CdSe nanocrystals are now known as highly efficient fluorescent light sources. Their
efficiency is however strongly dependent on the quality of the passivation layers. We show
here that using a ZnSe/ZnS bi-layer shell leads to a larger photoluminescence yield than
both ZnSe and ZnS simple shells. The intermediate ZnSe layer acts as a lattice parameter
adaptation layer to improve on the core/shell interface quality, while the ZnS outer shell
maximizes the exciton confinement.