Gram-scale one-pot synthesis of highly luminescent blue emitting Cd _1-xZn_xS/ZnS nanocrystals

We demonstrated a facile synthesis of highly luminescent blue emitting Cd_1-xZn_xS/ZnS core/shell structured nanocrystals (NCs) in straightforward and reproducible manner. The alloyed Cd_1-xZn _xS cores with homogeneity in both size and composition were prepared by introducing S precursors (S dissolved in the noncoordinating solvent (1-octadecene)) into the mixed solution of Cd-Oleate (Cd(OA)₂) and Zn-Oleate (Zn(OA)₂) at elevated temperature (300 °C). ZnS shells were successively overcoated on the prepared cores by the second injection of S precursors (S powder dissolved in tributylphosphine, TBPS) directly into the reactor with existing alloyed Cd_1-xZn_xS NC cores without any purification steps. The prepared NCs exhibit strong band edge emission with high photoluminescent quantum yield (PL QY, up to 80%) and narrow spectral bandwidth (fwhm < 25 nm), which is believed to originate from the successful growth of ZnS shell layers on the Cd_1-xZn_xS cores and the interfacial compatibility between Cd_1-xZn_xS cores and the ZnS shell layers through the intradiffusion of Zn atoms from the ZnS shells into the Cd_1-xZn_xS cores during the shell formation reaction. The emission wavelength (PL λ_max.) of Cd_1-xZn _xS/ZnS core/shell NCs was finely tuned from violet (415 nm) to blue (461 nm) by adjusting the amount of S precursors in the first injection (S in 1-octadecene) and thus changing actual Cd content ratio in the alloyed Cd _1-xZn_xS cores (0.49 ≤ x ≤ 0.76). Furthermore, multigram (3 g) scale production of Cd_1-xZn_xS/ZnS core/shell NCs with narrow size distribution and spectral bandwidth was also demonstrated.