Electron Trap Depths in Cubic Lutetium Oxide Doped with Pr and Ti, Zr or HfRFrom Ab Initio Multiconfigurational Calculations

We propose a universalapproach to model intervalencecharge transfer(IVCT) and metal-to-metal charge transfer (MMCT) transitions betweenions in solids. The approach relies on already well-known and reliableab initio RASSCF/CASPT2/RASSI-SO calculations for a series of emissioncenter coordination geometries (restricted active space self-consistentfield, complete active space second-order perturbation theory, andrestricted active space state interaction with spin-orbit coupling).Embedding with ab initio model potentials (AIMPs) is used to representthe crystal lattice. We propose a way to construct the geometriesvia interpolation of the coordinates obtained using solid-state densityfunctional theory (DFT) calculations for the structures where theactivator metal is at specific oxidation (charge) states of interest.The approach thus takes the best of two worlds: the precision of theembedded cluster calculations (including localized excited states)and the geometries from DFT, where the effects of ionic radii mismatch(and eventual nearby defects) can be modeled explicitly. The methodis applied to the Pr activator and Ti, Zr, Hf codopants in cubic Lu2O3, in which the said ions are used to obtain energystorage and thermoluminescence properties. Electron trap chargingand discharging mechanisms (not involving a conduction band) are discussedin the context of the IVCT and MMCT role in them. Trap depths andtrap quenching pathways are analyzed.