Effects of Pressure on Exciton Absorption and Emission in Strongly Quantum-Confined CsPbBr Quantum Dots and Nanoplatelets.

Soft lattices of metal halide perovskite (MHP) nanocrystals (NCs) are considered responsible for many of their optical properties associated with excitons, which are often distinct from other semiconductor NCs. Earlier studies of MHP NCs upon compression revealed how structural changes and the resulting changes in the optical properties such as the bandgap can be induced at relatively low pressures. However, the pressure response of the exciton transition itself in MHP NCs remains relatively poorly understood due to limitations inherent to studying weakly or nonconfined NCs in which exciton absorption peaks are not well-separated from the continuum interband transition.

Defect-Passivated Photosensor Based on Cesium Lead Bromide (CsPbBr) Perovskite Quantum Dots for Microbial Detection.

A defect-passivated photosensor based on cesium lead bromide (CsPbBr) perovskite quantum dots (QD) was fabricated using parylene films, and the photosensor was applied for the microbial detection. The CsPbBr perovskite QDs were synthesized to be homogeneous in size under thermodynamic control, and the perovskite QD-based photosensor was fabricated using MoS flakes as the electron transfer layer. In this work, a parylene film with functional groups was deposited on a photosensor for physical protection (waterproof) and defect (halide vacancy) passivation of the perovskite QD.

Wearable fabric-based ZnO nanogenerator for biomechanical and biothermal monitoring.

Wearable devices that can mechanically conform to human skin are a necessity for reliable monitoring and decoding of biomechanical activities through skin. Most inorganic piezoelectrics, however, lack deformability and damage tolerance, impeding stable motion monitoring. Here, we present an air-permeable fabric-based ZnO nanogenerator with mechanical adaptivity to diverse deformations for wearable piezoelectric sensors, collecting biomechanical health data.

Effects of hole transporting PEDOT:PSS on the photoemission of upconverted hot electron in Mn-doped CdS/ZnS quantum dots.

In this work, we investigated the effect of hole transporting poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) interfacing with Mn-doped CdS/ZnS quantum dots (QDs) deposited on an indium tin oxide (ITO) substrate on the photoemission of upconverted hot electrons under weak continuous wave photoexcitation in a vacuum. Among the various factors that can influence the photoemission of the upconverted hot electrons, we studied the role of PEDOT:PSS in facilitating the hole transfer from QDs and altering the energy of photoemitted hot electrons. Compared to hot electrons emitted from QDs deposited directly on the ITO substrate, the addition of the PEDOT:PSS layer between the QD and ITO layers increased the energy of the photoemitted hot electrons.

Laser-Shock-Driven Evolution of Atomic Defect and Piezoelectricity in Graphitic Carbon Nitride for the Ionization in Mass Spectrometry.

Nanostructures─coupled with mass spectrometry─have been intensively investigated to improve the detection sensitivity and reproducibility of small biomolecules in laser desorption/ionization mass spectrometry (LDI-MS). However, the impact of laser-induced shock wave on the ionization of the nanostructures has rarely been reported. Herein, we systematically elucidate the laser shock wave effect on the ionization in terms of the development of atomic defects and piezoelectricity in two-dimensional graphitic carbon nitride nanosheets (g-CN NS) by short laser pulses.

Photoemission of the Upconverted Hot Electrons in Mn-Doped CsPbBr Nanocrystals.

Hot electrons play a crucial role in enhancing the efficiency of photon-to-current conversion or photocatalytic reactions. In semiconductor nanocrystals, energetic hot electrons capable of photoemission can be generated via the upconversion process involving the dopant-originated intermediate state, currently known only in Mn-doped cadmium chalcogenide quantum dots. Here, we report that Mn-doped CsPbBr nanocrystals are an excellent platform for generating hot electrons via upconversion that can benefit from various desirable exciton properties and the structural diversity of metal halide perovskites (MHPs).

One-Step Homogeneous Immunoassay for the Detection of Influenza Virus Using Switching Peptide and Graphene Quencher.

One-step homogeneous immunoassay was developed for detecting influenza viruses A and B (Inf-A and Inf-B) using the switching peptide H2. As the fluorescence-labeled switching peptide dissociated from the binding pocket of detection antibodies, the fluorescence signal could be directly generated by the binding of Inf-A and Inf-B without washing (i.e.

Active Tuning of Plasmon Damping via Light Induced Magnetism.

