Optical Absorption Spectra of Ni-Doped Oxide Systems. I

The optical absorption was studied at room temperature, at 78°, and at 4.2°K in the 2.6-μ to 0.2-μ region in single crystals of MgO, ZnO, MgAl2O4, and yttrium-gallium garnet doped with nickel. The absorptions found were correlated to electronic transitions within the 3d-shell using the formalism of the crystal-field theory. The value of the Dq and B parameters were derived for MgO:Ni (Dq = — 815 cm—1; B = 890 cm—1) and for ZnO:Ni where Ni is tetrahedrally coordinated (Dq = 405 cm—1; B = 795 cm—1). Interesting fine structure was found in the absorption spectra of MgO:Ni and its implications are discussed. An attempt is made to explain some of the fine structure of the absorptions in MgO and ZnO as due to spin-orbit effects. The observed spectra for MgO:Ni are used to infer the presence of Ni++ in octahedral coordination, both in the spinel and in the green phase of yttrium gallium garnet.