Deposition of CdS, CdS/ZnSe and CdS/ZnSe/ZnS shells around CdSeTe alloyed core quantum dots : effects on optical properties

摘要

In this work, we have synthesized water-soluble L-cysteine-capped alloyed CdSeTecore QDs and investigated the structural and optical properties of deposition of eachof CdS, CdS/ZnSe and CdS/ZnSe/ZnS shell layers. Photophysical results showedthat the overcoating of a CdS shell around the alloyed CdSeTe core (QY = 8.4%)resulted in an effective confinement of the radiative exciton with an improved QYvalue of 93.5%. Subsequent deposition of a ZnSe shell around the CdSeTe/CdSsurface decreased the QY to 24.7% but an increase in the QY value of up to 49.5%was observed when a ZnS shell was overcoated around the CdSeTe/CdS/ZnSesurface. QDs with shell layers showed improved stability relative to the core. Dataobtained from time-resolved fluorescence measurements provided useful insightinto the variations in the photophysical properties of the QDs upon the formation ofeach shell layer. Our study suggests that the formation of the CdSeTe/CdScore/shell QDs meets the requirements of quality QDs in terms of high PL QY andstability, hence further deposition of additional shells are not necessary in improvingthe optical properties of the core/shell QDs.