Theoretical Study On Electron Paramagnetic Resonance(EPR)Properties Of D~9 Ions Under Low Symmetries

The novel function materials represent a fast growing set of advanced materials containing unique mechanical,thermal,electrical,optical and magnetic properties,which are widely applied in various fields such as ceramics,alloys,electronic devices and polymers.Transition-metal ions are often doped in functional materials due to their important optical and magnetic properties arising from the abundant electronic levels of the unfilled d shells.These properties usually strongly depend on the local structures and electronic states around the transition-metal dopants and can be efficiently studied by means of the important spectroscopic technique-electron paramagnetic resonance(EPR).This thesis deals mainly with the EPR features of the representative d⁹ ions among the transition-metal groups by using the perturbation formulas of the spin Hamiltonian parameters(SHPs)for these ions under low(tetragonal and orthorhombic or rhombic)symmetries.Based on the calculations,the experimental SHPs are satisfactorily explained,and the information of the local structures around these d⁹ ions is acquired.Further,the relationship between the local structures of the dopants and SHPs(especially anisotropies)as well as the related physical mechanisms are discussed.In addition,the experimental researches on the wide-gamut blended microspheres of fluorescent conjugated polymers(CPs)are also illustrated.The main results are listed as follows.(1)The SHPs for 3d⁹transition ions(Cu²⁺,Ni⁺)under low symmetries are investigated.First,the anisotropic g factors of the deoxygenated YBaCuO(Y123)are theoretically studied using the perturbation formulas of the g factors for a tetragonally elongated octahedral 3d⁹ cluster.The g anisotropy is ascribed to the local tetragonal elongation of this copper site,characterized by one longer axial copper-apical oxygen bond and four shorter coplanar ones.The ligand orbital and spin-orbit coupling contributions are included from the cluster approach in view of covalency.The calculated g factors show good agreement with the experimental data.Second,the SHPs and local structures are theoretically studied for Cu²⁺in alkali borate Li₂O-B₂O₃(LB)and Na₂O-B₂O₃(NB)glasses by the high order perturbation calculations of these parameters for tetragonally elongated octahedral 3d⁹ clusters.The octahedral[CuO₆]^10?clusters are found to undergo the relative tetragonal elongations of about 12.8%and 9.2%for LB and NB glasses,respectively,arising from the Jahn-Teller effect.The local structures and SHPs are theoretically studied for Cu²⁺in alkali barium borate glasses 20A₂CO₃?24.5Ba CO₃·55H₃BO₃·0.5Cu CO₃(ABB,where A=Li,Na and K)by the quantitative calculations of these parameters for tetragonally elongated octahedral 3d⁹ clusters.The[CuO₆]^10?clusters are subject to the local relative tetragonal elongation ratios 7.8%,8.1%and 8.4%in Li BB,Na BB and KBB glasses,respectively,owing to the Jahn-Teller effect.Theoretical and experimental SHPs show reasonable agreement.Third,the SHPs,local structures and the concentration dependences for Ni⁺in the mixed Rb_1-xCs_xCa F₃ crystal are theoretically investigated from the perturbation formulas of these parameters for a tetragonally elongated octahedral 3d⁹ group.Due to the Jahn-Teller effect,the[Ni F6]^10?clusters are found to experience the moderate tetragonal elongation distortions along C₄ axis,which is characterized by the moderate relative tetragonal elongation(35)Z and the other parameters(the corresponding cation–anion distance R_H in the pure crystal,covalency factor N,the proportionality factor?and the cubic field parameter D_q)that follows the linear relationship as the increasing of concentration for the studied system.Finally,the local structure and SHPs(g factors and hyperfine structure constants)of[CuO₂N₂]^8-cluster in Cu²⁺complexes with Schiff base DMIIMP are calculated using ORCA software.The obtained results agree well with the XRD and EPR experimental findings.The calculated SHPs are also compared with the results based on the perturbation formulas of the SHPs for tetragonally elongated octahedral 3d9 clusters.The electron paramagnetic resonance(EPR)parameters(g factors and hyperfine structure constants)for Cu²⁺in[Zn(mein)₂(H₂O)₄]?(sac)₂ complex are theoretically investigated from the high order perturbation formulas of these parameters for a 3d⁹ ion in a rhombically elongated octahedron.The results show good consistency with that obtained from the DFT method.It illustrates the cluster model and uniform perturbation formulas apply to this kind of system.(2)The high-order perturbation formulas of SHPs are applied to analyze the SHPs and local distortions for 4d⁹(Ag²⁺)in a tetragonally elongated octahedron.First,the SHPs for Ag²⁺in NaF and CsCdF₃ crystals are theoretically investigated by including the contributions from the charge transfer mechanism.By employing the fewer adjustable parameters,the calculated SHPs based on the above uniform formulas and the local tetragonal elongations agree well with the experimental data.The impurity centers are found to undergo the relative tetragonal elongation ratios of about 9.4%and8.2%for Ag²⁺in NaF and CsCdF₃,respectively,along the C₄ axis due to the Jahn-Teller effect.Then the SHPs and local structures for Ag²⁺in Ag Cl and KCl are theoretically studied by using the perturbation formulas of these parameters.The impurity centers are found to suffer the relative elongations(?0.05 and 0.21?for Ag²⁺in Ag Cl and KCl,respectively)along the C₄ axis because of the Jahn-Teller effect.The increasing tetragonal elongations from Ag Cl to KCl are attributed to the weaker chemical bonding(or lower force constant)in the latter.(3)The defect structure around Au²⁺in ZnSe crystal is theoretically studied by analyzing its SHPs based on the perturbation formulas of SHPs for 5d⁹(Au²⁺)in a tetragonally elongated octahedron.The ligand orbital and spin-orbit coupling contributions are included from the cluster approach because of significant covalency of the system.The impurity Au²⁺is found to occupy the octahedral interstitial site and exhibits the tetragonal elongation distortion of about 8.4%due to the Jahn-Teller effect.(4)An ultrabright alternative to conventional fluorescent microsphere technologies is introduced.The fluorescent conjugated polymers MEH-PPP,EH-P(PVPVP)and MEH-PPV with three typical colors(blue,green and red)are synthesized and found to show widely separated Commission Internationale de L'Eclairage(CIE)color coordinates.Through appropriate mixtures of the above fluorescent CPs,the new method of blended fluorescent microsphere is proposed with well-defined domain structures and an extensive range of color coordinates including white.