Coupling Quantum Emitters and Plasmonic Nanocavities for Energy Transfer and Lasing

Weijia Wang

doi:https://doi.org/10.21985/N2ZF46

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Coupling Quantum Emitters and Plasmonic Nanocavities for Energy Transfer and Lasing

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Plasmonic nanocavities consisting of metal nanoparticle (NP) arrays support surface lattice resonances (SLR) or lattice plasmon, emerged as an exciting platform for manipulating light-matter interactions at the nanoscale. Their recent prominence can be attributed to a combination of desirable photonic and plasmonic characteristics: high electromagnetic field enhancements extended over large volumes with long-lived lifetimes. Chapter I provides an overview on design rules for achieving high-quality optical responses from metal nanoparticle arrays, nanofabrication advances that have enabled their production, and the theory that inspired their experimental realization. Rich fundamental insights will focus on weak and strong coupling with molecular excitons as well as semiconductor excitons and the lattice resonances. As another powerful application of SLR, lattice plasmon lasers will be discussed in detail on theoretical modeling and experimental characterization. Finally, prospects and questions will be discussed. This thesis is mainly focused on ultrafast dynamics of lattice plasmon coupling with excitons in various light emitting materials. In Chapter II, we used metal NP arrays in square lattice as plasmonic nanocavities for lasing action. Cold cavity lifetime measurements showed picosecond scale lifetime of lattice plasmon, indicating their long-range scattering feature. In contrast to the femtosecond lifetime of surface plasmons, lattice plasmons can dramatically slow down the group velocity of light and enable significant optical feedback for stimulated emission. We also identified amplified spontaneous emission (ASE) as an energy transfer channel co-existing with lasing in periodic laser cavities. Side-by-side spectral and temporal investigation on ASE and lasing reveal how coherence of stimulated emission builds up in the system. In Chapter III, we introduce a new lattice geometry that sustains dual-mode SLR. This provides a platform for investigating self-selective exciton-plasmon coupling under the influence of two lattice plasmons with spatially distinct nano-optical field enhancement. We fabricated and characterized optical properties of NPs arranged in rectangular lattice. FDTD simulations showed that the dual-mode SLR has two orthogonal dipolar field enhancement distributions. With organic dye molecules as gain medium, switchable dual-mode lasing with clear threshold behavior and identical plasmonic lasing dynamics was investigated. The dual-mode lasing does not have mode competition which could be applied for on-chip multiplexing. Besides changing the plasmonic nanocavity design, we also explore the new selection of quantum emitters that can interact with lattice plasmons. Chapter IV and Chapter V introduce two types of new emitters: metal-organic frameworks (MOFs) and colloid quantum dots (QDs). Transient absorption measurements characterized the formation of hybrid exciton-plasmon modes in (MOF) conformally coated around plasmonic nanoparticle arrays, which led to mode splitting in spectra. The splitting energy of the modes could be tailored by the detuning of SLR in different index-environments from a single nanostructured materials system. We also demonstrated mode splitting in photoluminescence, that contributed to the faster recombination from the electrons in the hybrid states. Strong enhancement of the emission, over 16-times stronger than that of the pristine Zn-porphyrin, was achieved. Our results established MOFs as a type of molecular emitter materials with great promise to couple with plasmonic nanostructures for energy exchange and transfer. QDs are proposed to serve as gain medium in the prototype of plasmonic lasers. However, few reported on achieving plasmonic lasing with QDs, due to non-radiative process in QDs hindering their application in lasing applications. Chapter V demonstrates a new type of biaxial strained QDs that enables the plasmonic lasing actions. Specifically, the QD plasmonic lasing emission was investigated through light-light curve and showed a decrease of lasing threshold compared to waveguide structure. Time-resolved emission dynamics also exhibited the typical rising time feature in plasmonic systems, indicating the ultrafast energy transfer process. Material dependence study further confirm that the plasmonic component of the SLR was attributing to lasing actions.

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