Plasmonic Modulation On Photon Emission Behavior Of Semiconductor Quantum Dot

Nanophotonics has been an active and evolving in the past two decades that aims at creating nanoscale field for optics and understanding their optical properties.The fabrication and application of nanophotonic devices are widely studied across various disciplines.Nanophotonic elements are capable of concentrating light beyond the classical diffraction limit and manipulating light-matter interaction at the nanoscale.Plasmonic nanostructures can manipulate light at the sub wavelength scale beyond the optical diffraction limit,which is considered a powerful platform for achieving optoelectronic integration and all optical integration in the micro/nano scale.However,how to effectively regulate the emission behavior of photons using plasmonic nanostructures at the nanoscale is an urgent scientific problem to be solved.Quantum dots（QDs）have been widely used in optoelectronic devices and bioimaging for their unique optical characteristics,such as high color purity,high absorption cross-sections,photostability and high photoluminescence quantum efficiency.Plasmonic metal nanoparticles and QDs are two important nanophotonic elements.The exciton-plasmon interaction in the metal-semiconductor nanostructures can alter the exciton generation and recombination dynamics of the QDs.The extraordinary optical properties of surface plasmons in metal nanostructures provide the possibilities to manipulate the radiative and non radiative rates of exciton decay,and modify the emission photon statistics.Although there have been many studies on the plasmonic effect on the emitting properties of QDs,it still remains challenging to provide further insights into the fundamental mechanism of the exciton-plasmon interaction.To overcome these challenges,single particle studies are necessary.In this study,we have chosen gold（Au）nanoparticles to provide a local plasmon field,and Cd Zn Se S/Zn S QDs are selected as exciton sources.The polymethyl methacrylate（PMMA）and Si O₂ are used as dielectric material to construct nanocomposite layers Au/PMMA/QDs and hybrid Au@Si O₂-QDs systems,respectively.These two nanostructures have been studied to investigate the plasmonic modification on the optical and photophysical properties of QDs by employing single molecule fluorescence lifetime imaging microscopy（FLIM）and second-order photon intensity correlation（g²（τ））measurements.The main studies are as follows:We have constructed and adjusted a single molecule dynamics measurement system to make it more comprehensive and optimized.This article provides a detailed introduction to the design concept of single molecule dynamics measurement system and Hanbury Brown and Twiss（HBT）setup,the selection of experimental instruments,and the optimization of the entire system.The nanocomposite layers Au/PMMA/QDs have been firstly studied by employing single molecule fluorescence lifetime imaging microscopy（FLIM）and second-order photon intensity correlation（g²（τ））measurements.In the presence of localized surface plasmon of Au nanoparticle,the QDs demonstrate a significant enhancement in photoluminescence（PL）intensity,suppressed blinking,reduced lifetime and enhancement of multiphoton emission.The hybrid Au@Si O₂-QDs nanostructures with regulated spacer thickness have been studied.The distance between the Au nanoparticle and QDs was optimized to～8 nm to realize the maximum fluorescence enhancement.The hybrid nanostructures Au@Si O₂-QDs demonstrate a significant enhancement in PL intensity,non-blinking,and multiphoton behavior.Compared with Au/PMMA/QDs,the preparation of nanocomposite structures is more controllable,and the PL intensity,lifetime,g²（0）are more concentrative in distribution.