Electronic structure studies of V6O13 by soft x-ray emission spectroscopy:: Band-like and excitonic vanadium states -: art. no. 125103

Resonant soft x-ray emission (SXE) spectra of the mixed valence vanadium oxide V6O13 have been recorded for a series of excitation energies across the V L-absorption band. Resonant excitation allows one to distinguish between charge neutral low-energy excitations and continuum-excited, more band-like V 3d valence band states in the spectra. We find that the V L-emission spectra of V6O13 consist of two distinct components that can be assigned to nearly pure V 3d states, and to V 3d states that are strongly hybridized with O 2p states, respectively. Band structure calculations of the density functional theory support the assignment of these features. At threshold excitation the V L-emission spectra of V6O13 show strong signatures from excitonic states, the energy dependence of which shows Raman-like behavior. We compare these spectral features in the resonant SXE spectra with cluster model calculations and assign them to dd excitations and charge-transfer excitations, respectively. Finally, we discuss changes in the V L-absorption and emission spectra that take place when changing the sample temperature from 295 K to 120 K. We relate the changes to redistributions in the V 3d partial density of states, which occur at the transition temperature for the metal-semiconductor-transition T-MST = 150 K and find support in our temperature dependent band structure calculations.