Electrochemical Control of Strong Coupling of CdSe Exciton-Polaritons in Plasmonic Cavities.

This work reports in situ (active) electrochemical control over the coupling strength between semiconducting nanoplatelets and a plasmonic cavity. We found that by applying a reductive bias to an Al nanoparticle lattice working electrode the number of CdSe nanoplatelet emitters that can couple to the cavity is decreased. Strong coupling can be reversibly recovered by discharging the lattice at oxidative potentials relative to the conduction band edge reduction potential of the emitters. By correlating the number of electrons added or removed with the measured coupling strength, we identified that loss and recovery of strong coupling are likely hindered by side processes that trap and/or inhibit electrons from populating the nanoplatelet conduction band. These findings demonstrate tunable, external control of strong coupling and offer prospects to tune selectivity in chemical reactions.

Liquid lasing from solutions of ligand-engineered semiconductor nanocrystals.

Semiconductor nanocrystals (NCs) can function as efficient gain materials with chemical versatility because of their surface ligands. Because the properties of NCs in solution are sensitive to ligand-environment interactions, local chemical changes can result in changes in the optical response. However, amplification of the optical response is technically challenging because of colloidal instability at NC concentrations needed for sufficient gain to overcome losses. This paper demonstrates liquid lasing from plasmonic lattice cavities integrated with ligand-engineered CdZnS/ZnS NCs dispersed in toluene and water. By taking advantage of calcium ion-induced aggregation of NCs in aqueous solutions, we show how lasing threshold can be used as a transduction signal for ion detection. Our work highlights how NC solutions and plasmonic lattices with open cavity architectures can serve as a biosensing platform for lab-on-chip devices.

Far-field coupling between moiré photonic lattices.

Superposing two or more periodic structures to form moiré patterns is emerging as a promising platform to confine and manipulate light. However, moiré-facilitated interactions and phenomena have been constrained to the vicinity of moiré lattices. Here we report on the observation of ultralong-range coupling between photonic lattices in bilayer and multilayer moiré architectures mediated by dark surface lattice resonances in the vertical direction. We show that two-dimensional plasmonic nanoparticle lattices enable twist-angle-controlled directional lasing emission, even when the lattices are spatially separated by distances exceeding three orders of magnitude of lattice periodicity. Our discovery of far-field interlattice coupling opens the possibility of using the out-of-plane dimension for optical manipulation on the nanoscale and microscale.

Lasing Action from Quasi-Propagating Modes.

Band edges at the high symmetry points in reciprocal space of periodic structures hold special interest in materials engineering for their high density of states. In optical metamaterials, standing waves found at these points have facilitated lasing, bound-states-in-the-continuum, and Bose-Einstein condensation. However, because high symmetry points by definition are localized, properties associated with them are limited to specific energies and wavevectors. Conversely, quasi-propagating modes along the high symmetry directions are predicted to enable similar phenomena over a continuum of energies and wavevectors. Here, quasi-propagating modes in 2D nanoparticle lattices are shown to support lasing action over a continuous range of wavelengths and symmetry-determined directions from a single device. Using lead halide perovskite nanocrystal films as gain materials, lasing is achieved from waveguide-surface lattice resonance (W-SLR) modes that can be decomposed into propagating waves along high symmetry directions, and standing waves in the orthogonal direction that provide optical feedback. The characteristics of the lasing beams are analyzed using an analytical 3D model that describes diffracted light in 2D lattices. Demonstrations of lasing across different wavelengths and lattice designs highlight how quasi-propagating modes offer possibilities to engineer chromatic multibeam emission important in hyperspectral 3D sensing, high-bandwidth Li-Fi communication, and laser projection displays.

Light-Matter Interactions in Hybrid Material Metasurfaces.

This Review focuses on the integration of plasmonic and dielectric metasurfaces with emissive or stimuli-responsive materials for manipulating light-matter interactions at the nanoscale. Metasurfaces, engineered planar structures with rationally designed building blocks, can change the local phase and intensity of electromagnetic waves at the subwavelength unit level and offers more degrees of freedom to control the flow of light. A combination of metasurfaces and nanoscale emitters facilitates access to weak and strong coupling regimes for enhanced photoluminescence, nanoscale lasing, controlled quantum emission, and formation of exciton-polaritons. In addition to emissive materials, functional materials that respond to external stimuli can be combined with metasurfaces to engineer tunable nanophotonic devices. Emerging metasurface designs including surface-functionalized, chemically tunable, and multilayer hybrid metasurfaces open prospects for diverse applications, including photocatalysis, sensing, displays, and quantum information.

Magneto-Fluorescent Perovskite Nanocomposites for Directed Cell Motion and Imaging.

The ability for a magnetic field to penetrate biological tissues without attenuation has led to significant interest in the use of magnetic nanoparticles for biomedical applications. In particular, active research is ongoing in the areas of magnetically guided drug delivery and magnetic hyperthermia treatment. However, the difficulties in tracing these optically nonactive magnetic nanoparticles hinder their usage in medical research or treatment. Here, a new perovskite-based magneto-fluorescent nanocomposite that allows the in situ, real-time optical visualization of magnetically induced cellular movements is reported. A swelling-deswelling technique is employed to capture a cesium lead halide perovskite and magnetite nanoparticles within a biocompatible polyvinylpyrrolidone matrix, to produce a water-dispersible composite that possesses a combination of strong magnetic response and intense fluorescence. The wavelength-tunability of perovskite nanocrystals is taken advantage of to demonstrate simultaneous multicolor fluorescent tagging of cancer stem cells. The magneto-directed motion of the cancer stem cells through a microfluidic channel is also imaged as a proof-of-concept toward an optically traceable magnetic manipulation of biological systems. These dual-functional nanocomposites could find promising applications in advanced biotechnologies, such as in optogenetics, cellular separation, and drug delivery studies.