Electronic Properties And4fâ†'5d Transitions In Ce-doped Lu₂SiO₅: A Theoretical Investigation

Rare earth elements due to their unique electronic configurationsexhibit excellent optical, electrical and magnetic properties, and thus theirapplications in modern science and technology have attracted more andmore attention. Among those applications, rare earth luminescentmaterials have become an important part of modern optical materials. Inrecent years, the focus is on the study of a variety of luminescentproperties of the rare earth doped crystals. As the development ofcomputer technology, computational physics, experimental physics andtheoretical physics have become the three major branches of physics.First-principles calculations are gradually becoming an importantresearch tool in physics, chemistry and other fields. In this article, wehave performed some studies on rare earth doped luminescent materialsby means of calculations and simulations with the density functionaltheory using high-performance computer clusters.The thesis is organized as follows:The first chapter mainly introduces the properties of rare earthelements and their applications in the modern science and technology, aswell as those of rare earth luminescent materials and their applications. Atthe end of this chapter, we also introduce the basic concepts and thedevelopment of first-principles. The second chapter describes the general framework of theHartree-Fock theory and density functional theory. Moreover, at the endof this chapter the computational softwares VASP and MOLCAS is alsointroduced brieflyThe third chapter is the main body of this thesis. We have studied theelectronic properties and4fâ†'5d transitions of Ce-doped Lu₂SiO₅（LSO）using the hybrid DFT calculations with the periodic supercell model andthe wavefunction-based CASSCF/CASPT2calculations with theembedded cluster model, respectively. Firstly, the structure of theundoped and Ce-doped Lu₂SiO₅was first optimized using the standardDFT-PBE method. After that, we use PBE and HSE06functional to studythe electronic property of the optimized crystal. Using the relaxed atomicstructures of CeLu1-and CeLu2-doped Lu₂SiO₅supercells, we constructedthe Ce-centered embedded clusters (Ce_Lu1O₇Si₄)⁵⁺and （CeLu2O6Si4）7+, andperform CASSCF/CASPT2calculations to investigate the4fâ†'5dtransitions. From comparisons of the calculated and experimentaltransition energies, the two different types of4fâ†'5d excitation bands asobserved experimentally have been identified as due to the Ce³⁺ionslocated in the two substitutional Lu sites. Finally, the changes of the twolowest4fâ†'5d transition energies from CeLu1to CeLu2have been analyzedin terms of the centroid-energy difference and the crystal-field splitting of5d1configuration.