Date of Award

5-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Charles L. Melcher

Committee Members

James R. Morris, Jason P. Hayward, Peter Cohen, Mariya Zhuravleva

Abstract

Scintillation materials are in great demand for radiation detection applications. In this dissertation work, a series of new metal halide scintillation materials are presented. A comprehensive procedure of candidate scintillator screening, single crystal growth, scintillation properties characterizations, and scintillation mechanism investigations are established. The potential candidate materials are firstly synthesized by melt-freeze method to form polycrystalline. The scintillation properties of the polycrystalline specimen are characterized to select the most promising scintillators. The selected scintillators are grown into single crystals. Protocols including raw materials purification, materials pre-mixing, ampoule design, and furnace manipulation are developed to improve the scintillators’ performance.

Cerium-doped ternary and quaternary metal halide scintillators are proposed and studied systematically. Among them, the single crystal growth, scintillation properties, dopant concentration optimization, luminescence spectroscopic analyses, and scintillation mechanisms of Ce-doped Cs3LaCl6 [cesium lanthanum chloride], Cs3LaBr6 [cesium lanthanum bromide], Cs2NaLaBr3I3 [cesium sodium lanthanum bromide iodide], and Cs2NaYBr3I3 [cesium sodium yttrium bromide iodide] are investigated. Both Ce-doped Cs3LaCl6 and Cs3LaBr6have moderate light yield between 20,000 to 35,000 photons per MeV with optimized Ce concentration. They have stable photoluminescence and radioluminescence excitation/emission in a wide range of temperature from 40 K [kelvin] to 500 K, and this allows them to be good candidates for high temperature radiation detection applications, such as oil well logging. Mixed-anion can be a useful approach to engineer the halide scintillators for higher light yield and better energy resolution, which is proven by new elpasolite scintillators Ce-doped Cs2NaLaBr3I3 and Cs2NaYBr3I3. They have superior energy resolution and higher light yield compared with the un-mixed elpasolite scintillators. More interestingly, the undoped mixed-anion crystals also have scintillation response. This indicates alternative scintillation process in these crystals other than the direct luminescence from the dopant.

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