The Optical Properties Of Noble Nanoparticals And The Energy Transfer Between Semiconductor Quantum Dots

Metallic nanoparticles have strong plasmon resonance absorption and the enhancement of the local electromagnetic fields, since the existence of surface plasmons. They can create strong local optical field, which leads to various optical enhancement effects, such as surface-enhanced Raman scattering, enhanced photo luminescence and enhanced optical nonlinearity. Basing on those characteristics, it has a wide range of possible applications in optical storage, nonlinear spectra, biolabels and ultrafast information processes.Semiconductor quantum dots (QDs) have been attracted increasing interest in recent years for their particular optical properties of size-dependent tuning, narrow fluorescence emission bands and high quantum yields, etc. The optical properties of QDs can be operated by controlling the size and structure of QDs. Several important quantum operations, such as Rabi oscillations, control-NOT gate and population swap have been implemented in a single SQD. Very recently, manipulating interactions and coupling between two or more SQDs have been attracted increasing interest, which are critical important for both fundamental research and further practical applications to SQDs-based quantum information processing. Coulomb interaction is a key process for the coupling of optically excited SQDs, which can lead to Forster resonant energy transfer (FRET) between SQDs.In this paper, we synthesized the optical properties of Au-SiO2 crystal column film, and investigated the Forster resonance energy transfer (FRET) between Ag nanoparticls and QDs.(1) The PL of Au-SiO2 crystal columns involved two-and three-photon processes in p-polarized laser, and only two-photon process in s-polarized laser. With an increase of the laser power, the slope (?)log(PL intensity)/(?)log(laser power) changed from 2 to 3, which indicated that the PL of Au-SiO2 crystal columns were induced by two-and three-photon absorption, respectively. We believe that the field enhancement effects play a predominating role in the transformation from two-photon process to three-photon process. (2)Ag nanoparticles (NPs) are prepared by using modified Polyol method. The absorption spectra of the Ag NPs with the diameter (2RAg) in the range 20-170 nm. It indicates that small Ag NPs only have dipole plasmon while large Ag NPs exhibit both dipole and quadrupole plasmon. As 2RAg increases from 20 nm to 110 nm, the dipole plasmon resonances of Ag NPs suspended in water redshifts from 410 nm to about 590 nm. The strong absorption near 430 nm of large Ag NPs (2RAg > 80 nm) is attributed to the quadrupole plasmon resonances.(3) The QDs monolayer films are prepared by using self-assembled technique. Large Ag NPs show strong both quadrupole and dipole plasmon resonance. By using dual-resonance nanoantenna (Ag NPs with diameter 110 nm), the optimized PL ratio of acceptor-to-donor increases to as high as 13.6 and the PL enhancement of acceptor QD reaches 21.2. The large PL enhancement of acceptor is attributed to the collaboration of dipole and quadrupole plasmon of dual-resonance nanoantenna. The Forster transfer efficiency is estimated to be aboutηFRET≈85%.(4) Highly efficient energy transfer of CdSe QDs monolayer enhanced by large Ag/SiO2 core-shell NPs. The PL enhancement factor of acceptor QD-A is-47, PL intensity ratio of acceptor-to-donor reaches-14, energy transfer rate is estimated to" be-0.4 ns-1 and the energy transfer efficiency reaches-86%when the thickness of SiO2 is 7 nm. Our observations demonstrated that the plasmon is an efficient tool to enhance the Coulomb interactions between QDs. We found that the theoretical calculations were in accordance with experimental data.