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Giant-shell CdSe/CdS core/shell nanocrystals have attracted much attention due to their unique quasi-type-II band alignment, where a large valence band offset confines holes strongly to the core but electrons are delocalized due to a small conduction band offset. Here, we report the observation of the relative enhancement in the radiative recombination rate of a biexciton compared to that of an exciton in giant-shell CdSe/CdS nanocrystals. We found a clear correlation between the shell thickness of the CdSe/CdS nanocrystals and the ratio between the radiative recombination rates of the biexciton and exciton. Our finding can be explained by a picture in which the biexciton emission efficiency is enhanced through electron localization around the core due to the strong Coulomb potential of the two holes confined in the core.

Metal–halide perovskite nanocrystals (NCs) are promising photonic materials for use in solar cells, light-emitting diodes, and lasers. The optoelectronic properties of these devices are determined by the excitons and exciton complexes confined in their NCs. In this study, we determined the relaxation dynamics of charged excitons and biexcitons in CsPbBr3 NCs using femtosecond transient-absorption (TA), time-resolved photoluminescence (PL), and single-dot second-order photon correlation spectroscopy. Decay times of ∼40 and ∼200 ps were obtained from the TA and PL decay curves for biexcitons and charged excitons, respectively, in NCs with an average edge length of 7.7 nm. The existence of charged excitons even under weak photoexcitation was confirmed by the second-order photon correlation measurements. We found that charged excitons play a dominant role in luminescence processes of CsPbBr3 NCs. Combining different spectroscopic techniques enabled us to clarify the dynamical behaviors of excitons, charged ex...

The temporal fluctuations in the photoluminescence (PL) spectra of single CdSe/ZnS nanocrystals (NCs) exhibiting PL blinking at room temperature as well as their dynamical properties were studied. In the case of large NCs, measuring the time-dependent PL intensities and lifetimes allowed us to separately characterize the degree of spectral diffusion (SD) of the exciton and trion (charged exciton) emissions. The SD properties, such as the polarizability and field fluctuation, were investigated quantitatively through comparisons with the results of numerical calculations based on a simple field fluctuation model. We found that trion emissions exhibit unique SD characteristics; i.e., their binding energies are positive and their polarizabilities are smaller than those of excitons. In addition, we observed that the exciton emissions exhibited size-dependent SD behaviors, reflecting the differences in the polarizabilities of the NCs with different sizes. Finally, the experimental data, including an analysis of...