EPR and optical spectra of Ni~(2+)-V_(Ag) in silver chloride and silver bromide

摘要

The optical absorption and EPR spectra of Ni~(2+)-V_(Ag) centres in the AgCl:Ni~(2+) and AgBr:Ni~(2+) systems have been investigated theoretically on the basis of the complete energy matrices including the electron-electron repulsion interaction, the ligand field interaction, the spin–orbit coupling interaction, and Zeeman interaction. Because the charge compensation forms a silver ion vacancy (V_(Ag)) which makes the attractive force acted on the each ligand ion different, it was determined that the Ni–X (X = Cl, Br) distance next to VAg is shorter than others for both AgCl:Ni~(2+) and AgBr:Ni~(2+) systems in the tetragonal symmetry. Besides, it was found that the local lattice structure of (NiX_6)~(4-) clusters in AgC1 and AgBr crystals exhibit a compression distortion. This compression distortion may be ascribed to the fact that the Ni~(2+) ion has a smaller ionic radius and more effective charge than the Ag~+ ion.