Phosphatidylcholine vesicles provide reaction compartments for the synthesis of nanometer-size CdS, ZnyCd1-yS, and HgyCd1-yS particles with size- and composition-tunable absorbance and luminescence features. Spectrophotometric and spectrofluorimetric measurements are consistent with crystalline, monodisperse particles with few core or surface defects and uniform core composition Core-shell. CdS-HgS and CdS-ZnS nanocrystals also are synthesized within the vesicle interiors by alternating addition of cations and sulfide to build layered particles. These materials exhibit well-defined, yet qualitatively different, absorbance and luminescence spectra and establish the versatility of vesicles for synthesis of both mixed and layered composition nanocrystals.