Nano Research最新文献

Lead sulfide quantum dots (PbS QDs) are promising candidates for high-performance solar cells due to their tunable bandgaps and low-cost solution processing. However, low carrier mobility and numerous surface defects restrict the performance of the fabricated solar cells. Herein, we report the synthesis of novel PbS-perovskite core-shell QDs to solve the low carrier mobility problem of PbS QDs via a facile hot injection method. CsPbI₂Br shell enabled strain-free epitaxial growth on the surface of PbS QDs because of 98% lattice match. Our results demonstrate a significant improvement in the photoluminescence and stability of the synthesized PbS-CsPbI₂Br QDs upon shell formation, attributed to the effective suppression of surface defects by the epitaxial shell of CsPbI₂Br. As a result, the obtained solar cell based on PbS-CsPbI₂Br core-shell QD exhibits a power conversion efficiency (PCE) of 8.43%, two times higher than that of pristine PbS QDs. Overall, the construction of PbS-CsPbI₂Br core-shell structures represent a promising strategy for advancing the performance of PbS QDs-based optoelectronic devices.

Understanding the mechanisms of degradation in lead halide perovskite nanocrystals is critical for their future application in optoelectronic devices. We report single-particle measurements of the photoluminescence from cesium lead bromide nanocrystals coated with a silica shell (CsPbBr₃@SiO₂). Through correlative imaging, we quantified changes in the fluorescence intensity trajectories of the same nanocrystals before and after annealing them at different temperatures. We observe that nearly equal numbers of CsPbBr₃@SiO₂ nanocrystals exhibit an increase versus decrease in the amount of time they spend in an emissive state after annealing at temperatures of 70 and 100 °C. On the other hand, annealing at 120 °C produces a decrease in the on-fraction for most nanocrystals and, correspondingly, a substantial decrease in the photoluminescence intensity for a thin film annealed at this temperature. We attribute the differences in behavior among individual nanocrystals to heterogeneity in the distribution of trap states that are initially present. X-ray photoelectron, time-resolved photoluminescence, and transient absorption spectroscopies performed on thin films of CsPbBr₃@SiO₂ nanocrystals indicate that thermal annealing heals electron traps by passivating surface Pb ions and simultaneously creates hole traps through the formation of Pb and Cs vacancies. The relative rates of these parallel processes depend on the annealing temperature, which are important to account for when developing passivation strategies for lead halide perovskite nanocrystals in optoelectronic devices that will operate at elevated temperatures.

Spermine assumes a pivotal role in assessing food safety due to its potential to induce a spectrum of diseases upon excessive consumption. However, contemporary spermine detection methodologies, exemplified by high-performance liquid chromatography (HPLC), demand costly instrumentation and the expertise of skilled technicians. To address this challenge, the study introduces a portable fluorescence sensing platform. Ratiometric fluorescent probes were realized through the utilization of CdS quantum dots deeply doped with Ag⁺ (CdS:Ag QDs) and nitrogen-doped carbon quantum dots (N-CQDs). Hydrogen bonds formed between CdS:Ag QDs and spermine result in the formation of the assembly and the decreasing of the fluorescence intensity. In an effort to broaden the applicative scope and streamline deployment processes, fluorescent sensing hydrogels were meticulously engineered, capitalizing on the swelling properties inherent in polyvinyl alcohol (PVA) hydrogels. The systematic delineation of the correlation between 1 − R/B and spermine concentration facilitates the quantitative determination of spermine concentration. The incorporation of this composite construct serves to alleviate environmental influences on the probes, thereby augmenting their precision. The portable fluorescent sensing platform proves pivotal in expeditiously measuring spermine concentration within the fluorescent sensing hydrogel, enabling a quantitative assessment of pork freshness. The utilization of this platform for food freshness evaluation imparts the benefits of convenience, cost-effectiveness, and intuitive operation.

Plasmonic nanostructures stand at the forefront of nanophotonics research, particularly in sensing and energy conversion applications. Their unique ability to confine light energy at the nanoscale makes them indispensable for a wide array of technological advancements. The study of these structures often makes use of different materials and, even more extensively, explores new shapes and configurations to extend our common repertoire of useful nanophotonics tools. Exploring the creation of bimetallic plasmonic nanostructures combines these two dimensions determining the space of possible plasmonic resonators and opens the possibility of tailoring systems with behavior unavailable to single-metal plasmonic structures. In this paper, we delve into the exploration of bimetallic systems employing plasmonic nanostars. These structures have demonstrated remarkable capabilities for surface-enhanced Raman scattering (SERS) spectroscopy and photochemistry, due to the strong plasmonic response of their peaks, whose disposition following a spherical symmetry makes them largely polarization- and orientation-insensitive. Herein, we report the colloidal synthesis of two different water-stable Au@Ag nanostars, explore their performance as photocatalysts and SERS substrates, and provide an in-depth account of their non-trivial physical response.

