Using Shape to Control Photoluminescence from CdSe/CdS Core/Shell Nanorods

CdSe/CdS core/shell nanorods can exhibit high photoluminescence quantum yields, but it is not yet clear what processes determine the yields and how they can be controlled. Moreover, the effective band alignment between the core and the shell affects quantum yield, but its nature is still under debate. We systematically studied quantum yields when the shell is excited as a function of both core size and shell volume. Using time-resolved photoluminescence decay measurements and transient-absorption spectroscopy, we found that quantum yields are determined by a balance between radiative and nonradiative recombination rates, and not by single-carrier trapping. The radiative recombination rate decreases as the nanorod volume increases, independent of the core size. The results indicate that high quantum yields can be obtained only by limiting the size of the shell and point to an effective quasi-type-II band alignment for all of the nanorods in this study.