Polarized electronic spectra of tetrahedral nickel(II) ions in a Cs 2ZnCl 4 host lattice at temperatures between 300 and 10 K

Abstract

The polarized visible spectra of tetrahedral nickel(II) ions in a Cs 2ZnCl 4 lattice at temperatures between 300 and 10 K is reported. Cs 2ZnCl 4 is orthorhombic and the polarization results confirm that the electric dipole process is operative. The degree of distortion from tetrahedral symmetry of the NiCl 4 2− moiety along each principal axis of the crystal is a major factor in determining the intensity of the spectrum taken with the incident-beam polarization in that direction. The spectra are unusual in that the double peak characteristic of tetrahedral nickel at room temperature is retained at 10 K along the two crystallographic axes where the distortion from tetrahedral symmetry is most marked. In common with most previous studies of tetrahedral nickel spectra at low temperature, the spectrum taken at 10 K with the incident-beam polarization along the third axis produces a quite different spectrum than at room temperature. The change occurs gradually between 200 and 100 K. A qualitative model to explain these observations based on the concept that a dynamic Jahn-Teller effect is operative at room temperature is proposed.