Bismuth oxide is an important bismuth compound having applications in electronics, photo-catalysis and medicine. At the nanoscale, bismuth oxide experiences a variety of new physico-chemical properties because of its increased surface to volume ratio leading to potentially new applications. In this manuscript, we report for the very first time the synthesis of bismuth oxide (Bi₂O₃) nano-flakes by pulsed laser ablation in liquids without any external assistance (no acoustic, electric field, or magnetic field). The synthesis was performed by irradiating, pure bismuth needles immerged in de-ionized water, at very high fluence ∼160 J cm⁻² in order to be highly selective and only promote the growth of two-dimensional structures. The x- and y-dimensions of the flakes were around 1 μm in size while their thickness was 47.0 ± 12.7 nm as confirmed by AFM analysis. The flakes were confirmed to be α- and γ-Bi₂O₃ by SAED and Raman spectroscopy. By using this mixture of flakes, we demonstrated that the nanostructures can be used as antimicrobial agents, achieving a complete inhibition of Gram positive (MSRA) and Gram negative bacteria (MDR-EC) at low concentration, ∼50 ppm.

Individual plasmonic film-coupled nanostar resonators exhibit polarized optical modes in ultrasmall volumes, which can be useful for applications in sensing or enhanced light-matter interactions.

Enhanced electromagnetic fields within plasmonic nanocavity mode volumes enable multiple significant effects that lead to applications in both the linear and nonlinear optical regimes. In this work, enhanced second‐harmonic generation (SHG) is demonstrated from individual plasmonic nanopatch antennas (NPAs) which are formed by separating silver nanocubes from a smooth gold film using a sub‐10 nm zinc oxide spacer layer. When the NPAs are excited at their fundamental plasmon frequency, a 10⁴‐fold increase in the intensity of the SHG wave is observed. Moreover, by integrating quantum emitters that have an absorption energy at the fundamental frequency, a second‐order nonlinear exciton–polariton strong coupling response is observed with a Rabi splitting energy of 19 meV. The nonlinear frequency conversion using NPAs thus provides an excellent platform for nonlinear control of the light−matter interactions in both weak and strong coupling regimes which will have a great potential for applications in optical engineering and information processing.

We report an experimental study of the plasmon-assisted spontaneous emission and the Förster resonance energy transfer between organic molecules and semiconductor colloidal quantum dots. The localized plasmonic field in the nanogap between a gold nano-popcorn's tips and a 5-nm separated gold film supports high photonic density of states and provides pathways for the light-matter interaction mechanisms. We demonstrate that, besides the total enhanced decay rate up to 66 times for quantum dots and molecules, the Förster resonance energy transfer efficiency and rate constant are simultaneously modified. While the energy transfer efficiency is reduced from 84% to 35% due to the non-radiative quenching effect and fast donor decay rate, the energy transfer rate constant is significantly increased from 4 to 20 ns⁻¹. Our results have quantitatively elucidated decay mechanisms that are important toward understanding and controlling of the light-matter interaction at the nanoscale.

Plasmonic nanopatch antennas that incorporate dielectric gaps hundreds of picometers to several nanometers thick have drawn increasing attention over the past decade because they confine electromagnetic fields to grossly sub-diffraction-limited volumes. Substantial control over the optical properties of excitons and color centers confined within these plasmonic cavities has already been demonstrated with far-field optical spectroscopies, but near-field optical spectroscopies are essential for an improved understanding of the plasmon–emitter interaction at the nanoscale. Here, we characterize the intensity and phase-resolved plasmonic response of isolated nanopatch antennas by cathodoluminescence microscopy. Furthermore, we explore the distinction between optical and electron beam spectroscopies of coupled plasmon–exciton heterostructures to identify constraints and opportunities for future nanoscale characterization and control of hybrid nanophotonic structures. While we observe substantial Purcell enhancement in time-resolved photoluminescence spectroscopies, negligible Purcell enhancement is observed in cathodoluminescence spectroscopies of hybrid nanophotonic structures. The substantial differences in measured Purcell enhancement for electron beam and laser excitation can be understood as a result of the different selection rules for these complementary experiments. These results provide a fundamentally new understanding of near-field plasmon–exciton interactions in nanopatch antennas, which is essential for myriad emerging quantum photonic devices.