Jahn–Teller and Non-Jahn–Teller Systems Involving CuF64– Units: Role of the Internal Electric Field in Ba2ZnF6:Cu2+ and Other Insulating Systems

Abstract

The applicability of the Jahn–Teller (JT) framework to 6-fold coordinated d9 ions whose local symmetry is not strictly octahedral is explored by means of first principle calculations. Our results contradict much of the existing literature where these systems are analyzed within the quasi-JT regime which assumes the usual JT description with a small splitting between b1g(∼x2–y2) and a1g(∼3z2–r2) orbitals and also the existence of three nearly equivalent distortions. To clarify this issue we investigate the equilibrium geometry (equatorial, Req, and axial, Rax, Cu2+–F– distances) and optical transitions for CuF64– units formed in Cu2+-doped the tetragonal Ba2ZnF6 host lattice. While the experimental d–d transitions cannot be reproduced through the isolated CuF64– unit at the equilibrium geometry, a reasonable agreement is reached adding in the calculation the internal electric field, ER(r), created by the rest of lattice ions on the electrons confined in the complex. It is shown that this tetragonal field, ...