Static and Dynamic Emission Quenching in Core/Shell Nanorod Quantum Dots with Hole Acceptors

CdSe/CdS and CdSe/ZnS core/shell nanorods have been synthesized with various shell thicknesses and characterized by TEM. The CdSe cores have in aspect ratio of 5.0 +/- 0.7. The TEM results show that there are different axial and radial shell growth rates. Shell deposition maintains the rod morphology, with a final aspect ratio of 4.1. The presence of the US or ZnS shell greatly affects the particle nonradiative relaxation dynamics and hence the luminescence quantum yields. Both types of shells passivate the surface, reducing the extent of both static and dynamic quenching. Two types of hole acceptors, phenothiazine and hexadecane thiol, have been adsorbed onto these core/shell nanorods, and the effects on the luminescence dynamics are studied using static and time-resolved spectroscopy. ZnS- and CdS-coated particles with adsorbed hole acceptors show differing extents of static and dynamic quenching. These differences may be understood in terms of the different shell morphologies, valence band offsets, and the differences in the phenothiazine and thiol energetics. The extents of static and dynamic quenching are also studied as a function of the phenothiazine or thiol concentration. In both the ZnS- and CdS-coated particles, these concentration dependencies indicate that static quenching is associated with strongly binding sites, presumably where the quencher is bound at a defect in the shell. Dynamic quenching is associated with more weakly binding sites on the surface of the particle.