A new method for determining the valence of lanthanide compounds: Lγ4 emission spectroscopy

Abstract

We have examined the potential of Lγ₄ emission spectroscopy as a new method for valence determination. Sm Lγ₄ emission spectra of a mixed valence compound, SmB₆, as well as Sm standard references were recorded using a multicrystal, multidetector spectrometer at 298 K. The Lγ₄ spectra exhibited a large chemical shift (∼4.5 eV) and substantial profile changes depending on the Sm oxidation state. Splitting of the Sm Lγ₄ band was attributed to spin-dependent atomic multiplets, and valence-dependent edge-shifts of the Sm L_I XANES spectra strongly suggest that the chemical shift of the Lγ₄ emission is mainly due to the screening effects of the Sm L_I core. The Lγ₄ spectrum of SmB₆ was well reproduced by the averaged spectra of SmS and SmF₃, indicating a SmB₆ valence of 2.65 ± 0.03. The advantages of the Lγ₄ method, including simple data treatment and no need for an excitation energy scan, will encourage its use in several areas of materials science.