Optical absorption and ESR studies of nickel ions in sodium zinc sulphate tetrahydrate

The optical absorption spectrum of Ni doped Na2Zn(SO4)2 · 4 H2O shows that nickel enters the lattice in its divalent state. ESR spectra of X‐irradiated sample show two doublets corresponding to the two sites of the unit cell. The spectra are fitted to a spin‐Hamiltonian of orthorhombic symmetry and the doublet structure is found to be due to a superhyperfine interaction with a proton. A correlation of the ESR results and observed changes in optical absorption spectra after irradiation indicates the formation of Ni3+. Possible mechanisms responsible for the observed proton hyperfine interaction are discussed. Copyright © 1978 WILEY‐VCH Verlag GmbH & Co. KGaA