| Abstract | Highly emissive ultraviolet ZnSeS nanocrystals (NCs), with a core–shell-like structure, were designed and synthesized via a one-step noninjection approach in 1-octadecene (ODE). These ultraviolet ZnSeS NCs exhibit bright bandgap emission with high color purity and little trap emission. With full width at half-maximum (fwhm) of 21 nm only, photoluminescent (PL) quantum yield (QY) of 60% was estimated for one ensemble dispersed in toluene exhibiting bandgap absorption peaking at 380 nm and bandgap emission at 389 nm. These alloyed ZnSeS NCs present a cubic crystal structure consisting of a Se-rich core and a S-rich shell. Such a gradiently alloyed structure was suggested by our investigation on the temporal evolution of optical properties of the growing ZnSeS NCs monitored from 80 to 300 °C, together with structural and compositional characterization performed with XRD, XPS, EDX, and TEM. This newly developed one-step noninjection approach was achieved with zinc oleate (Zn(OA)2), diphenylphosphine selenide (SeDPP), and diphenylphosphine sulfide (SDPP) as Zn, Se, and S precursors, respectively. ZnSe monomers mainly participated in nucleation at 120 °C, while both ZnSe and ZnS monomers contributed to NC formation in later growth stages (160 °C and higher). 31P NMR study demonstrates that SeDPP is more reactive than SDPP toward Zn(OA)2, and also supports such a model proposed on the combination of ZnSe and ZnS monomers leading to nucleation/growth of ZnSeS alloyed NCs. The present study offers conceptual methodology to various highly photoluminescent alloyed NCs with high quality, high particle yield, and high synthetic reproducibility. |
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