Organometallic synthesis, structural and optical properties of CdSe quantum dots passivated with ternary AgZnS alloyed shell

Abstract

We report on the surface passivation of a new alloyed ternary AgZnS shell layer on luminescent CdSe quantum dots (QDs) via the organometallic hot-injection pyrolysis of metal precursors, surfactant precursors and organic ligands in a non-coordinating solvent. Transmission electron microscopy, X-ray diffraction, Raman spectroscopy and UV/vis absorption and fluorescence emission spectrophotometry were used to characterize the QD nanocrystals. Fixed AgZnS shell alloying was used as the main fabrication strategy to engineer the band gap of CdSe/AgZnS core/alloyed shell QDs which in turn led to a blended mixture of homogenous and heterogenous particle size growth with spherical, quasi-spherical and trigonal-shaped particles. The crystal structure of CdSe/AgZnS QDs was mainly zinc blende but as the QDs size increased with time, a superimposition of zinc blende and wurtzite hexagonal structure was observed with the former being predominant in the diffraction pattern. The photoluminescence (PL) emission spectra of CdSe/AgZnS QDs were tuned across the visible region while the full width at half maximum was as low as 33 nm, representing an 8 nm decrease compared to 41 nm FWHM exhibited by CdSe QDs. As CdSe/AgZnS core/alloyed shell QDs grew with time, the PL quantum yield (QY) increased from 67% for CdSe to a maximum of ~100% for CdSe/AgZnS QDs and thereafter decreased steadily to a minimum of 36% upon further growth. By achieving ~100% PL QY, it appears that interfacial surface defect states in the core/alloyed shell QDs were completely eliminated via the AgZnS shell alloying process on the CdSe core. The unique optical properties exhibited by CdSe/AgZnS core/alloyed shell QDs as reported in this work shows great promise for light emitting QD applications.