A series of hexagonal mesoporous germanium semiconductors with tunable wall
thickness is reported. These materials exhibit systematically blue shifted
optical adsorption and strong room temperature photoluminescence properties
that depend on the thickness of the framework wall, a behavior which is
analogous to the blue shifted absorption in discrete nanocrystals.

From: G.S. Armatas, M.G. Kanatzidis, “Size Dependence in Hexagonal Mesoporous Germanium: Pore Wall Thickness versus Energy gap and Photoluminescence“,
Nano Lett. 10,
3330-3336 (2010).