Ultrafast and Hot Electron Transfer in CdSe QD–Au Hybrid Nanostructures

Abstract

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.

Hot electron transfer in Zn–Ag–In–Te nanocrystal–methyl viologen complexes enhanced with higher-energy photon excitation

“…This indicated that the number of photogenerated electrons that relaxed to the conduction band-edge state became smaller for ZAITe-MV 2+ complexes, owing to the extraction of hot electrons with MV 2+ . The value of f HET can also be estimated by the following equation: 17 f HET (%) ¼ {1 À (DOD ZAITe-MV 2+/DOD ZAITe )} Â 100.…”

“…Furthermore, it should be noted that the f HET of 72%, observed for ZAITe NC-MV 2+ complexes, was comparable to those reported for CdSe naonrod-MV 2+ complexes, >50%, 7 and for CdSe-Au hybrid NPs, 48%. 17 This suggests that ZAITe NCs are a promising material to utilize the excess energy of incident photons for improving the conversion efficiency of quantum dot solar cells.…”

“…Charge separation dynamics with the use of various electron acceptors has been reported in many papers. [5][6][7][8][9][10][11][12][13][14][15][16][17] For example Banin et al reported that hybrid nanostructures of Au-tipped CdS nanorods with a larger Au size exhibited a higher probability for charge separation of multiple excitons formed in the CdS nanocrystals, improving the photocatalytic activity for H 2 generation. 15 The rate of photoinduced electron transfer from CdSe NCs to methyl viologen (MV 2+ ) was shown to be dependent on the particle morphology: plate-like CdSe NCs exhibited a slower rate than that of spherical or rod-shaped CdSe NCs due to the weak electronic coupling along the short and long axes in the lateral dimension.…”

Ultrafast Electron Transfer in Binary Nanoparticle Superlattices under High Pressure

“…In addition, the smaller Au NCs had a smaller state density; thus, small-sized Au NCs did not have obvious spectral features. [20] Therefore, CdSe/ZnS QDs played a dominant role in determining the spectra of BNSLs. Moreover, absorption and PL peaks of BNSLs have a little difference to isolate CdSe/ZnS QDs.…”

“…According to previous reports, the decreased size of the Au NCs can increase the ET time in the heterostructure. [20] However, the size of the particle and interparticle spacing affects the ET process of BNSLs under pressure. The reduced interparticle spacing can increase the electron interaction and facilitate ET between CdSe/ZnS QDs and Au NCs.…”