  We study the electronic structure of Tsai-type cluster-based quasicrystalline
approximants, Au$_{64}$Ge$_{22}$Yb$_{14}$ (AGY-I),
Au$_{63.5}$Ge$_{20.5}$Yb$_{16}$ (AGY-II), and Zn$_{85.4}$Yb$_{14.6}$ (Zn-Yb),
by means of photoemission spectroscopy. In the valence band hard x-ray
photoemission spectra of AGY-II and Zn-Yb, we separately observe a fully
occupied Yb 4$f$ state and a valence fluctuation derived Kondo resonance peak,
reflecting two inequivalent Yb sites, a single Yb atom in the cluster center
and its surrounding Yb icosahedron, respectively. The fully occupied 4$f$
signal is absent in AGY-I containing no Yb atom in the cluster center. The
results provide direct evidence for a heterogeneous valence state in AGY-II and
Zn-Yb.
