First-principles Studies On Energetic, Optical, And Electronic Properties Of Intrinsic Electron-trapping Defects In YAlO₃

YAlO3:Ce3+(YAP:Ce3+) is one of the most popular scintillation materials which have important applications in high energy physics, medical detection and many other fields. The scintillation properties will be affected by the defects in the YAP crystal. For example, luminescence decay time will become longer and luminescence intensity will become weaker. In this thesis, we present theoretical studies on properties of intrinsic electron-trapping defects in YAP by using hybrid density functional theory. The organization is as follows:The first chapter briefly reviews the historical development and applications of scintillators, and the luminescence mechanism of inorganic scintillators. We also describe defect types, defect energy levels, formation energy of defects, and introduce the research background and the main content of this thesis.The second chapter gives an overview of the Hartree-Fock theory and density functional theory, and briefly describes the calculations of physical properties of crystals, such as geometry optimization, calculations of energy band structure and density of states. At the end of this chapter, we introduce the VASP package employed in the present calculations.The third chapter is the main content of this thesis. We firstly used modified PBE0 hybrid density functional theory to calculate the formation energies of isolated defects YAl, AlY, VO and nearest-neighbor defect complexes YAl?Al Y and YAl?VO in various charge states in the YAlO3 crystal. We found that YAl is easier to form than AlY under oxygen-poor condition, which is consistent with the fact that AlY was not observed in the experiment. Secondly, on the basis of the calculated optical transition energies of excitons trapped at YAl, VO, and YAl?VO, we identified the two emission bands observed in the experiment at low temperature. Finally, we studied electronic properties of YAl?VO in the neutral and singly negative charge states. It showed that the extra electron added into the negative charge state of(YAl?VO)? is mainly localized at 4d orbitals of YAl with a two-component feature of its density distribution extending axially along the YAl-VO direction.