Localized Surface Plasmon Enhanced Photoluminescence Of Nano Metal And Fluorescent QDs Composite System

The optical properties of noble metal nanoparticles(NPs) and their application in surface enhanced photoluminescence(PL) are hot in the study of nano science.The PL quenching has been often observed in the metal colloid films.To overcome this problem and have stable PL enhancement,the several factors on surface enhanced PL, including the shape and size of Au(Ag) nanoparticles(NPs),the coupling style between the metal NPs and fluorescent quantum dots(QDs) are studied in this thesis. Besides,the mechanism of the PL enhancement is also studied based on the enhanced electric magnetic local field,which is caused by surface plasmon resonance.In the introduction,the characterization,development and the application of the surface plsmon resonance(SPR) enhanced photoluminescence are demonstrated.In chapter 2,firstly,the electron structure and the superior optical properties ofâ…¡-â…¥semiconductor nanocrystals are analyzed.Secondly,the optical properties of moble metal NPs,especially the properties of SPR,are studied deeply.Based on the above research,the condition,influences and mechanism of SPR enhanced PL are discussed thoroughly.The three major works are shown after chapter 3.The first work is the influences of the preparation on the size and optical properties of the bare QDs and core shell QDs.The second work is the influences of Ag colloid films with different shapes on SPR enhaced PL.Finally,the PL enhancement and quenching of nano Au/nano CdSe are studied,the NPs Au are coupling with the NCs CdSe by two modes(layer by layer and NPs dispersal).Factually,the mentioned three works are shown in chapters 3,4,5, respectively.The major works and the innovation in this thesis are shown following:1.The fluorescent QDs CdSe with the size 1～5nm and the emission 500nm～620nm are controlled accurately from the reaction time. Correspondingly,the QDs with emission at various obvious wavelengths can be obtained by preparing CdSe,CdS and CdTe with different sizes.And the research indicates that the final size and concentration of the QDs are decided by the nucleation and growth temperature.Besides,the choice and the ratio of the surfactant influence the potential energy of the growth,that is to say,the speed of the QDs growth can be tuned by the surfactant.The preparation and the optical properties of the core shell CdSe/CdS are major works in this chapter.The emission intensity of CdSe QDs is observed enhanced by 3 times,as the CdSe QDs are coated by CdS shell with different thickness.Meanwhile,the Raman spectroscopy is first proposed to determine the shell thickness according to the research of the change of raman scattering of CdSe/CdS with the shell thickness.2.The morphology of silver colloids evolves from a complex mixture of nanoparticles and nanowires to worm-like nanostructure,and finally to quasi-nanospheres by the annealing of Ag colloid films at different temperatures (200～350℃).The PL enhancements of CdSe QDs dispersed in PMMA on the Ag colloid film with different morphologies,including the as-grown and the annealed Ag colloid films,are the most important research in this chapter,which is also the creative work in this thesis.The PL enhancement factors of CdSe QDs on the as-grown and worm-like Ag colloids film are 2 and 15,respectively.The enhancement factor 15 is first obtained on the metal colloid film,as far as we known.After the CdSe QDs couples with the Ag colloids film,the maximum excitation of CdSe emission shifts from 360nm(on bare glass) to 472 nm(on silver colloids) agreed with the longitudinal dipole mode of silver colloids.This provides a good support to the mechanism of the SPR coupling.Besides,the absorption of silver colloid film is controlled in 358nm～487nm by annealing, meanwhile,the silver colloid films is shown several absorption peaks by tuning the morphologies.3.The nano Au are coupling with nano CdSe in two methods,including layers and dispersal.The PL enhancement and quenching are observed in the two coupling methods.The results indicate that the PL intensity of CdSe QDs is quenched about 02～0.3 times when deposited on the layer of Au/PMMA or Au/SiO₂ compound film with 27nm in Au diameter.What's more,the PL intensity of CdSe QDs with emission wavelengths at 523nm and 595nm are both quenched at about 0.2 times when deposited on the Au film with absorbance peak on 525nm.This proves that is not the the PL quenching is not only induced by fluorescence resonance energy transfer(FRET).As the Au NPs dispersed in the CdSe QDs solutions with Au@ SiO 2 structures,however,the PL intensity of the CdSe QDs is enhanced 1.7.The result also shows that the enhancement factor is related to the combination ratio.The research in this chapter is benefit for the optimization of the size and coupling of the metal NPs in SPR enhanced PL.