title: Configuration coordinate energy level diagrams of intervalence and metal-to-metal charge transfer states of dopant pairs in solids.
abstract: Configuration coordinate diagrams, which are normally used in a qualitative manner for the energy levels of active centers in phosphors, are quantitatively obtained here for intervalence charge transfer (IVCT) states of mixed valence pairs and metal-to-metal charge transfer (MMCT) states of heteronuclear pairs, in solid hosts. The procedure relies on vibrational frequencies and excitation energies of single-ion active centers, and on differences between ion-ligand distances of the donor and the acceptor, which are attainable empirically or through ab initio calculations. The configuration coordinate diagrams of the Yb(2+)/Yb(3+) mixed-valence pair in Yb-doped YAG and the Ce(3+)/Yb(3+) heteronuclear pair in Ce,Yb-codoped YAG, are obtained and described. They are drawn from empirical data of the single-ions and their usefulness is discussed. The first diagram suggests that IVCT states of Yb(2+)/Yb(3+) pairs may play an important role in the quenching of the Yb(3+) emission and it provides the details of the quenching mechanism. The second diagram supports the interpretation recently given for the energy transfer from Ce(3+) to Yb(3+) in Ce,Yb-codoped YAG via a MMCT Ce(4+)-Yb(2+) state and it provides the details. The analyses of the two diagrams suggest the formation of Yb(2+)/Yb(3+) pairs after the Ce(3+)-to-Yb(3+) MMCT, which is responsible for the temperature quenching of the Yb(3+) emission excited via Ce(3+) (4f → 5d) absorption in Ce,Yb-codoped YAG.
authors.affiliation: Departamento de Química, Universidad Autónoma de Madrid, 28049 Madrid, Spain. luis.seijo@uam.es.
authors.forename: Zoila
authors.initials: Z
authors.lastname: Barandiarán
authors.forename: Andries
authors.initials: A
authors.lastname: Meijerink
authors.forename: Luis
authors.initials: L
authors.lastname: Seijo
mesh_terms: D004579:Electron Transport; D007477:Ions / Q000737:chemistry; D008670:Metals / Q000737:chemistry*; D015018:Ytterbium / Q000737:chemistry
chemical_list: D007477:Ions; D008670:Metals; D015018:Ytterbium