Ultrafast Spectroscopy and Technological Application of Light Harvesting Nanomaterials

In this article, we will review our investigation on the key ultrafast processes in the light harvesting dynamics of Zinc Oxide (ZnO)-based nanomaterials. Firstly, we describe our studies on light harvesting of the complex of ZnO nanoparticles (NPs) with biological probe Oxazine 1 in the near–infrared region using time picosecond-resolved fluorescence decay studies. We have used ZnO NPs and Oxazine 1 as model donor and acceptor respectively to explore the efficacy of the Förster resonance energy transfer (FRET) in the nanoparticle-dye system. It has been shown that FRET from the states localized near the surface and those in the bulk of the ZnO NPs can be resolved by measuring the resonance efficiency for various wavelengths of the emission spectrum. It has been observed that the states located near the surface for the NPs (contributing to visible emission at   550 nm) can contribute to very high efficiency (>90%) FRET. The efficiency of light harvesting dynamics of the ZnO nanorods (NRs) has also been explored in this study and they were found to have much less efficiency (~40%) for energy transfer compared to the NPs. The possibility of electron transfer reaction has ruled out from the picosecond-resolved fluorescence decay of the acceptor dye at the ZnO surface. Secondly, we report the dynamics of light harvesting of ZnO NPs to a surface adsorbed sensitizing dye (SD) N719 (Di– tetrabutylammonium cis–bis(isothiocyanato)bis(2,2’–bipyridyl–4,4’– dicarboxylato)ruthenium(II)). By using picoseconds–resolved FRET technique we have explored that the excited ZnO NPs resonantly transfer visible optical radiation to the SD N719. The consequence of the energy transfer on the performance of the overall efficiency of a model ZnO NP–