Photoluminescence from a Gem–Sin–Gemstructure has recently been demonstrated at room temperature by Gailetal. [Appl. Phys. Lett.66, 2978 (1995)]. Experimental measurements have shown that this luminescence is associated with the fourfold degenerate conduction minima which lie in the plane of the interface. In this letter, we report full‐scale microscopic calculations on both perfect and imperfect structures of this type which demonstrate that these results cannot be explained either by a ‘‘zone‐folding’’ or an alloy scattering model. We propose an alternative mechanism which links the luminescence to anomalous localization at the heterointerfaces. ©1996 American Institute of Physics.