Quantum dots each having a core-shell structure which can be realized to have Type I structure in a ZnTe core. The quantum dots are cadmium-free core-shall structured quantum dots, in which the core contains Zn and Te and the shell contains Mg and S. The quantum dots may be structured with (a core containing Zn and Te)/MgS, (a core containing Zn and Te)/MgS, (a core containing Zn and Te)/ZnMgS/MgS, (a core containing Zn and Te)/MgS/ZnS, (a core containing Zn and Te)/ZnMgS/MgS/ZnS, (a core containing Zn and Te)/MgS/ZnO, or (a core containing Zn and Te)/ZnMgS/MgS/ZnO.