Oxidation state sensitivity of Eu Lγ₄ emission and its applications to oxidation state selective EXAFS spectroscopy of EuPd ₂Si₂

In this paper, we have examined analytical spectrometry using Eu Lγ₄. The oxidation-state-fluctuating compound EuPd ₂Si₂ exhibits the largest temperature-induced valence changes among all Eu systems and does not have a structural phase transition below 298 K; EuPd₂Si₂ has a precipitous valence transition near 150 K. Hence, high-resolution Eu Lγ₄ emission spectra of EuPd₂Si₂ at 298 K and 30 K were measured using a multicrystal multidetector spectrometer. The spectra exhibited substantial differences, thereby indicating that the spectral shapes of Eu Lγ₄ emissions depend on the oxidation state of the Eu ions. We have also demonstrated the applicability of Eu Lγ₄ emission to oxidation state selective extended X-ray absorption fine structure (EXAFS) spectroscopy through partial fluorescence yield measurements with an excitation energy range of approximately 0.5 keV. In this manner, we have addressed and resolved two key questions in analytical spectrometry using Eu Lγ₄.