Theoretical Investigations On The Spin Hamiltonian Parameters And Local Structures For V⁴⁺ In Borate Glasses

The optical and magnetic properties of functional materials such as optical glasses can be significantly modified when doped with transition-metal ions(e.g.,V⁴⁺)due to the abundant transitions between their unfilled 3d orbitals under the changes of local environments.The above local structural properties can be efficiently studied by means of UV-Vis absorption spectra and electron paramagnetic resonance（EPR）spectra.Importantly,the structures and properties can be conveniently modulated by changing the compositions of certain component and afford more extensive applications.So,the studies on the transition-metal ions in optical glasses are of special scientific significance.Among the family of optical glasses,borate glasses based on the former（network）B₂O₃ is one of the most important and widely studied systems.On the other hand,3d¹ ions(e.g.,V⁴⁺),as the typical configuration in the transition-metal group and the popular active impurities in optical glasses,have attracted extensive attention due to the relatively simpler energy level structures.The abundant researchers have been performed for V⁴⁺（3d¹）in borate glasses,with many experimental data for optical transitions and spin Hamiltonian parameters（i.e.,anisotropic g factors and hyperfine structure constants）in EPR spectra obtained,e.g.,the V⁴⁺centers in A₂CO₃·CaCO₃·H₃BO₃·V₂O₅（A=Li,Na,K）and TeO₂·Nb₂O₅·B₂O₃ glasses.However,the theoretical explanations to the above experimental results are relatively unsatisfactory.First,the experimental g factors were normally fitted by the simple second-order perturbation formulas of g factors with various adjustable bonding parameters in the previous treatments.Meanwhile,the analysis for the hyperfine structure constants was insufficient,sometimes without uniform quantitative explanations with g factors.Second,the above theoretical analysis on the spin Hamiltonian parameters failed to connect quantitatively with the local structures of the V⁴⁺impurities.And the information about the local structures of the impurities were not been obtained for these glass systems.Finally,the physical mechanisms for the concentration dependences of the spin Hamiltonian parameters have not been systematically discussed by involving these spectroscopic parameters and the local structures around the impurities.In order to overcome the above imperfections in the previous studies,in this thesis,systematic studies are carried out for the spin Hamiltonian parameters and local structures for V⁴⁺in TeO₂·Nb₂O₅·B₂O₃ and A₂CO₃·CaCO₃·H₃BO₃·V₂O₅（A=Li,Na and K）glasses.Based on the perturbation formulas of the spin Hamiltonian parameters for tetragonally compressed octahedral 3d¹ clusters,the quantitative relationships between the relevant parameters（such as molecular orbital coefficients and crystal field parameters,etc.）and the covalency and the local structures of the systems,and the experimental spin Hamiltonian parameters are satisfactorily interpreted,with the information of the local structures of the impurity ions determined.Meanwhile,the concentration dependences of the spin Hamiltonian parameters and local structures as well as their physical mechanisms are also analyzed for tetravalent vanadium impurities in these glasses.