Synthesis and properties of PbSexS1-x alloyed nanocrystals

We present a comparative study of colloidal PbSexS1-x alloyed nanocrystals (NCs) with variation of chemical composition and different structure (core-shell and homogeneous) prepared by a single-injection procedure with respect to corresponding PbSe core NCs and PbSe/PbS core-shell NCs prepared by the traditional two-injection procedure. The narrow band edge of absorption and photoluminescence 1S-exciton energy of PbSexS1-x alloyed NCs were tuned (blue shifted) from the band edge of the same size PbSe NCs to the band edge of PbS NCs by controlling the Se+S/Pb molar ratio in the synthetic mixture. The magnitude of the Stokes shift was found to be dependent upon the size of NCs and on the core(shell) chemical composition. The largest Stokes shift (100 meV) was observed in the smaller PbSe NCs, while PbSexS1-x core-alloyed shell NCs prepared by a single-injection procedure show the vanishing small Stokes shift.