THE COUPLING OF T-4(2) AND E-2 STATES OF THE CR-3+ ION IN SOLID-STATE MATERIALS

In this paper we present and discuss two different models describing the coupling of 2E and 4T2 states of octahedrally (or nearly octahedrally) coordinated Cr3+ ions. Both the electron-lattice interaction and spin-orbit coupling of the doublet and quartet states are taken into account. The electron-lattice interaction is scaled by experimentally measured Stokes shifts whereas the spin-orbit coupling is used as a fitting parameter (approximately 200 cm-1). The results are then compared to experimental data for Cr3+-doped garnets, and kyanite (Al2O3:SiO2). The agreement with experiment is much better for the model in which the spin-orbit interaction is first included in the electronic Hamiltonian with the lattice frozen at the point, characterizing the average lattice position in the vibronic state. In the case of kyanite different spin-orbit coupling constants (160 and 320 cm-1) have to be assigned to the split components of the 2E level, contrary to the case of weakly split systems.