Effects of Plasmon-Exciton Coupling on the Optical Properties of CdSe/Zns Quantum Dots Coupled to Gold Nanoparticles
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1208-O16-04
Effects of Plasmon-Exciton Coupling on the Optical Properties of CdSe/Zns Quantum Dots Coupled to Gold Nanoparticles S. G. Chou, H. G. Kang, M. L. Clarke, J. Hwang Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, MD20899 ABSTRACT By using a multi-color, multi-modal imaging platform, we look into the effects of excitonplasmon coupling on optical properties of a semiconductor quantum dot (QD) that is coupled to a nearby gold NP nanoparticle (AuNP). By exciting this coupled material with laser excitation energies that are either strongly or weakly resonating with the plasmon resonance of the AuNP, the effects of plasmon-exciton coupling was studied by analyzing the changes in the photoluminescence signal, the photoluminescence lifetime, and the blinking pattern of the QD. INTRODUCTION Nanoplasmonics has been a rapidly advancing field for its diverse array of applications in photonics and biotechnology. By manipulating the generation and transmission of surface plasmons, a nanoparticle can generate a highly localized field to enhance the optical signal from molecules in its proximity or to channel energy into desired locations. In particular, the photophysical interactions between semiconductor quantum dots (QDs) and metallic nanoparticles (NPs) at the single particle level have been studied intensely[1-8]. A better understanding of the localized energy transfer and surface plasmon-exciton interaction between a QD and a metallic NP would aid the efforts to control and improve the desired optical properties of the QD such as suppressed blinking and single photon generation[6-9]. Even though plasmon-exciton coupling at the single QD molecule level has been previously studied[6-8], the optical studies have usually involved NPs with a wide plasmon resonance window to ensure that the plasmons and excitons are excited simultaneously with a single excitation energy. In this study, we monitored the optical properties of a QD that is coupled to a nearby AuNP with a relatively narrow yet well defined plasmon resonance window. By selectively exciting the coupled system with laser excitation energies both on and off the peak plasmon resonance frequency of the metallic NPs while continuously monitoring the optical signal from the QD, we study the possible effects of the strength of the localized plasmonic field on the QD exciton. EXPERIMENT: Sample Preparation: The samples were first prepared by drop-casting 20 microliters of spherical 50 nm gold nanoparticle (AuNP) solution (4.5 x 1010 particles/ml, Ted Pella) onto an ozone plasma-cleaned glass cover slip. The distribution of AuNPs was characterized using polarized light microscopy. Once the desired concentration and distribution of AuNPs was achieved, 20 microliters of 30 nmol/L CdSe/ZnS QD solution (Invitrogen) was drop-cast onto the same glass coverslip. Optical Measurements:
471nm pulsed laser for life-time measurements
Samp le
532nm cw laser excitation
1.45 NA oil objective Dichroic filter
shutter 520nm long pass fil
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