Circularly polarized optical excitation of plasmonic nanostructures causes coherent circulating motion of their electrons, which in turn gives rise to strong optically induced magnetization, a phenomenon known as the inverse Faraday effect (IFE). In this study we report how the IFE also significantly decreases plasmon damping. By modulating the optical polarization state incident on achiral plasmonic nanostructures from linear to circular, we observe reversible increases of reflectance by up to 8% and simultaneous increases of optical field concentration by 35.

Magnetic Effect of Dopants on Bright and Dark Excitons in Strongly Confined Mn-Doped CsPbI Quantum Dots.

We investigated the magnetic effect of Mn ions on an exciton of Mn-doped CsPbI quantum dots (QDs), where we looked for the signatures of an exciton magnetic polaron known to produce a large effective magnetic field in Mn-doped CdSe QDs. In contrast to Mn-doped CdSe QDs that can produce ∼100 T of magnetic field upon photoexcitation, manifested as a large change in the energy and relaxation dynamics of a bright exciton, Mn-doped CsPbI QDs exhibited little influence of a magnetic dopant on the behavior of a bright exciton. However, a μs-lived dark exciton in CsPbI QDs showed 40% faster decay in the presence of Mn, equivalent to the effect of ∼3 T of an external magnetic field.

Deflection Estimation Based on the Thermal Characteristics of Composite Deck Slabs Containing Macro-Synthetic Fibers.

The purpose of this study was to evaluate the structural performance of composite deck slabs containing macro-synthetic fibers. after a fire by proposing a deflection estimation method for non-fireproof structural decks. Therefore, this study evaluated the fire resistance performance and deflection of deck slabs mixed with macro-synthetic fibers.

Efficient Redox-Neutral Photocatalytic Formate to Carbon Monoxide Conversion Enabled by Long-Range Hot Electron Transfer from Mn-Doped Quantum Dots.

Energetic hot electrons generated in Mn-doped quantum dots (QDs) via exciton-to-hot-electron upconversion possess long-range transfer capability. The long-range hot electron transfer allowed for superior efficiency in various photocatalytic reduction reactions compared to conventional QDs, which solely rely on the transfer of band edge electrons. Here we show that the synergistic action of the interfacial hole transfer to the initial reactant and subsequent long-range hot electron transfer to an intermediate species enables highly efficient photocatalytic reactions, thereby extending the benefits of Mn-doped QDs beyond reduction reactions.

Cesium Lead Bromide (CsPbBr) Perovskite Quantum Dot-Based Photosensor for Chemiluminescence Immunoassays.

Chemiluminescence immunoassays have been widely employed for diagnosing various diseases. However, because of the extremely low intensity chemiluminescence signals, highly sensitive transducers, such as photomultiplier tubes and image sensors with cooling devices, are required to overcome this drawback. In this study, a hypersensitive photosensor was developed based on cesium lead bromide (CsPbBr) perovskite quantum dots (QDs) with sufficient high sensitivity for chemiluminescence immunoassays.

State of the Art and Prospects for Halide Perovskite Nanocrystals.

Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications.

Synthesis and Properties of Strongly Quantum-Confined Cesium Lead Halide Perovskite Nanocrystals.

ConspectusSemiconducting metal halide perovskite (MHP) nanocrystals have emerged as an important new class of materials as the source of photons and charges for various applications that can outperform many other semiconductor nanocrystals utilized for the same purposes. However, the majority of the studies of MHP nanocrystals focused on weakly or nonconfined systems, where the quantum confinement giving rise to various size-dependent and confinement-enhanced photophysical properties cannot be explored readily. This was partially due to the challenge in producing strongly quantum-confined MHP nanocrystals, since the traditional kinetic control approach was less effective for the size control.

Size-dependent dark exciton properties in cesium lead halide perovskite quantum dots.

The fine structure of the band edge exciton and the dark exciton photoluminescence (PL) are topics of significant interest in the research of semiconducting metal halide perovskite nanocrystals, with several conflicting reports on the level ordering of the bright and dark states and the accessibility of the emitting dark states. Recently, we observed the intense dark exciton PL in strongly confined CsPbBr nanocrystals at cryogenic temperatures, in contrast to weakly confined nanocrystals lacking dark exciton PL, which was explained by the confinement enhanced bright-dark exciton splitting. In this work, we investigated the size-dependence of the dark exciton photoluminescence properties in CsPbBr and CsPbI quantum dots in the strongly confined regime, showing the clear role of confinement in determining the bright-dark energy splitting (ΔE) and the dark exciton lifetime (τ).

