  Samarium has two stable valence states, 2+ and 3+, which coexist in many
compounds forming spatially homogeneous intermediate valence states. We study
the valence state of samarium when incorporated in a single crystalline EuO
thin film which crystallizes in a $fcc$-structure similar to that of the
intermediate valence SmO, but with a larger lattice constant. Due to the
increased lattice spacing, a stabilization of the larger Sm$^{2+}$ ion is
expected. Surprisingly, the samarium incorporated in
Sm$_{\mathrm{x}}$Eu$_{\mathrm{1-x}}$O thin films shows a predominantly
trivalent character, as determined by x-ray photoelectron spectroscopy and
magnetometry measurements. We infer that the O$^{2-}$ ions in the EuO lattice
have enough room to move locally, so as to reduce the Sm-O distance and
stabilize the Sm$^{3+}$ valence.
