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Chemical Structure, Ensemble and Single-Particle Spectroscopy of Thick-Shell InP–ZnSe Quantum Dots

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journal contribution
posted on 2017-12-28, 00:00 authored by Kemar R. Reid, James R. McBride, Nathaniel J. Freymeyer, Lucas B. Thal, Sandra J. Rosenthal
Thick-shell (>5 nm) InP–ZnSe colloidal quantum dots (QDs) grown by a continuous-injection shell growth process are reported. The growth of a thick crystalline shell is attributed to the high temperature of the growth process and the relatively low lattice mismatch between the InP core and ZnSe shell. In addition to a narrow ensemble photoluminescence (PL) line-width (∼40 nm), ensemble and single-particle emission dynamics measurements indicate that blinking and Auger recombination are reduced in these heterostructures. More specifically, high single-dot ON-times (>95%) were obtained for the core–shell QDs, and measured ensemble biexciton lifetimes, τ2x ∼ 540 ps, represent a 7-fold increase compared to InP–ZnS QDs. Further, high-resolution energy dispersive X-ray (EDX) chemical maps directly show for the first time significant incorporation of indium into the shell of the InP–ZnSe QDs. Examination of the atomic structure of the thick-shell QDs by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) reveals structural defects in subpopulations of particles that may mitigate PL efficiencies (∼40% in ensemble), providing insight toward further synthetic refinement. These InP–ZnSe heterostructures represent progress toward fully cadmium-free QDs with superior photophysical properties important in biological labeling and other emission-based technologies.