Crystal-field spectra of d3,7 ions. V. Tetrahedral CO 2+ in ZnAl2O4 Spinel

Abstract

Absorption and fluorescence spectra of Co2+ in the tetrahedral (Td) site of ZnAl2O4 spinel (gahnite) at low temperatures have been observed and analyzed. The resulting energy-level diagram includes four quartet states and nine doublets, and has been interpreted first in terms of a weak field formalism without spin-orbit coupling. In this analysis the "free-ion" levels for Dq = 0 were deduced and compared with those for a free ion outside the influence of the crystalline environment. The reduction in the electrostatic interaction parameters F2 and Ft in the crystal is due to the effect of covalency. A second approach has been used to analyze the fine structure of the energy levels in terms of a strong field spin-orbit formalism. The fine structure can be explained for all the bands on the basis of simple spin-orbit splitting, but the possibility of a JahnTeller distortion of the 4T1a state cannot be entirely eliminated.