Plasmon-exciton coupling for enhanced energy conversion

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Bhawna Bagra (Creator)
The University of North Carolina at Greensboro (UNCG )
Web Site:
Jianjun Wei

Abstract: The primary theme of my research is the light-matter interaction that involves plasmon-exciton coupling effect on energy conversion and optical enhancement. Plasmons are collective oscillation of electrons in metal, which leads to concentration of optical fields in the vicinity when coupled with incident light. Excitons are bound states of electron-hole pairs in molecular or semiconductor materials, having size dependent transition optical frequencies and efficient optical emission in specific cases. Plasmon and exciton interact to form a hybridized light-matter state with multitude of potential applications including, enhanced energy conversion or transportation and sensing. However, the interaction of coupling with plasmonic nanoslit is still fragmentary. In particular, previous investigation is mostly based on interaction with the localized surface plasmon resonance (LSPR) modes and studies based on surface plasmon polariton (SPP) are still needs to be explored with the detailed energy transfer mechanism between plasmon and excitons. Furthermore, in comparison with the absorption/scattering spectra of the plasmon-exciton, which is well studied and understood, the emitting properties of exciton due to plasmon-exciton coupling are still unclear. To address these issues, we designed and fabricated the nanoslit structures having both LSPR and SPP plasmon modes and examined the different systems for plasmon-exciton coupling effect. This research work includes understanding of plasmon-exciton coupling of the nanoslit system with immobilized exciton moieties for energy conversion, specifically, light-light energy conversion, light-electric energy conversion and optical sensing of biomolecules. (1) For light-light energy conversion, fluorescence of Carbon Nanodots (CNDs) embedded in the nanoslit arrays is investigated. Two distinct designs are examined for fluorescence of CNDs: the CNDs immobilized in different width gold nanoslits and CNDs coupled gold nanoparticles (Au NPs) hybrids immobilized inside the gold nanoslit. Results demonstrate the enhanced fluorescence of CNDs when placed in nanoslit due to plasmon induced energy transfer to the CNDs. (2) A single nanoslit photoelectrochemical cell with CNDs and TiO2 immobilization is examined for light-electric energy conversion. Enhanced photocurrent generation observed and explained with plasmon-exciton coupling between plasmonic gold nanoslit and CNDs. (3) For sensing, the research investigated a microfluidic dam with plasmonic nanoledge array structure for detection of type 1 diabetes biomarkers. The shift of the plasmon frequency with respect to the refractive index of the surrounding medium utilized as a principle for detection method. In addition to the experimental studies, a semi-analytical model for surface plasmon generation analysis and Finite-difference time-domain (FDTD) method used for simulating and modeling the optical properties from the nanoslit systems, which provides insights into the underlying physics of the plasmon-exciton coupling interactions. We found plasmon-exciton coupling in the nanostructures increases the electromagnetic (EM) field intensity by plasmonic light trapping and plasmon-induced resonance energy transfer (PIRET). This enhanced field corresponds to the modification of excitation and emission rate in exciton which ultimately enhance the energy conversion process. Fundamental understanding of the plasmon-exciton coupling in this work will leads to the applications that includes plasmonic photovoltaic, low threshold laser, ultra-sensitive biosensors, and high efficiency optoelectronic nanodevices.

Additional Information

Language: English
Date: 2021
Biosensors, Carbon nanodots, Fluorescence, Lithography, Plasmon, Plasmonics
Plasmons (Physics)
Lithography, Electron beam
Nanostructured materials

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