Optical Properties and Exciton Dynamics of Alloyed Core/Shell/Shell Cd1-xZnxSe/ZnSe/ZnS Quantum Dots

In this study we introduce a new method for the onepot synthesis of core/shell/shell alloyed Cd1-xZnxSe/ZnSe/ZnS QDs and examine the effect of the shell coating on the optical properties and exciton dynamics of the alloy core. The photoluminescence (PL) quantum yield is greatly enhanced after shell growth, from 9.6% to 63%. The exciton dynamics were studied by time correlated single photon counting (TCSPC) and fit using integrated singular value decomposition global fitting (i-SVD-GF), which showed the biexponential observed lifetimes on the nanosecond time scale remain the same after shell growth. Using ultrafast transient absorption (TA) spectroscopy and SVD-GF, we have determined that surface passivation by ZnSe and ZnSe/ZnS shells reduces nonradiative recombination primarily on the picosecond time scale. These findings are helpful in directing the development of the next generation of QDs for biological labeling and other applications.