Influence Of Metal Nanoparticles On The Fluorescence Of Porphyrins

The highly concentrated incident field by the excited local plasmon resonances of metal nanoparticles have been well known to enhance the luminescence of molecules placed in the near field.However,when the distance between metal nanoparticles and optical molecules is small enough,damped molecular dipole oscillations or orbital hybridization by interface interaction will lead to the fluorescence quenching.The competition of the amplification and inhibition of the fluorophores emission in the near field of metallic NPs can be controlled by tuning the characteristics of NPs and molecule-NPs distances.The correlative research is of great importance to tune molecular fluorescence yield and spectral bands at nanometer scale,and benefit to understand the fundamental physics relating to localized surface plasmons,such as quantum interaction and energy transfer mechanism.In this work,plasmon-enhancement dominance over nonradiative decay at short distances(1 nm – 5 nm)has been observed for submonolayer TPP molecules in the vicinity of the silver NPs,when the resonant absorption and excitation are enhanced in the local near field.The main contents of this thesis can be summarized as follows:1.Seed-mediated growth and layer-by-layer(LBL)method are used to fabricate silverpolymer core-shell nanoparticles(NPs).The size,shape and shell thickness are well controlled to get the plasmonic resonance peak at about 410 nm,which matches very closely with the 405-nm excitation laser.2.Submonolayer porphyrin molecules are prepared by thermal evaporation,verified by scanning tunneling microscope(STM)images.The separation distance for molecules and silver NPs are determined by the thickness of polymer shell,about 1 nm – 5 nm.3.Combined with the calculation results of finite-difference time-domain(FDTD)method,the photoluminescence(PL)spectra and fluorescent lifetimes of submonolayer TPP molecules in the vicinity of the silver NPs demonstrate the plasmon-enhancement dominance over nonradiative decay at short distances(1 nm – 5 nm),when the resonant absorption and excitation are enhanced in the local near field.