photoluminescence and raman investigations of selected alloy semiconductor epilayers are reported. correlations relating optical spectra and a number of intrinsic and extrinsic properties of the materials studied are found. of particular interest, preliminary measurements on a promising new quaternary system (ingaalas/inp) are reported and mixed mode alas-like lo raman scattering processes in this material are identified for the first time. in addition, evidence for defect related photoluminescence associated with the energy gap region in cdte is also reported.