Bulk sensitive spectroscopies were performed for mixed valent compounds EuNi 2 (Si 1Àx Ge x ) 2 as a function of x, and Eu-sesquioxide (Eu 2 O 3 ), using techniques of high-resolution partial-fluorescence yield (PFY) and resonant inelastic x-ray scattering (RIXS) at the Eu L 3 absorption edge. The evolution of mean-valency as a function of chemical composition x in EuNi 2 (Si 1Àx Ge x ) 2 shows a drastic change between x ¼ 0:5 and 0.7. The experimental results also show a small amount of mixed valency for the end members, i.e., x ¼ 1 and 0 samples are also mixed valent. Single-impurity Anderson model calculations show good agreement with the PFY and RIXS experimental results, and thus provide a consistent set of electronic structure parameters. The composition controlled drastic change in meanvalence between x ¼ 0:5 and 0.7 is derived from a large hybridization change, consistent with the Kondo volume collapse picture.

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