DISCOVERY AND DEVELOPMENT OF RARE EARTH ACTIVATED BINARY METAL HALIDE SCINTILLATORS FOR NEXT GENERATION RADIATION DETECTORS

This work focuses on discovery and development of novel binary halide scintillation materials for radiation detection applications. A complete laboratory for raw materials handling, ampoule preparation, material rapid synthesis screening, single crystal growth, sample cutting, polishing and packaging of hygroscopic halide scintillation materials has been established. Ce³⁺ and Eu²⁺ activated scintillators in three binary systems: Alkali Halide – Rare Earth Halide (AX–REX₃), Alkali Halide – Alkaline Earth Halide (AX–AEX₂) and Alkalin Earth Halide – Rare Earth Halide (AEX₂–REX₃) were systematically studied. Candidates for new scintillation materials in the three systems were selected based on a set of selection rules. A total of 42 Ce³⁺ or Eu²⁺ activated binary halide scintillation material candidates were synthesized and characterized. Among all synthesized candidates, 10 - 15 candidate materials were found to be highly promising in terms of high scintillation light output, fast scintillation decay or desirable emission wavelength.

Three most promising candidates, Cs₃EuI₅, CsGd₂Cl₇:Ce³⁺ and CsSrI₃:Eu²⁺ were selected for single crystal growth and further evaluation. Technologies for single crystal growth of hygroscopic halide scintillation materials were developed. Detailed design of experimental apparatuses was discussed. Single crystals were successfully grown via Bridgman or Vertical Gradient Freeze techniques. Study on optical and scintillation properties was performed. Possibility of using CsGd₂Cl₇:Ce³⁺ as a neutron detector was confirmed.

CsSrI₃:Eu²⁺ shows extraordinary scintillation light output (73,000 ph/MeV), excellent energy resolution (3.9%) and ease for crystal growth. A scaled-up crystal growth was carried out. A bulk crystal of 1” diameter CsSrI₃:Eu²⁺ was successfully grown. Energy level structure and charge carrier traps in CsSrI₃:Eu²⁺ were investigated. Potential of CsSrI₃:Eu²⁺ in various radiation detection applications were evaluated.