State-to-state exciton dynamics in semiconductor quantum dots

Using two-dimensional photon echo spectroscopy to probe the fine structure of the ground state biexciton of CdSe nanocrystals

“…Klimov et al [43] have assigned this negative feature to be due to excited state absorption, which agrees with our analysis. This negative feature was examined in greater detail by Sewall et al [14][15][16] who found that the size of this feature depended on a number of factors, such as a biexcitonic state probed (1S or 1P), and the size of the NC. Further experiments are currently being conducted in our group to investigate these effects using the 2DPE technique.…”

“…Most efforts thus far have utilized transient absorption to determine biexcitonic binding energies, the biexcitonic Stokes shift, the size dependence of these properties, and lifetimes of the biexciton [1,4,[14][15][16]. Sewall et al [14] have found that both the apparent biexciton binding energy and the biexciton Stokes shift are larger than the corresponding values for the single ground state exciton.…”

“…This involves excitation into high energy bands of the NC and the production of multiple excitons at lower energy levels. As a result, many recent studies have examined higher multiexcitonic states, their lifetimes, and relaxation mechanisms to lower lying excitonic states [1,4,[14][15][16][17]. However, despite the great interest in this phenomena, very little is known about the electronic structure of these excitons, in particular the fine structure, since the inhomogeneous broadening of samples and the density of states [18] has proven to be prohibitive to experimental study of these states.…”

Two‐Dimensional Visible Spectroscopy For Studying Colloidal Semiconductor Nanocrystals

“…The decay of a bleach feature accompanied by the increase of a lower energy bleach feature with the same characteristic time constant is a clear signature of exciton relaxation. [44][45][46] However, if the two transitions are already coupled, i.e., they already share a common state, then pumping one of these transitions will instantaneously bleach the other. In this case, no change will be observable over time unless the multiplicity of the common electronic state is larger than the one of the other charge carrier states.…”

Förster Resonance Energy Transfer Mediated Photoluminescence Quenching in Stoichiometrically Assembled CdSe/ZnS Quantum Dot-Peptide Labeled Black Hole Quencher Conjugates for Matrix Metalloproteinase-2 Sensing

“…[40][41][42] This heterogeneity leads to a variety of decay processes available to band-edge excitons, where each observed time constant, τ, is an average excited state lifetime for a population of QDs with a set of available decay pathways ranging in time scale from hundreds of femptosecond to microseconds. [43][44][45][46][47][48][49] In addition to radiative recombination, decay of the excited state population depends on several competing radiationless processes such as Auger relaxation of hot electrons, 47,50 spin relaxation, [51][52][53] phonon induced carrier relaxation, 54 biexciton decay, 55 carrier traping 56,57 at nanocrystal defects, charge transfer into ligand based orbital and relaxation to the ground state. For the convenience of researchers, second or third-order non-linear fitting is applied from time to time to in order to fit the decay profile.…”