Selective Flocculation and H2O2-Free Oxidative Etching-Based Synthesis of Highly Monodisperse Ag Nanospheres for Uniform Quantum Dot Photoluminescence-Enhancing Plasmonic Cavity Applications.

Ag nanoparticles have garnered significant attention for their excellent plasmonic properties and potential use as plasmonic cavities, primarily because of their intrinsically low ohmic losses and optical properties in the visible range. These are particularly crucial in systems involving quantum dots that absorb light at low wavelengths, where the need for a high threshold energy of interband transitions necessitates the incorporation of Ag nanostructures. However, the synthesis of Ag nanoparticles still encounters challenges in achieving structural uniformity and monodispersity, along with chemical stability, consequentially inducing inconsistent and poorly reliable optical responses. Here, we present a two-step approach for synthesizing highly uniform spherical Ag nanoparticles involving depletion-induced flocculation and Cu(II)-mediated oxidative etching. We found that the selective flocculation of multitwinned Ag nanocrystals significantly enhances the uniformity of the resulting Ag nanostructures, leaving behind only single-crystalline and single-twinned nanostructures. Subsequent oxidative etching, in which cupric ions are directly involved in the reaction, was designed based on Pourbaix diagrams to proceed following thermodynamically favorable states and circumvent the generation of reactive chemical species such as H2O2. This leads to perfectly spherical shapes of final Ag nanoparticles with a synthetic yield of 99.5% and additionally reduces the overall reaction time. Furthermore, we explore the potential applications of these monodisperse Ag nanospheres as uniform plasmonic cavities. The fabricated Ag nanosphere films uniformly enhanced the photoluminescence of InP/ZnSe/ZnS quantum dots, showcasing their capabilities in exhibiting consistent plasmonic responses across a large area.

One-Pot Heterointerfacial Metamorphosis for Synthesis and Control of Widely Varying Heterostructured Nanoparticles.

Despite remarkable facileness and potential in forming a wide variety of heterostructured nanoparticles with extraordinary compositional and structural complexity, one-pot synthesis of multicomponent heterostructures is largely limited by the lack of fundamental mechanistic understanding, designing principles, and well-established, generally applicable chemical methods. Herein, we developed a one-pot heterointerfacial metamorphosis (1HIM) method that allows heterointerfaces inside a particle to undergo multiple equilibrium stages to form a variety of highly crystalline heterostructured nanoparticles at a relatively low temperature (<100 °C). As proof-of-concept experiments, it was shown that widely different single-crystalline semiconductor-metal anisotropic nanoparticles with synergistic chemical, spectroscopic, and band-gap-engineering properties, including a series of metal-semiconductor nanoframes with high structural and compositional tunability, can be formed by using the 1HIM approach. 1HIM offers a new paradigm to synthesize previously unobtainable or poorly controllable heterostructures with unique or synergistic properties and functions.

Quantitative Nanoplasmonics.

Plasmonics, the study of the interactions between photons and collective oscillations of electrons, has seen tremendous advances during the past decade. Controllable nanometer- and sub-nanometer-scale engineering in plasmonic resonance and electromagnetic field localization at the subwavelength scale have propelled diverse studies in optics, materials science, chemistry, biotechnology, energy science, and various applications in spectroscopy. However, for translation of these accomplishments from research into practice, major hurdles including low reproducibility and poor controllability in target structures must be overcome, particularly for reliable quantification of plasmonic signals and functionalities. This Outlook introduces and summarizes the recent attempts and findings of many groups toward more quantitative and reliable nanoplasmonics, and discusses the challenges and possible future directions.