Electronic absorption spectra ofCu2+inMgO:Ab initiotheory and experiment

Abstract

Ab initio model potential embedded cluster calculations on ${({\mathrm{CuO}}_{6})}^{10\ensuremath{-}}$ units were used to model the electronic absorption spectra of ${\mathrm{Cu}}^{2+}$ doped $\mathrm{MgO}$ single crystals. These theoretical results were compared with optical absorption spectra determined experimentally. The major interactions present in the system, including intracluster electron correlation and scalar relativistic effects, were incorporated, providing a good description of both ground and excited states. The first step in calculating the electronic spectrum was to optimize the geometry of the cluster by taking into account the distortion produced by the Jahn-Teller effect. As a result a ${\mathrm{D}}_{4h}$ geometry was obtained, which is associated with a compression of the original octahedron along the $z$ axis. Comparison of this geometry with extended x-ray absorption fine structure measurements is satisfactory. In clusters with ${\mathrm{D}}_{4h}$ geometry, vertical absorptions were calculated for $d$-$d$ transitions as well as for ligand-to-metal charge transfer transitions. Optical absorption measurements showed two broad absorption bands at about 4.5 and $5.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, which are attributed to charge-transfer transitions from the main ligand $2p$ ${t}_{1u}$ $\ensuremath{\sigma}$ and $\ensuremath{\pi}$ molecular orbitals to the metal $3d$ shell.