Development of Novel Cesium Chloride-based Ultrafast Inorganic Scintillators for Fast Timing Radiation Detection Applications

Cs₂ZnCl₄ [dicesium zinc tetrachloride] and Cs₃ZnCl₅ [tricesium zinc pentachloride] are relatively new scintillator materials that appear to be promising for use in fast-timing radiation detection applications owing to their 1 to 2 nanosecond decay times. Moreover, they offer several advantages over the state-of-the-art ultrafast inorganic scintillator BaF₂ [barium fluoride]. To fully realize the potential of these novel materials, growth of crystals having improved optical quality must be demonstrated. The mechanism responsible for the ultrafast decay times, core valence luminescence (CVL), in cesium zinc chloride crystals can also be observed in other compounds containing CsCl [cesium chloride]; however, the list of possible materials exhibiting this type of luminescence has not yet been exhausted.

In this dissertation, Cs₂ZnCl₄ and Cs₃ZnCl₅ are first investigated with special attention paid to optimizing synthesis methods and crystal growth parameters to enable growth of large crack-free crystals. We have found that higher light yields than reported in literature can be achieved as a result of superior optical transparency. Additionally, Cs₂ZnCl₄ is successfully grown up to 38 mm in diameter without significant cracking.

Next, we report the discovery of two new scintillators, Cs₂MgCl₄ [dicesium magnesium tetrachloride] and Cs₃MgCl₅ [tricesium magnesium pentachloride], that belong to the same structural families as the Zn-containing compounds. The scintillation mechanism is confirmed to be CVL, and similar benefits regarding light yield, emission wavelengths, and single-component decay times are observed as with Cs₂ZnCl₄ and Cs₃ZnCl₅.

Effects of doping or mixing between Mg²⁺ and Zn²⁺ in these systems are explored as a strategy for improving performance. It is found that light yields of CsMgCl₃ [cesium magnesium trichloride], Cs₂MgCl₄, and Cs₃MgCl₅ can be significantly enhanced when doped with Zn²⁺, directly impacting their timing performance. More importantly, these findings open up possibilities for a new class of bright CVL materials to be discovered moving forward. Possible mechanisms for this impurity-enhanced CVL are discussed.