Nonresonant valence-to-core x-ray emission spectroscopy of niobium

The valence-to-core (V2C) portion of x-ray emission spectroscopy (XES) measures the electron states close to the Fermi level. These states are involved in bonding, thus providing a measure of the chemistry of the material. In this article, we show the V2C XES spectra for several niobium compounds. The $K{\ensuremath{\beta}}^{\ensuremath{''}}$ peak in the V2C XES results from the transition of a ligand $2s$ electron into the $1s$ core-hole of the niobium, a transition allowed by hybridization with the niobium $4p$. This location in energy of this weak peak shows a strong ligand dependence, thus providing a sensitive probe of the ligand environment about the niobium.