Study Of The Point Defect In The Gd₂SiO₅ Crystal

Gadolinium silicate Gd2 Si O5 crystal(GSO) is a good optical host material. It shows different functions doped with different impurity ionic. For instance, GSO crystals doped with impurity ions such as Pr3+, Eu3+, Tb3+, especially Ce3+, are applied as scintillation crystals. It is widely applied to oil detection image, nuclear medicine(PET) and high-energy nuclear physics. In addition, GSO crystal doped with Yb3+ ions may serve as a femtosecond solid laser gain medium. For the moment, the experimental and theoretical studies of GSO crystals are rare, but the theoretical study of GSO crystal is the foundation of further studying the doping mechanism. Therefore, the first principle calculation of the GSO crystal is particularly important. In the crystal shell Gd-4f orbital is half filled, so the GSO is a strong correlation system, which brings some troubles in computation. Density functional theory(DFT) is recognized as one of the most commonly used method in physical and chemical fields. In the crystal shell Gd-4f orbital is half filled, so the GSO is a strong correlation system, which brings some troubles in computation. In this work, the DFT+U approach for the strong correlation system will be employed in the calculations of GSO crystal. Two kinds of predominant point defects in GSO crystal are simulated, and their structural properties and electronic structures have been analyzed detailedly.The thesis is composed of six sections:1) Introduction, introduces the study background and situation of GSO crystal, the purpose and the works of this thesis.2) Theoretical basis, introduces the density functional theory and the plane wave pseudo-potential method as well as the calculation software: VASP.3) Calculation of the electronic structures and the elastic properties of the perfect GSO crystal with GGA+U approach.4) Calculation of the electronic structures of the GSO containing oxygen vacancy by VASP.5) Calculation of the electronic structures of the GSO containing oxygen vacancy by VASP.6) Conclusion of the thesis.