Multiphoton Emission Enhancement from a Single Colloidal Quantum Dot Using SiO2-Coated Silver Nanoparticles

Single-Photon Emission from Organic Dye Molecules Adsorbed on a Quantum Dot via Energy Transfer

Single-photon emissions from individual emitters are crucial in fundamental science and quantum information technologies. Multichromophoric systems, comprising multiple dyes, can exhibit single-photon emissions through efficient annihilation between the excited states; however, exploring this phenomenon in complex systems remains a challenge. In this study, we investigated the photon statistics of emissions from multiple perylene bisimide (PBI) dyes adsorbed onto the surface of CdSe/ZnS quantum dots (QDs). When multiple PBIs were simultaneously excited by both direct excitation and energy transfer from the QD, multiphoton emissions from the PBIs were observed. Conversely, when the QDs were selectively excited, multiple PBIs exhibiting single-photon emission through energy transfer from the QDs to the PBIs were found. These results highlight the intriguing interplay between multichromophoric systems and QDs, offering valuable insights into the development of efficient single-photon sources in quantum information technologies.

Recent update on antibacterial and antifungal activity of quinoline scaffolds

Although most of the heterocycles have been reported to possess a significant pharmacological activity, only a few of them, namely quinoline derivatives, have exhibited the finest biological activities. Despite the few medicinal properties of the plain quinoline molecule, its derivatives exhibit diverse pharmacological properties such as anticancer, anti-inflammatory, antibacterial, antiviral, antifungal, antiprotozoal activities, and so on. The potential antimicrobial properties of the quinoline derivatives are evident from the decades of research on these derivatives. Owing to limitations like drug resistance, high cost, severe side effects, and less bioavailability of previously synthesized antimicrobial agents, these drugs have become obsolete in recent years. Hence, the design of more efficient antimicrobial drugs must be given topmost priority. A breakthrough in drug discovery is a must to prevent malevolent microbial diseases. Addressing all these issues, researchers have been continuously contributing to antimicrobial drug discovery. Herein, a short description of the pharmacology of antimicrobial agents such as antibacterials and antifungals synthesized recently is provided. The versatile derivatization of the quinoline moiety leading to significant antimicrobial potencies is discussed, considering the structure-activity relationship.

In Situ Observation of Emission Behavior during Anion-Exchange Reaction of a Cesium Lead Halide Perovskite Nanocrystal at the Single-Nanocrystal Level

Postsynthesis anion-exchange reaction of cesium lead halide (CsPbX₃; X = Cl, Br, and I) perovskite nanocrystals (NCs) has emerged as a unique strategy to control band gap. Recently, the partially anion-exchanged CsPb(Br/I)₃ NC was reported to form an inhomogeneously alloyed heterostructure, which could possibly form some emission sites depending on the halide composition in the single NC. In this work, we observed the in situ emission behavior of single CsPb(Br/I)₃ NCs during the anion-exchange reaction. Photon-correlation measurements of the single NCs revealed that the mixed halide CsPb(Br/I)₃ NC exhibited single-photon emission. Even when irradiated with an intense excitation laser, the single NC exhibited single-photon emission with a photoluminescence spectrum of a single peak. These results suggested that the heterohalide compositions of the CsPb(Br/I)₃ NC do not form any emission sites with different band gap energies; instead, the NC forms emission sites with uniform band gap energy as a whole NC via quantum confinement.

Enhancement of Biexciton Emission Due to Long-Range Interaction of Single Quantum Dots and Gold Nanorods in a Thin-Film Hybrid Nanostructure

Semiconductor quantum dots (QDs) are known for their ability to exhibit multiphoton emission caused by recombination of biexcitons (BX). However, the quantum yield (QY) of BX emission is low due to the fast Auger process. Plasmonic nanoparticles (PNPs) provide an attractive opportunity to accelerate BX radiative recombination. Here, we demonstrate the PNPs induced distance-controlled enhancement of BX emission of single QDs. Studying the same single QD before and after its integration with the PNPs, we observed a plasmon-mediated increase in the QY of BX emission. Remarkably, the enhancement of BX emission remains pronounced even at distances of 170 nm. We attribute this effect to efficient coupling, which results in the trade-off between resonance energy transfer from QD to gold nanorods and the Purcell effect at small QD-PNP separations and the predominant influence of the Purcell effect at longer distances. Our findings constitute a reliable approach to managing the efficiency of multiexciton emission over a wide span of distances, thus paving the way for new applications.

Colloidal Quantum Dot Arrangement Assisted by Perylene Bisimide Self-Assembly

Colloidal semiconductor nanocrystals, so-called quantum dots (QDs), are attractive as molecular-like smart nanomaterials, and their emission and optoelectronic properties in the dispersed state have been actively studied. The construction of supramolecular structures composed of multiple QDs, however, is still challenging. Here, a new strategy to form supramolecular QD structures via self-assembly of perylene bisimide (PBI) dyes is demonstrated. In a mixed solution, QDs and PBI undergo time-dependent fusion to form an isolated colloidal QD-PBI complex or a unique QD-PBI co-aggregate composed of QDs arranged along a sheet-like PBI nanostructure, and these dramatically different supramolecular structures can be controlled by the solvent polarity.

Excitation wavelength dependent photon anti-bunching/bunching from single quantum dots near gold nanostructures

In this study, we aim to investigate the change in photon emission statistics of single CdSe/CdS core/shell quantum dots (QDs) on dielectric modified gold nanoparticle (NP) substrates as a function of the excitation wavelength. Photons emitted from single QDs are typically "anti-bunched" and are independent of the excitation wavelength. However, when QDs are coupled to plasmonic substrates, even at the low excitation power regime, we observed a significant change in photoluminescence emission behavior of single QDs; i.e. the emission transformed from incomplete photon anti-bunched to bunched when the excitation was changed from "off" to "on" plasmon resonance. Theoretical studies based on electrodynamics modeling suggested that for the QD-Au NP system, the quantum yield of single excitons decreases while that of biexcitons increases. In addition, when excited at the "on" resonance condition, the absorption is highly enhanced, resulting in an increased population of higher order excitons of the QDs. The higher order exciton emission was directly observed as an additional peak appeared at the blue side of the exciton peak of single QDs. The combined effect of the change in quantum yield and the increase in the absorption cross-section switches the photons emitted by single QDs from anti-bunched to bunched. These results provided direct evidence that not only the plasmonic nanostructures but also the excitation wavelength can effectively control the photon emission statistics of single QDs in the hybrid metal-semiconductor system. Manipulating the multiexciton-plasmon interaction in a hybrid complex like this could possibly open up new doors for applications such as entangled photon pair generation and plasmon-enhanced optoelectronic devices.