Determination of 4f energy levels for trivalent lanthanide ions in YAlO3 by X-ray photoelectron spectroscopy

A simple method to analyze 4f energy levels of trivalent lanthanide (Ln) ions was demonstrated by conventional X-ray photoelectron spectroscopy (XPS) measurements using Ln ions doped YAlO3 sintered polycrystalline samples. Although XPS peaks derived from Ln 4f states overlapped with the host's valence band consisting of O 2p states, the difference XPS spectra between Ln doped and non-doped samples showed only the Ln 4f peaks due to the large difference of photoionization cross sections between Ln 4f and O 2p orbitals. The difference spectra showing Ln 4f states were aligned at the valence band maximum (VBM) making use of the peaks of Al 2p inner shells, and the Ln3 + 4f energy levels referred to the VBM were determined from the Ln3 + 4f peak energies. The Ln3 + 4f energy levels obtained by this simple method were in good agreement with those previously obtained by resonant ultraviolet photoelectron spectroscopy measurements using single crystal samples.