We report the molecular beam epitaxialgrowth and photoluminescence of Si1-xGex/Si alloy-based 'naked' quantum wells (QWs). The PL stability and anomalous spectral modulation characteristic of naked QWs are discussed in the context of surface morphological change. Experimental findings as well as theoretical calculations suggest that the in-plane exciton localization rather than perpendicular confinement due to the surface barrier dominates the PL mechanism of naked QWs.