Iowa State University Capstones, Theses and Graduate Theses and Dissertations Dissertations 2015 Computational design of new scintillator chemistries and defect structures Hyung jin Kim Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/etd Part of the Materials Science and Engineering Commons, and the Mechanics of Materials Commons Recommended Citation Kim, Hyung jin, "Computational design of new scintillator chemistries and defect structures" (2015). Graduate Theses and Dissertations. 14395. https://lib.dr.iastate.edu/etd/14395 This Thesis is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Computational design of new scintillator chemistries and defect structures by Hyung jin Kim A thesis submitted to the graduate faculty in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Major: Materials Science and Engineering Program of Study Committee: Krishna Rajan, Major Professor Kristen Constant Ganesh Balasubramanian Iowa State University Ames, Iowa 2015 Copyright © Hyung jin Kim, 2015. All rights reserved. ii DEDICATION To my parents, my sister and uncle Uk-keun. iii TABLE OF CONTENTS Page LIST OF FIGURES ................................................................................................... v LIST OF TABLES ..................................................................................................... vii ACKNOWLEDGEMENTS ....................................................................................... viii ABSTRACT………………………………. .............................................................. ix CHAPTER 1 INTRODUCTION .......................................................................... 1 1.1. Objective ....................................................................................................... 1 1.2. Background of Scintillator ............................................................................ 1 1.2.1. What is a Scintillator? ........................................................................ 1 1.2.2. History of Scintillator ........................................................................ 2 1.2.3. Mechanism of Inorganic Scintillator ................................................. 5 1.2.3.1. Absorption of γ-rays ............................................................. 6 1.2.3.2. Electron-hole Pair Multiplication ......................................... 7 1.2.3.3. Energy Transportation .......................................................... 8 1.2.3.4. Luminescence ....................................................................... 9 1.2.3.5. Efficiency .............................................................................. 9 1.2.3.6. Decay Time ........................................................................... 10 1.2.4. Considerations for the Search for New Scintillators.......................... 11 1.3. Material Systems ........................................................................................... 11 1.4. Material Screening Logic .............................................................................. 12 1.5. Outline of the Thesis ..................................................................................... 14 References ...................................................................................................... 14 CHAPTER 2 THEORY: THE BACKGROUND OF DENSITY FUNCTIONAL THEORY ....................................................................... 22 2.1. What is Density Functional Theory? ............................................................ 22 2.2. The Hohenberg-Kohn Thoerem .................................................................... 25 2.3. Kohn-Sham Equation .................................................................................... 26 2.4. Exchange-correlation Functional .................................................................. 28 2.5. Approximation Method ................................................................................. 29 2.6. Plane-wave Pseudopotential ......................................................................... 30 2.7. Pseudopotentials ........................................................................................... 33 iv 2.8. Ultrasoft Pseudopotential .............................................................................. 35 References ........................................................................................................ 35 CHAPTER 3 METHOD: CASTEP SOFTWARE ................................................ 37 3.1. CASTEP Background ................................................................................... 37 3.1.1. Introduction ........................................................................................ 37 3.1.2. Background ........................................................................................ 37 3.1.3. Capabilities ........................................................................................ 38 3.1.4. Example ............................................................................................. 39 3.2. Example of Yttrium Aluminum Garnet (YAG) Calculation ........................ 45 References ........................................................................................................ 48 CHAPTER 4 DFT CALCULATION RESULTS ON GARNET HOST LATTICES ... ................................................................................ 49 4.1. Prior Informatics Screening on Garnets ........................................................ 49 4.2. Yttrium Aluminum Garnet (YAG) ............................................................... 51 4.3. Terbium Aluminum Gallium Garnet ............................................................ 54 4.4. Summary of Garnet Host Lattice Design ...................................................... 57 References ........................................................................................................ 58 CHAPTER 5 DFT CALCULATION RESULTS ON CO-DOPED PEROVSKITES .................................................................................... 59 5.1. Advantage of Doping .................................................................................... 59 5.2. Prior Informatics Screening on Perovskites .................................................. 59 5.3. Yttrium Aluminum Perovskite (YAP) .......................................................... 62 5.4. Co-doped Yttrium Aluminum Perovskites ................................................... 64 References ........................................................................................................ 69 CHAPTER 6 SUMMARY AND CONCLUSIONS ............................................. 70 v LIST OF FIGURES Page Figure 1.1. History of discovery of inorganic scintillator materials .......................... 3 Figure 1.2. Decay time versus light yield of contemporary inorganic scintillators ... 5 Figure 1.3. Decay time versus bandgap of contemporary inorganic scintillators ...... 10 Figure 1.4. An example of garnet structure ............................................................... 11 Figure 1.5. An example of perovskite structure ......................................................... 12 Figure 1.6. A schematic illustration of material search logic .................................... 13 Figure 3.1. Build crystal dialog.................................................................................. 39 Figure 3.2. Add atoms dialog ..................................................................................... 40 Figure 3.3. Primitive cell of an example AlAs crystal ............................................... 41 Figure 3.4. CASTEP calculation dialog ..................................................................... 41 Figure 3.5. Partial density of states of an example CO molecule .............................. 43 Figure 3.6. Flow chart of a CASTEP calculation ...................................................... 44 Figure 3.7. Optimization convergence graph of YAG ............................................... 47 Figure 3.8. Energy of the system during geometry optimization iterations............... 47 Figure 4.1. Informatics screening step on garnets ..................................................... 50 Figure 4.2. Unit cell structure of Y3Al5O12 ................................................................ 51 Figure 4.3. The band structure of YAG ..................................................................... 53 Figure 4.4. The converged YAG structure................................................................. 54 Figure 4.5. Unit cell structure of Tb3Al2Ga3O12 ........................................................ 55 Figure 4.6. Band structure of Tb3Al2Ga3O12 .............................................................. 56 vi Figure 4.7. Decay time and light yield of new Tb3Al2Ga3O12 garnets and other garnets ...................................................................................... 57 Figure 5.1. Informatics screening steps on perovskite co-dopant chemistries .......... 61 Figure 5.2. Unit cell structure of YAP ....................................................................... 62 Figure 5.3. Band