Alloyed quantum dots (QDs) passivated with shell materials have valuable optical characteristics suitable
for a wide array of applications. In this work, alloyed ternary CdSeS QDs passivated with ZnSeTe and
ZnSeTe/ZnS shells have been synthesized via a hot-injection method and a ligand exchange reaction
employing L-cysteine as a thiol ligand has been used to obtain these water-soluble nanocrystals for the
first time. The photoluminescence (PL) quantum yield (QY) of alloyed L-cysteine-capped CdSeS was
71.2% but decreased significantly to 5.2% upon passivation with a ZnSeTe shell. The red shift in PL emission
of the CdSeS/ZnSeTe QDs was attributed to be strain-induced whilst a lattice-induced process likely
created defect states in the core/shell interface hence contributing to the decline in the PL QY.
Nonetheless, the fluorescence stability of CdSeS/ZnSeTe QDs in aqueous solution was unperturbed.
Further passivation with a ZnS shell (CdSeS/ZnSeTe/ZnS) improved the PL QY to a value of 58.7% and thus
indicates that the defect state in the QDs core/shell/shell structure was reduced. PL lifetime exciton measurements
indicated that the rates of decay of the QDs influenced their photophysical properties