The refractive indices ofCd1−xMnxTeandCd1−yMgyTe(0<x<0.28and0<y<0.70) were determined by analyzing interference fringes in reflectivity spectra of thin films grown by molecular beam epitaxy. It is shown that their dispersions in the transparent region at 4 K are well described by a Sellmeier relation. These results have been applied to grow CdMnTe/CdMgTe Bragg mirrors incorporated in a II–VI microcavity operating in the strong exciton-photon coupling regime. ©1997 American Institute of Physics.