Photoluminescence depending on the ZnS shell thickness of CdS/ZnS core-shell semiconductor nanoparticles

A core/shell type semiconductor nanoparticle of CdS/ZnS emits visible light under ultra-violet illumination, whose emission wavelength depends on the particle diameter and ZnS shell thickness. This paper describes the dependence of the shell thickness on the amount of added ZnS precursor in the synthesis process and its impact on photoluminescence. The synthesis is done by the microemulsion method in AOT surfactant reverse micelles containing water. The precursor amount is varied by two different ways (1) increasing water content, at a given precursor concentration or (2) increasing the precursor concentration at given water content. It is found that the nanoparticle diameter and the shell thickness almost linearly increase when the water content trapped in the reverse micelles increases. Similarly, the diameter increases with the precursor concentration inside the micelles. The nanoparticle size also increases with the time of aging in an inert gas because of the increase of the ZnS shell thickness.