Comparison of the properties of composition-tunable CdSe–ZnSe and Zn xCd 1− xSe nanocrystallites: Single- and double-pot synthesis approach

Abstract

In this work, a simple, effective and reproducible synthetic route (single-pot (SP) approach) for the preparation of high quality core–shell CdSe–ZnSe quantum dots without the use of any pyrophoric organometallic precursors is presented and their properties are compared with those prepared by the conventional double-pot (DP) approach. Effective surface passivation of stoichiometric, monodispersed, small-sized (∼5 nm) CdSe nanocrystallites is achieved by coating them with a ZnSe shell by single-pot approach. The resulting core–shell nanocrystallites exhibit high quantum yield values ∼11.33%, narrow line-width of the PL band, stable surface-bonds configuration and superior structural properties at lower Zn content (∼10 at.%). With increasing Zn content (≥20 at.%), a composition-tunable emission across the visible spectrum has been demonstrated by a systematic blue-shift in emission wavelength due to the formation of ternary Zn x Cd 1− x Se quantum dots with acceptable luminescence properties. Here, contribution to emission process from surface states of nanocrystallites increases with zinc content. The core–shell and ternary QD's formed by different routes are modeled, based on the observations of several complimentary techniques (XPS depth-profiling, PL, UV–VIS absorbance, TEM/SAED). The improved properties of core–shell CdSe–ZnSe quantum dots with similar zinc content using single-pot synthesis approach as compared to the corresponding samples obtained by double-pot synthesis, is due to better-passivation effect rendered by thin ZnSe-shell in the SP approach. Their strong luminescence, narrow emission bands and wide colour-tunability makes such quantum dot structures attractive for various scientific and commercial applications.