Date of Award

12-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Materials Science and Engineering

Committee Chair/Advisor

Luiz G. Jacobsohn

Committee Member

Kyle S. Brinkman

Committee Member

Jianhua Tong

Committee Member

Colin McMillen

Abstract

Optically stimulated luminescence (OSL) dosimeters have attracted increasing attention due to advantages over TL dosimeters, including no thermal quenching and higher sensitivity. Nevertheless, currently, there are only two commercially available OSL dosimeters, BeO and Al2O3:C. An OSL dosimeter requires low effective atomic number (Zeff < 16), at least one type of recombination center and one type of trap, and UV~blue emission. In this dissertation, motivated by the search of new OSL dosimetric materials, a systematic investigation of alumina (Zeff = 11.3) and magnesium aluminate spinel (Zeff = 11.2) based materials was performed in terms of the engineering of the recombination centers and electronic traps. Microstructural characterization was executed by means of X-ray diffraction (XRD) and Raman spectroscopy. Luminescence was characterized under X-ray excitation (radioluminescence; RL) at ambient and high temperatures, and by thermoluminescence (TL) and OSL measurements.

In Chapter 3, dopants Tm, Bi, Sb, Ga and Ti were incorporated in Al2O3 as new recombination centers, revealing Sb to be the most promising one because of its intense band centered at 410 nm. Another strategy to engineer the intrinsic luminescence of Al2O3 was to manipulate the relative concentrations of F-type centers in the host through sucrose adding into precursors together with calcination under reducing atmosphere.

In Chapter 4, manipulation of recombination centers and electronic traps was studied by using magnesium aluminate spinel as a host. Varying the MgO:Al2O3 ratio, thermal processing at different temperatures and Li substituting for Mg could all manipulate intrinsic defects within the magnesium aluminate spinel material, thus affecting the OSL behavior. The stoichiometric spinel presented superior OSL dose response, calcination temperature led to progressive crystallization and impurity activation concomitant to an increase of intensity of all RL bands. The so far unknown 400 nm band was identified to be resulting from anti-site defects. Li substitution for Mg could manipulate anti-site defects and Mg vacancies. Ce incorporation was used to engineer recombination centers in the MgAl2O4 spinel, leading to a new luminescence band resulting from two distinct luminescence centers related to Ce3+.

In summary, engineering of recombination and/or trapping centers plays an important role on luminescence response, including OSL signal. A better manipulation of recombination and/or trapping centers could significantly facilitate the development of new OSL dosimetric materials with improved performance.

Available for download on Wednesday, November 30, 2022

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