Two-dimensional electronic spectroscopy of CdSe nanoparticles at very low pulse power.

摘要: Nanoparticles have been proposed as a promising material for creating devices that harvest, transport, and manipulate energy electrons. Ultrafast charge carrier dynamics represent critical design aspect are dependent on both size shape of the nanoparticle. Spectroscopic investigation electronic structure these systems is complicated by sample inhomogeneity, which broadens peaks leads to ambiguity in interpretation spectra dynamics. Here, we use two-dimensional spectroscopy remove inhomogeneous broadening clarify measured We specifically investigate effect nanoparticle ultrafast band-edge exciton states CdSe quantum dots, nanorods, nanoplatelets. Particle was chosen enable straightforward comparisons effects particle without retuning laser source. The were with low pulse powers (generally <1 nJ/pulse), using short pulses (∼12 fs) minimize interference from solvent contributions spectra, ambiguities due pulse-overlap effects, multi-exciton effects. lowest two clearly resolved dots but unresolved nanorods nanoplates, agreement previous spectroscopic theoretical results. In all nanoparticles, measurements show strong evidence relaxation into state within ∼30 fs, timescale not observable similar systems. These unambiguously assigned hole relaxation, higher lying excited energetically accessible experiments. Clear coherent superpositions seen any particles studied, contrast recent results work dots.