Intense Dark Exciton Emission from Strongly Quantum-Confined CsPbBr Nanocrystals.

Dark exciton as the lowest-energy (ground) exciton state in metal halide perovskite nanocrystals is a subject of much interest. This is because the superior performance of perovskites as the photon source combined with long lifetime of dark exciton can be attractive for many applications of exciton. However, the direct observation of the intense and long-lived dark exciton emission, indicating facile access to dark ground exciton state, has remained elusive.

Size- and temperature-dependent photoluminescence spectra of strongly confined CsPbBr quantum dots.

Lead-halide perovskite nanocrystals (NCs) are receiving much attention as a potential high-quality source of photons due to their superior luminescence properties in comparison to other semiconductor NCs. To date, research has focused mostly on NCs with little or no quantum confinement. Here, we measured the size- and temperature-dependent photoluminescence (PL) from strongly confined CsPbBr quantum dots (QDs) with highly uniform size distributions, and examined the factors determining the evolution of the energy and linewidth of the PL with varying temperature and QD size.

On the determination of absorption cross section of colloidal lead halide perovskite quantum dots.

The absorption cross section of lead halide perovskite nanocrystals is important for understanding their photophysical properties, especially those depending on the density of photoexcited charge carriers. Despite its importance, there are large discrepancies among the reported absorption cross section values determined employing different methods. Here, we measured the absorption cross section of CsPbBr quantum dots (QDs) of varying sizes using elemental analysis and transient absorption (TA) saturation methods and compared with the previously reported values determined from elemental analysis and transient photoluminescence (PL) saturation methods.

Energetic hot electrons from exciton-to-hot electron upconversion in Mn-doped semiconductor nanocrystals.

Generation of hot electrons and their utilization in photoinduced chemical processes have been the subjects of intense research in recent years mostly exploring hot electrons in plasmonic metal nanostructures created via decay of optically excited plasmon. Here, we present recent progress made in generation and utilization of a different type of hot electrons produced via biphotonic exciton-to-hot electron "upconversion" in Mn-doped semiconductor nanocrystals. Compared to the plasmonic hot electrons, those produced via biphotonic upconversion in Mn-doped semiconductor nanocrystals possess much higher energy, enabling more efficient long-range electron transfer across the high energy barrier.

Photoinduced Mn doping in cesium lead halide perovskite nanocrystals.

We report the photoinduced post-synthesis method of Mn doping in colloidal perovskite nanocrystals, which can produce Mn-doped CsPbX3 (X = Cl, Br) nanocrystals with preserved size and anisotropic morphology. Photoinduced Mn doping occurs through cation exchange driven by the facile photoinduced halide exchange in dihalomethane (CH2X2, X = Cl, Br) solvent taking advantage of in situ photogeneration of halide ions from the solvent molecules. In the presence of a small amount of Mn acetate dissolved in solvent at sub-micromolar concentration, photoexcitation of the nanocrystals above the bandgap initiates the simultaneous anion and cation exchange.

Light-Induced Activation of Forbidden Exciton Transition in Strongly Confined Perovskite Quantum Dots.

We report the strong light-induced activation of forbidden exciton transition in CsPbBr perovskite quantum dots mediated by the symmetry-breaking polaron that modifies the optical selection rule of the confined exciton transition. The activated forbidden transition results in an intense pump-induced absorption in the transient absorption spectra above the bandgap, where the original parity-forbidden transition was located. In contrast to many other semiconductor quantum dots, photoexcitation of an exciton in CsPbBr quantum dots creates a sufficiently large perturbation via a lattice-distorting polaron, which turns on the formally forbidden transition.

Precise Control of Quantum Confinement in Cesium Lead Halide Perovskite Quantum Dots via Thermodynamic Equilibrium.

Cesium lead halide (CsPbX) nanocrystals have emerged as a new family of materials that can outperform the existing semiconductor nanocrystals due to their superb optical and charge-transport properties. However, the lack of a robust method for producing quantum dots with controlled size and high ensemble uniformity has been one of the major obstacles in exploring the useful properties of excitons in zero-dimensional nanostructures of CsPbX. Here, we report a new synthesis approach that enables the precise control of the size based on the equilibrium rather than kinetics, producing CsPbX quantum dots nearly free of heterogeneous broadening in their exciton luminescence.