Studies of the EPR parameters and defect structure for tetrahedral Fe³⁺ centers in zinc oxide

Abstract

The relations between the electron paramagnetic resonance (EPR) parameters and crystal structure of Fe3+:ZnO crystals have been established. On the basis of this, the EPR parameters D, (a‐F) and the zero‐field splitting (ZFS) δ1, δ2 of the ground state for Fe3+ in Fe3+:ZnO crystals are theoretically investigated using the complete diagonalization method (CDM). The theoretical second‐order EPR parameter D, the fourth‐order EPR parameter (a‐F), and the ZFS of the ground state: δ1, δ2 for Fe3+ in Fe3+:ZnO yield a good agreement with experimental findings when the three O2– ions below the Fe3+ ion rotate by Δθ in the range 0.475–0.562° away from the [111] axis. Hence, the local structure distortion effect plays an important role in explaining the spectroscopic properties of Fe3+ ions in Fe3+:ZnO crystals. Our approach takes into account the spin–orbit (SO) interaction as well as the spin–spin (SS), spin–other–orbit (SOO), and orbit–orbit (OO) interactions omitted in previous studies. This shows that although the SO interaction is the most important one, the contributions to the EPR parameters from the other three interactions are appreciable and should not be omitted, especially for the EPR parameter D. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Local coordination of Fe3+in ZnO nanoparticles: multi-frequency electron paramagnetic resonance (EPR) and Newman superposition model analysis

“…The positive/negative sign in ΔR corresponds to an elongation/compression in the ligands' distances, whereas those in Δθ correspond to an increase/decrease in θ, respectively. The same system was previously studied by Li et al [22] and independently by Yang [23] by applying a different theoretical method based on diagonalizing the complete energy matrices. ΔR = -0.0119 nm (for both R 1 and R 2 ) and Δθ = 0.339 o were obtained by Li et al [22], and a Δθ of only 0.475°-0.562° by Yang [23] with respect to the experimental findings [52].…”

“…The same system was previously studied by Li et al [22] and independently by Yang [23] by applying a different theoretical method based on diagonalizing the complete energy matrices. ΔR = -0.0119 nm (for both R 1 and R 2 ) and Δθ = 0.339 o were obtained by Li et al [22], and a Δθ of only 0.475°-0.562° by Yang [23] with respect to the experimental findings [52]. These values describe considerably stronger distortions for the ligand distances with respect to the ones (from both A(+) and A(-)) determined here, and an increase in θ similar to that of A(+).…”

“…to kill certain human cancer cells [21]. Numerous theoretical studies, which are mainly focused on the defect structure of tetrahedral Fe 3+ centers, also exist [22][23][24]. However, due to insufficient analytical characterization of the materials and the lack of data from advanced electron paramagnetic resonance (EPR) techniques, which precludes the unambiguous determination of spin-Hamiltonian parameters for Fe 3+ incorporated into ZnO, the local position of Fe 3+ in the ZnO lattice and the sign of the zero-field splitting (ZFS) parameters remain unclear and are still a matter of debate [12-14, 19, 20, 22-25].…”