The impact of alkali metal carboxylates on the synthesis of colloidal quantum dots (CQDs) was investigated. Through a ligand removal experiment, we demonstrated that due to its high hydrophilic nature, sodium oleate dispersed in n-octadecene (ODE) with the formation of micelles with the help of other polar molecules, which resulted in reduced concentration of oleic acid and cadmium oleate both in the solution and on the surface of CQDs. These effects allow for control the size of CdSe CQDs in a wide range when synthesizing them by solely changing the amount of sodium oleate, under either cation-rich or anion-rich conditions. Additionally, enhanced ligand dynamics promote morphology transformation and suppress size deviation caused by different morphologies’ existence in CQDs synthesis. Alkali metal oleate not only stabilized anion-rich CdSe CQDs but also results in highly crystallized wurtzite structure of CdSe CQDs when synthesizing them with excess anions. Furthermore, under anion-rich synthetic condition, anisotropic growth can be realized, leading to nanorods and nanoplatelets based on the alkali metal ions used. Given their outstanding effects and widely applicable synthetic conditions, alkali metal carboxylates offer new possibilities for designing efficient methods for synthesizing CQDs.

Low-dimensional materials, with highly tunable electronic structures depending on their sizes and shapes, can be exploited as fundamental building blocks to construct higher-order structures with tailored emergent properties. This is akin to molecules or crystals that are assembled by atoms with diverse symmetries and interactions. Prominent low-dimensional materials developed in recent decades include zero-dimensional (0D) quantum dots, one-dimensional (1D) carbon nanotubes, and two-dimensional (2D) van der Waals materials. These materials enclose a vast diversity of electronic structures ranging from metals and semimetals to semiconductors and insulators. Moreover, low-dimensional materials can be assembled into higher-order architectures known as superlattices, wherein collective electronic and optical behaviors emerge that are absent in the individual building blocks alone. Superlattices composed of interacting low-dimensional entities thus define an ultra-manipulatable materials platform for realizing artificial structures with customizable functionalities. Here, we review significant milestones and recent progress in the field of low-dimensional materials and their superlattices. We survey recently observed exotic emergent electronic and optical properties in these materials and delve into the underlying mechanisms driving these phenomena. Additionally, we hint the future opportunities and remaining challenges in advancing this exciting area of research.

This review focuses on the history and current state of the art optoelectronic applications of quantum dots involving light emission. We focus mainly on three areas of commercial, or potential commercial interest, including quantum dot light emitting devices (QLEDs, sometimes called QD-LEDs), lasing applications, and quantum computing applications. The main connection between these areas is the development of the science and engineering needed to achieve electrical excitation of the quantum dot in an optoelectronic device in order to achieve emission with characteristics particularly suited to the application in question. Due to the special physics of quantum dots, these materials are particularly well suited for both existing commercial applications, and potentially for future applications, such as single photon sources, spin cubits, or polarized emission. We conclude with an analysis of the future prospects for these exciting materials. Given 30 years of progress since the Nobel Prize winning work on monodisperse samples of QDs, our goal is to highlight the current start of the art, discuss the current issues for each technology, and suggest future goals for the next 30 years for quantum dot research.

Silver-based quantum dots (QDs) such as Ag₂S, Ag₂Se, and Ag₂Te, which emit in the second near-infrared window (NIR-II, 900–1700 nm), have attracted great research interest due to their prominent optical properties and eco-friendly compositions. Over the past decade, the controllable synthesis, bandgap modulation, and fluorescence improvement of NIR-II Ag-based QDs have greatly promoted their practical applications. In this review, we summarize the development process and latest achievements of NIR-II Ag-based QDs, covering major synthesis techniques for fabricating NIR-II Ag-based QDs, general methods for improving their fluorescence properties and recent advances in the applications of NIR-II Ag-based QDs from bioimaging to optoelectronic devices. Finally, we discuss the challenges and prospects of NIR-II Ag-based QDs in their optical properties and applications. This review aims to present synthesis and modification strategies and future application prospects for NIR-II Ag-based QDs, providing guidance for the design and integration of fluorescent probes in NIR-II window.

The instability of colloidal lead halide perovskite nanocrystals (NCs) presents a significant challenge for their application in optoelectronic devices. This review examines the primary causes of instability in these NCs and the proposed mechanisms of degradation. It also introduces the recently developed synthesis and surface passivation methods to address the instability issue of colloidal perovskite NCs. Specifically, we focus on the various types of ligands and precursors introduced during NC synthesis or post-treatment and how they impact the structural and optical properties of the perovskite NCs. This review also proposes a systematic approach to evaluating stability enhancement strategies by establishing key parameters and ranking them based on working and processing conditions. Finally, we discuss the issues that need to be addressed in future research to achieve practical application of lead halide perovskite NCs in advanced optoelectronic systems.

In colloidal quantum dots (QDs), the geometries of surface ligands may play significant roles in tuning the electronic structure, optical spectra and exciton dynamics. We here propose an effective approach to build a diverse dataset of small QDs, based on which the machine learning force field (MLFF) can be obtained based on the DeePMD framework and the energy of each atom is expressed based on the local atomic structure. Using the obtained QD force field (QDFF), molecular dynamics simulation of large zinc-blende CdSe QDs passivated by carboxylate ligands is successfully carried out, and the complex surface structure is extensively studied. We find that bridging, tilted, chelating and claw geometries are the major geometries of carboxylate ligands in CdSe QDs, and the alkyl chain length of ligands plays a significant role. The Markov state model is utilized to reveal the detailed geometry transformation channels. Due to the high performance of QDFF, the present approach is promising for systematic studies of large QDs with different kinds of ligands that can be synthesized in experiment.