This work describes the optical material properties of SiGe/Si multi-layers that are epitaxially grown to define the channel material of CFET devices. Two sets of epitaxial growth conditions are compared. The absence/presence of lattice defects is verified by room temperature photoluminescence measurements. Photoluminescence measurements at low temperatures are used to study band-to-band luminescence from individual sub-layers and to demonstrate the absence of non-radiative recombination center in the CFET stack.