Importance of Fourth-Order Zero-Field Splitting Terms in Random-Orientation EPR Spectra of Eu(II)-Doped Strontium Aluminate

Abstract

This work discusses an issue caused by omitting the fourth-order zero-field splitting (ZFS) terms in the analysis of random-orientation EPR spectra. Eu(II)-doped strontium aluminates were employed as a model system of the S-state lanthanoid ions, which have relatively large second-rank ZFS components, comparable to the conventional X-band microwave energy. The initial estimation of second-and fourth-rank ZFS components was acquired uniquely from the W-band spectrum based on a perturbation treatment of the spin Hamiltonian, and they were refined by a hybrid-eigenfield simulation approach. A parallel simulation of the X-and W-band spectra with the refined parameters reasonably reproduced both the observed spectra. The reliability of the parameters was also verified by reproducing the off-principal-axis extra lines arising from the M S ) 1/2 T -1/2 transition observed in the W-band spectrum. By comparison with an analysis based on the spin Hamiltonian omitting the fourth-order terms, it was concluded that omitting these terms results in an erroneous determination of the rhombic parameter (E) of the second-rank ZFS tensor. The obtained reliable secondrank ZFS tensors enabled us to invoke the superposition model, determining their principal-axis orientation. This is the first report of such relative orientation determined for Eu(II)-doped strontium aluminates.

g-Anisotropy of the S2-State Manganese Cluster in Single Crystals of Cyanobacterial Photosystem II Studied by W-Band Electron Paramagnetic Resonance Spectroscopy

“…It should be noted that there is a remarkable difference between the g -tensors determined in this work and those in ref . We also evaluated the g -tensor by spectral simulation with the help of a least-squares fitting procedure described previously, where the g -tensor in ref was employed as the initial parameter of the fitting procedure. Figures a and b show the best-fit simulation obtained from the spectral analysis.…”

“…Electron Paramagnetic Resonance Spectral Simulation. Computer simulation of EPR spectra was carried out by a modified program based on second-order perturbation theory, which was constructed using MATLAB 6.5 provided by MathWorks, Inc. 34 In the program, resonance fields and transition intensities were calculated with analytical expressions derived by Iwasaki. 33 Results and Discussion S 2 -State Multiline Signal in Single Crystals and Frozen Solutions of PSII.…”

Synthesis, luminescence and persistent luminescence of europium-doped strontium aluminates

“…It is important to note that due to the high zero-field strength, conventional X-band EPR spectra for Eu 2+ in SA give a second order spectrum with many bands between 0.03 and 0.5 T [262] which cannot be assigned without the full diagonalization of the spin Hamiltonian. Fourth-order spin Hamiltonian parameters were obtained for Eu 2+ in a mixture of 5:1 mixture of SA and S4A7 powders [263]. The spectra showed two pairs of centers with relative intensity 5:1, confirming that the two different Sr sites in both hosts are equally substituted with Eu 2+ .…”

Time-Resolved Electron Paramagnetic Resonance and Theoretical Investigations of Metal-Free Room-Temperature Triplet Emitters

“…Computer simulation of EPR spectra was carried out by a homemade program, which was constructed using MATLAB 2012b from The MathWorks, Inc. In this program, resonance fields and transition intensities were calculated using a hybrid-eigenfield approach, which has been proposed as a practical method for EPR spectral simulation. ,− In the simulation, resonance fields are calculated directly without any iteration procedure, based on the eigenfield method originally developed by Belford et al Transition probabilities are calculated by diagonalizing the eigen-energy matrix with the obtained resonance fields.…”