In this presentation, we suggest a design principle for bright and robust heavy metal-free quantum dots (QDs). Specifically, we propose a InP emissive core/ZnSexS1-x/ZnS heterostructure and conduct a comprehensive study across synthesis, spectroscopy and calculation. The experimental results attest that the presence of Se near the InP core facilitates a uniform shell growth and S-rich outermost shell enables the decoupling of the electron wavefunction from the surface trap states. Bright, robust and color-pure InP/ZnSexS1-x/ZnS QDs, which meet the requirements of light-emitting applications, have been realized via engineering the composition profile of thick ZnSexS1-x shell. In addition, we also propose ternary III-V semiconductor nanocrystals, In1-y(GaxAl1-x)yP. With sophisticated engineering of the size and composition of the alloyed QDs, the key characteristics (i.e., lattice parameter, optical band gap and energy band position) can be controlled.