Charge separation in colloidal semiconductor nanocrystals (CSNCs) is one of the key processes for the development of highly efficient solar cells. Several types of CSNCs have been recently synthesized with controlled quantum confinement dimensionality such as quantum dots (QDs), nanorods (NRs), and nanoplatelets (NPLs). However, previous studies on the carrier extraction dynamics from CSNCs have focused on QDs and NRs. Here, we analyzed the electron transfer process from colloidal CdSe NPLs to methyl viologen (MV 2+ , electron acceptor) using luminescence decay measurements and femtosecond pump−probe spectroscopy. We examined the dependence of the electron transfer dynamics on the lateral size of CdSe NPLs and found that the rate of electron transfer from CdSe NPLs to MV 2+ depends on the NPL face where MV 2+ adsorbs. In addition, we analyzed the growth kinetics and initial bleach amplitude at the band-edge bleach of CdSe NPLs and CdSe NPL−MV 2+ complexes and found that, in contrast with the behavior of CdSe QD−MV 2+ and NR−MV 2+ complexes, hot electron transfer does not occur. This result is a consequence of fast intraband relaxation in CdSe NPLs and the relatively slow electron transfer process.

Recently, much attention has been paid to semiconductor–metal hybrid nanostructures (HNs) in terms of efficient electron transfer from the semiconductor to the metal and semiconductor–metal HNs are one of the best candidate materials for photovoltaics and photocatalysis. However, the analyses of electron-transfer processes in semiconductor–metal HNs have focused on the electron transfer from the band-edge state in metal-attached semiconductor nanorods. Here, we synthesized and characterized CdSe quantum dots (QDs) attached with different-sized Au nanoparticles (NPs) and examined electron transfer from band-edge (1S­(e)) and higher excited states using femtosecond pump-probe spectroscopy with state-selective excitation. We analyzed growth kinetics, decay dynamics, and initial bleach amplitude of the 1S bleach band and found the existence of hot electron transfer from the 1P­(e) state and ultrafast electron transfer with the lifetime much shorter than the instrumental response function (≪60 fs) from the 1S­(e) state of CdSe QDs to Au NPs. The lower 1S bleach yields of CdSe QD–Au HNs excited at 400 nm and 1P states as compared with those of CdSe QDs can be explained in terms of hot electron transfer from the 1P­(e) state and ultrafast electron transfer from the 1S­(e) state.

The bandedge PL peak wavelength of ZnTe–AgInTe2 solid solution nanocrystals was tunable in the near-IR region by changing their chemical composition.

The development in optical trapping and manipulation has been showing rapid progress, most of it is in the small particle sizes in nanometer scales, substituting the conventional continuous-wave lasers with high-repetition-rate ultrashort laser pulse train and nonlinear optical effects. Here, we evaluate two-photon absorption in optical trapping of 2.7 nm-sized CdTe quantum dots (QDs) with high-repetition-rate femtosecond pulse train by probing laser intensity dependence of both Rayleigh scattering image and the two-photon-induced luminescence spectrum of the optically trapped QDs. The Rayleigh scattering imaging indicates that the two-photon absorption (TPA) process enhances trapping ability of the QDs. Similarly, a nonlinear increase of the two-photon-induced luminescence with the incident laser intensity fairly indicates the existence of the TPA process.