Separating fluorescent species of aqueous PbS semiconductor nanocrystals usingmicro-emulsions

Abstract

Colloidal PbS nanocrystals over-coated with CdS are prepared in aqueous solutions andexhibit strong photoluminescence with two distinct peaks in the visible regime. Aphotoluminescence peak is observed at 640 nm, which is attributed to the band edgerecombination in the PbS nanocrystals, and another peak at 510 nm, which is above theband edge of the PbS nanocrystals. The two PL peaks are isolated by extracting separatespecies of nanocrystal based upon their surface morphology. Micro-emulsions ofhexane:PVA are used to remove the species containing the PL peak at 640 nm from thesolution, leaving a singular peak at 510 nm. We show conclusively that the double-peakedstructure observed in the photoluminescence spectra of PbS nanocrystals over-coatedwith CdS is due to the presence of two distinctly different nanocrystal species.