspects have been analyzed, including the chemical purity of raw materials, purification methods, optimization of the growth and thermal conditions, crystal characterization, defect structure, and internal radioactive background. Large volume, crack-free, and high quality CHC crystals with an ultimate scintillating performance were produced as a result of such extensive research and development (R & D) program. For example, the CHC crystal sample with dimensions ∅23 × 30 mm3 demonstrates energy resolution of 3.2% FWHM at 662 keV, the relative light output at the level of 30,000 ph/MeV and excellent linearity down to 20 keV. Additionally, this material exhibits excellent pulse shape discrimination ability and low internal background of less than 1 Bq/kg. Furthermore, attempts to produce a high quality CHC crystal resulted in research on this material optimization by constitution of either alkali ions (Cs to Tl), or main element (Hf to Zr), or halogen ions (Cl to Br, I, or their mixture in different ratio), as well as doping with various active ions (Te4+, Ce3+, Eu3+, etc.). This leads to a range of new established scintillating materials, such as Tl2HfCl6, Tl2ZrCl6, Cs2HfCl4Br2, Cs2HfCl3Br3, Cs2ZrCl6, and Cs2HfI6. To exploit the whole potential of these compounds, detailed studies of the material’s fundamental properties, and understanding of the variety of the luminescence mechanisms are required. This will help to understand the origin of the high light yield and possible paths to further extend it. Perspectives of CHC crystals and related materials as detectors for rare nuclear processes are also discussed.

Advanced Halide Scintillators: From the Bulk to Nano

“…For a review of the Cs 2 HfCl 6 -type scintillators, see the study by Nagorny. [234] First attempts of preparation of ceramic Cs 2 HfCl 6 [235,236] and Tl 2 HfCl 6 [236] showed very promising results.…”

Assessment of Cs2HfCl6 crystal applicability as low-temperature scintillating bolometers by their thermodynamic characteristics

“…The obtained baseline noise resolution (1.84 keV FWHM) of the ZWO phonon channel is similar to values reported for other similar-sized detectors tested in the used setup. 54,55,58,59 At the same time, the LD noise resolution of 0.82 keV FWHM is relatively poor for such type of devices, but it is sufficient to detect scintillation of both ZWO and CHC crystals (according to the CHC light yield estimations at room temperature 10 ). These results are in agreement with what is usually observed for such kinds of detectors, in particular, for similar-sized bolometers.…”

“…The re-invention of the Cs 2 HfCl 6 (CHC) compound as a promising scintillating material in 2015 has initiated extensive R&D activities over the last few years, see ref. 10. As a result of these world-wide studies, high quality CHC crystal samples with dimensions of up to +23 Â 30 mm, an energy resolution of 3.5% FWHM at 662 keV and a LY of 25 000 photons per MeV were obtained.…”

“…Accordingly, each element in the A 2 MX 6 crystalline matrix can be substituted for an alternative element. 10 Therefore, while compounds of the CHC family could be further tuned for the exact needs of high sensitivity gamma-spectroscopy (focused on a high stopping power with large Z eff and fast scintillation kinetics with a decay time of less than 1 μs), it also makes the A 2 MX 6 crystalline matrix flexible to the element of interest that can be embedded for fundamental studies. For instance, controlled element substitution would allow the usage of crystals of the CHC family in high sensitive experiments searching for rare nuclear processes (rare alpha or beta decays and neutrinoless double-beta decay) associated with elements such as Zr, Sn, Pt, Os, Pd and Ru, 13,14 which have never been studied before using the highly sensitive “detector = source” experimental approach.…”

Growth, structure, and temperature dependent emission processes in emerging metal hexachloride scintillators Cs2HfCl6 and Cs2ZrCl6

“…Such a holistic approach enabled targeted optimisation of the manufacturing process that led to the production of large, highquality scintillation crystals with the enhanced performance characteristics. 22,23 Despite a significant number of recent studies on scintillation and luminescence properties of Cs 2 MCl 6 , the information on some physical characteristics of the crystals is incomplete and fragmented. To begin with, there is a lack of accurate crystallographic information for these compounds.…”