Tuning Emission Of Quantum Dots By Modes Of Surface Plasmons Of Silver Nanorod Arrays

Tuning emission wavelength of quantum dots has important applications in many fields such as laser,display and sensing.The emission wavelength of quantum dots can be adjusted by changing the structure,the external environment and coupling with photonic structures.Although the traditional dielectric cavities in photonic structures have high quality factors,the mode volume is large.Metal nanostructures without the diffraction limit exhibit very small mode volumes.It has been reported that a wavelength-tunable emission is achieved by coupling disordered metal nanoparticles or metal nanoparticle arrays to quantum dots.In this thesis,we developed a method to fabricate micro-nano structures,the fluorescence enhancement and emission wavelength were modulated based on the coupling between silver nanorod arrays and quantum dots,which has potential applications in fluorescence labeling and light-emitting display.The main contents and results of this thesis are as follows:(1)Fabrication of silver nanorod arrays and investigation of surface plasmon resonant cavity modes.The anodic aluminium oxide(AAO)templates were first prepared by oxidation two-step anodization method and then the silver nanorod arrays were electrodeposited in the nanochannels of the AAO templates,and different lengths of the silver nanorod arrays were obtained by control of the electrodeposition time.Furthermore,the reflectance spectra of the silver nanorod arrays were measured by a ultraviolet-visible-near-infrared spectrophotometer,and it was found that the silver nanorod arrays had multi-order longitudinal plasmonic resonant modes,and the number of modes increases with the increase of the nanorod length,the resonance wavelength of the same order modes present a redshift.A finite time domain difference(FDTD)method was used to simulate the surface plasmonic resonant modes of the silver nanorod arrays,which was basically consistent with the experimental results.In addition,the silver nanorod arrays perform the plasmonic resonant cavity modes,and their longitudinal modes have very strong localized electric fields with standing wave modes.Different order resonant cavity modes correspond to different numbers of standing wave wavelengths.(2)Preparation of coupling structures of silver nanorod arrays and CdSe/ZnS quantum dots,modulation of fluorescence emission by the thickness of the dielectric layer.The coupling structures of silver nanorod arrays and CdSe/ZnS quantum dots were prepared by design of a spacer layer of PMMA film.Measurements of the fluorescence spectra indicate that the thickness of the PMMA spacer layer had a significant effect on the emission intensity of the coupling structures,it is found that the emission intensity of the coupling structures first increases and then decreases with increasing the thickness of the PMMA spacer layer,the emission intensity of the coupling structures reaches the maximum value for a 20 nm thick spacer layer,which indicates the strongest coupling effect between the plasmonic resonant modes of the silver nanorod arrays and the fluorescence emission of the quantum dots appears.(3)Modulation of the emission wavelength of quantum dots by plasmonic resonant cavity modes of the silver nanorod arrays.A light emission with a FWHM of 5-6 nm was achieved by coupling the silver nanorod arrays to CdSe/ZnS quantum dots,that the FWHM of coupling structure was narrower than that of the pure CdSe/ZnS quantum dots(FWHM was 28 nm),because energy transfer occurs when the emission spectrum of quantum dots overlaps with the plasmonic resonant mode of the silver nanorod arrays,that is,the excitons generated by the excitation of the quantum dots are transferred to the surface plasmons of the silver nanorod arrays with a non-radiative form,as well as the strong localized electric fields of the silver nanorod arrays result in the narrow emission spectrum of the coupling structures.Furthermore,the emission wavelength of the quantum dots can be tuned in a wide spectral range of 646 nm-670 nm by the different modes of the plasmonic resonant cavities.