Ultraviolet and X-ray photoelectron spectra and the electronic structure of Eu(III) and Lu(III) β-diketonate complexes

Abstract

A. V. Shurygin, V. V. Korochentsev, I. S. Os'mushko, A. I. Cherednichenko, V. A. Yashin, and V. I. Vovna UDC 539.194 Ultraviolet (UV) and X-ray photoelectron spectroscopy and quantum chemistry methods (DFT) are used to study tris-β-diketonates of the rare-earth metals europium and lutetium. New information is obtained on the electronic structure of the complexes. The geometric and electronic structures of the compounds are calculated. The nature of chemical bonding in the compounds is analyzed. The quantum-chemical studies reveal patterns in the variations of the electronic structure, which depend on the complexing agent, and determine the effects of the substitution of C(CН) 3 and CF 3 for CН 3 -groups in the ligands. Band identification is obtained for the UV (in the gaseous phase) and X-ray photoelectron (in the condensed state) spectra of Eu and Lu tris-dibenzoylmetanates.Chelate complexes of trivalent lanthanide ions with β-diketonate ligands are increasingly used in various fields of science and technology, such as light-conversion materials and luminophores, in optoelectronics, in light sources, etc. [1-7]. The quantum yield of luminescence in the visible and near infrared regions is in large part dependent on the ligands and may vary by two to three orders of magnitude, depending on the effectiveness of radiationless transitions from the ligands to the metal. The excitation energy transfer processes depend, firstly, on the energy range between the lowest triplet state of the ligands and the excited state of f electrons and, secondly, on the localization of excitation on the functional groups of the ligands. Studies on the relationship between the complexes' spectral and luminescent properties and their electronic structure and the orbital nature of chemical bonds allow researchers to plan the synthesis of new compounds with the desired optical properties.The most informative methods in the study of the electronic structure of chemical compounds are UV photoelectron spectroscopy (UPS) of vapors, X-ray photoelectron spectroscopy (XPS) of the condensed phase, and X-ray emission spectroscopy combined with quantum chemical calculations [8][9][10][11]. There are few UPS studies of vapors of tris-β-diketonate lanthanide complexes. The possibilities of studying the UV photoelectron spectra of vapors of tris-acetylacetonates Ln(Асас) 3 and other coordination-nonsaturated complexes with diketonate ligands is limited by the possibilities of their conversion into the gaseous phase without visible destruction. Recently, a brief communication [12] was published on a He(I)