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

摘要

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 bi-exciton 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 shows 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 sub-populations of particles that may mitigate PL efficiencies (~ 40% in ensemble), providing insight towards further synthetic refinement. These InP-ZnSe heterostructures represent progress toward fully cadmium-free QDs with superior photo-physical properties important in biological labeling and other emission-based technologies.