With different properties from their bulk materials and potential applications in various fields

semiconductor quantum dots have been researched for several decades.The studying follows three directions:preparing quantum dots of new materials

finding novel preparation method and building up complex heterostructures

such as core-shell structures

quantum dot quantum well structures and so on.Owing to the quantum confinement effect

the rate of radiative transition and the effectiveness of the excitation transfer in quantum dots may be bigger than those in bulk materials

but surface states usually act as luminescence killers.So researching and controlling the surface of quantum dots are important.Because of the good passivation of the shell

some core-shell quantum dots have displayed a quantum yield of 50%.The electronic properties of quantum dot quantum well may be controlled by tuning the thickness and the energetic structures of various layers.The luminescence with high efficiency may be obtained.ZnS has a cubic structure of blende-type very close to that of CdS and a large band gap compared to that of CdS.These are the basic conditions to form a quantum dot quantum well with ZnS and CdS.In this paper

ZnS/CdS/ZnS quantum dot quantum well was prepared by inverted micelles method and was characterized.Dioctylsulfosuccinate sodium salt(AOT)was used as surfactant.The size of the quantum dot quantum well was controlled by the water-to-surfactant mole ratio.The size distribution was narrow and the diameter of the quantum dot quantum well was about 4.5nm

which was consistent with the theoretical calculation.The optical properties were compared with those of core-shell ZnS/CdS quantum dot.Both emissions of the quantum dot quantum well and the core-shell structure were peaked at 515nm which can be attributed to the donor-acceptor recombination in CdS.The luminescence of quantum dot quantum well was stronger than that of the core-shell structure.This can be explained that the ZnS shell of the quantum dot quantum well increased the distance from CdS to surface states

reducing the nonradiative recombination rates.The luminescence decay was measured and the decay curves were fitted by a hyperbolic function.The results indicated that the ZnS shell reduced the relative contribution of the fast process to the overall emission.The luminescence lifetime of quantum dot quantum well was longer than that of the core-shell structure.