Role Of Intrinsic Defects On The Luminescence Of Mn Doped ZnGa₂O₄

Long afterglow material is a special photoluminescent material that can continue to illuminate after the excitation stops,mainly used in the field of safety illumination and biomedical test.In this paper,we have studied the role of intrinsic defects in ZnGa₂O₄:Mn system about the self-activated luminescence,Mn doping mechanism and long persistent luminescence in depth.In the first chapter,we briefly introduce the application,type and luminescence mechanism of long afterglow materials.Then we expound the structure and research background at home and abroad of ZnGa₂O₄ system.Finally,the main research contents and methods are introduced.In the second chapter,we mainly introduce the first-principles methods and concepts based on density functional theory,and the calculation software used in this work.In the third chapter,we describe the electronic structure and stable thermodynamic phase diagram of pure ZnGa₂O₄,the formation energy and transition energy level for each defect system,and further analyze their electronic structure and optical properties.The results show that the valence band and the conduction band of pure ZnGa₂O₄ primarily contributed from O2p,Zn 3d and Ga 3d and 4s.Its narrow stable thermodynamical region with wide variation range can adjust the concentration of most defects to a large extent,among which intrinsic defects V_O,Ga_Zn,Zn_Ga and V_Zn play an important role in the ZnGa₂O₄ defect system.The calculated defect levels of V_O,Ga_Zn,Zn_Ga and V_Zn are in the gap,in line with the electronic density and optical properties.Finally,we combine the theoretical and related experimental results to simulate the self-activated luminescence process of ZnGa₂O₄.In the fourth chapter,we find that in the Mn-poor environment,Mn can be doped into the tetrahedron or octahedral position with the change of?_O;while in the Mn-rich environment,Mn mainly enters the tetrahedral position.Then,in the ZnGa₂O₄ system with Zn_Ga,Mn²⁺is more likely to replace the Zn²⁺into the octahedral position of ZnGa₂O₄.According to the binding energy of the complex defects,it is found that the donor defect is not easy to combine with Mn_tet,and the acceptor defects V_Zn and Zn_Ga will obviously distort[MnO₄]tetrahedron,meaning that the acceptor defect does have an influence on the luminescence center of Mn²⁺.Finally,the impact of crystal field to the process of electron transition between the 3d energy levels with luminescence is simulated,based on the electronic structure of ZnGa₂O₄:Mn and complex defects,as well as the experimental near-infrared luminescence observed in ZnGa₂O₄:Mn sample.In this paper,we emphasize that intrinsic defects play an vital role on doping mechanism and the luminescence property of ZnGa₂O₄:Mn.We combine the self-activated luminescence process and the luminescence process of Mn²⁺to simulate intrinsic defects how to affect the long persistence mechanism of ZnGa₂O₄:Mn.