Exciton Dynamics in Strain-Graded CdSe/ZnSe Core/Shell Quantum Dots

Colloidal semiconductor heterostructures are nanoscale solid state platforms in which it is possible to control charge carrier dynamics through different structural parameters, such as size and geometry. Their unique properties such as high emission quantum yield, polarized absorption and emission, high photostability, and tunable narrow-band emission spectra make these structures promising for efficient optoelectronic applications. In particular, quantum dots with compositionally abrupt interface, which generates a strain-graded core-shell structure, such as the CdSe/ZnSe ones, allow to efficiently tailor the exciton fine structure with suppression of exciton-phonon interactions, which implies multi-peak emission, reduced nonradiative Auger processes and potential longer dephasing processes. In this work, we investigate exciton dynamics in wurtzite CdSe/ZnSe strain-graded quantum dots (sg-QDs). The influence of strain on the intraband dynamics and exciton and multi-exciton interactions in these structures are studied through transient photoluminescence and transient absorption techniques. We demonstrate that sg-QDs exhibit reduced Auger recombination rates and reduced influence from delayed emission, which accounts for less than 0.01% of the total emission, different from the observed in regular type-I and quasi-type-II heterostructures, turning them interesting platform for application in light emitting devices.