Bright Gradient-Alloyed CdSexS1-x Quantum Dots Exhibiting Cyan-Blue Emission

Highly emissive alloyed CdSeS quantum dots (QDs) with a gradient structure exhibiting photoluminescence (PL) peaking at 490 nm and an absolute quantum yield (QY) of 79% (in toluene with excitation wavelength of 430 nm) were designed and synthesized. The cyan-blue emitters were synthesized at 180 °C in 1-octadecene (ODE) with cadmium oleate (Cd(OA)2), tri-n-octylphosphine selenide (TOPSe), and tri-n-octylphosphine sulfide (TOPS) as the Cd, Se, and S precursors, respectively; importantly, a commercial secondary phosphine, diphenyl phosphine (DPP or HPPh2), was used as a beneficial additive. Also, our high Cd/(Se + S) feed molar ratio aids in shifting the equilibrium of the chalcogenide exchange, TOPE + HPPh2 ⇔ TOP + E═PPh2H, to the right. Density functional theory (DFT) calculations suggest that the formation of Se═PPh2H proceeds faster than that of S═PPh2H, which supports our high S/Se feed molar ratio used to synthesize the bright gradient-alloyed CdSeS QDs. Compositional and structural characterization w...