Carrier relaxation pathway of semiconductor nanomaterial and semiconductor-metal hybrid nanomaterial

Abstract

The carrier dynamics in semiconductor nanomaterials, CdSe nanorods of different length, was systematically studied. As a result, the understanding of the exciton relaxation pathway was extended to unveiling the CdSe nanorods electron-transfer mechanism in semiconductor-metal hybrid nanomaterial. We explored photo-generated exciton dynamics of the CdSe nanorods using time-resolved absorption and photoluminescence (PL) spectroscopy spanning sub-ps to μs time domain. We controlled the fluence and wavelength of photoexcitation and the length of nanorods. The combined time-resolved spectroscopic study revealed the fast Auger recombination [1] and the shallow-trap [2] and band-edge relaxations in the bare-rod system. For the semiconductor-metal hybrid systems, the majority of bleach recovery was found to follow ultrafast (<300 fs) channels. Additionally, minor slow bleach components were also observed in μs time scale. With the correlated time-resolved electronic spectroscopic methods covering a wide time window and broadband sensitive to dark and luminescent states, we complete the carrier-relaxation mechanism of the CdSe nanorod and the CdSe-metal hybrid systems. From the comparison of the photocatalytic activities [3] of the semiconductor-metal hybrid nanostructures, it is revealed that the minor electron-transfer channels via metal trap sites (10`s of μs relaxation components) are key to the photocatalytic activities.