Precursor Chemistry of Lead Bromide Perovskite Nanocrystals

We investigate the early stages of cesium lead bromide perovskite formation through absorption spectroscopy of stopped-flow reactions, high-throughput mapping, and direct synthesis and titration of potential precursor species. Calorimetric and spectroscopic measurements of lead bromide complex titrations combined with theoretical calculations suggest that bromide complexes with higher coordination numbers than previously considered for nonpolar systems can better explain observed behaviors. Synthesis mapping of binary lead halides reveals multiple lead bromide species with absorption peaks higher than 300 nm, including a previously observed species with a peak at 313 nm and two species with peaks at 345 and 370 nm that also appear as reaction intermediates during the formation of lead bromide perovskites. Based on theoretical calculations of excitonic energies that match within 50 meV, we give a preliminary assignment of these species as two-dimensional magic-sized clusters with side lengths of 2, 3, and 4 unit cells. Kinetic measurements of the conversion of benzoyl bromide precursor are connected to stopped-flow measurements of product formation and demonstrate that the formation of complexes and magic-sized clusters (i.e., nucleation) is controlled by precursor decomposition, whereas the growth rate of 2D and 3D perovskites is significantly slower.

Using the Photoluminescence Color Change in Cesium Lead Iodide Nanoparticles to Monitor the Kinetics of an External Organohalide Chemical Reaction by Halide Exchange

In this work, we demonstrate a photoluminescence-based method to monitor the kinetics of an organohalide reaction by way of detecting released bromide ions at cesium lead halide nanoparticles. Small aliquots of the reaction are added to an assay with known concentrations of CsPbI3, and the resulting Br-to-I halide exchange (HE) results in rapid and sensitive wavelength blueshifts (Δλ) due to CsPbBrxI3-x intermediate concentrations, the wavelengths of which are proportional to concentrations. An assay response factor, C, relates Δλ to Br- concentration as a function of CsPbI3 concentration. The observed kinetics, as well as calculated rate constants, equilibrium, and activation energy of the solvolysis reaction tested correspond closely to synthetic literature values, validating the assay. Factors that influence the sensitivity and performance of the assay, such as CsPbI3 size, morphology, and concentration, are discussed.

Traffic light-type ratiometric fluorescence visual sensing of Cs+ in soybean oil based on dimension regulation of 2D perovskite nanosheets

Determination of cesium ion in soybean oil is of high importance since the increasing risk from releasing of main component of nuclear waste cesium 137. The complex composition and high viscosity of soybean oil make it necessary to convert it into water phase by nitration before detection, so developing a simple, accurate and sensitive method for on-site sensing of Cs⁺ in soybean oil is still a big challenge. In this work, we report a traffic light-type ratiometric fluorescence strategy for the visual sensing of Cs⁺ in soybean oil based on dimensional regulation of two dimensional (PEA)₂PbI₄ perovskite nanosheets (NSs). The PEA⁺ in (PEA)₂PbI₄ NSs exchanged with Cs⁺ and lead to dimension of partial (PEA)₂PbI₄ NSs progressively increase from 2D to 3D CsPbI₃ NCs. Resultantly, the fluorescence of (PEA)₂PbI₄ NSs decreases with a concomitant fluorescence enhancement of CsPbI₃ NCs upon increasing the concentrations of Cs⁺, and the emission accordingly change from green, yellow to red with a high fluorescence colorimetric resolution up to 5.0 μM, make it successful to achieve on-site sensing of Cs⁺ in soybean oil just with naked eye in 5 min without any nitration, demonstrating a bright application future for determination of Cs⁺ in the soybean oil.

Recent progress and future prospects on halide perovskite nanocrystals for optoelectronics and beyond

As an emerging new class of semiconductor nanomaterials, halide perovskite (ABX3, X = Cl, Br, or I) nanocrystals (NCs) are attracting increasing attention owing to their great potential in optoelectronics and beyond. This field has experienced rapid breakthroughs over the past few years. In this comprehensive review, halide perovskite NCs that are either freestanding or embedded in a matrix (e.g., perovskites, metal-organic frameworks, glass) will be discussed. We will summarize recent progress on the synthesis and post-synthesis methods of halide perovskite NCs. Characterizations of halide perovskite NCs by using a variety of techniques will be present. Tremendous efforts to tailor the optical and electronic properties of halide perovskite NCs in terms of manipulating their size, surface, and component will be highlighted. Physical insights gained on the unique optical and charge-carrier transport properties will be provided. Importantly, the growing potential of halide perovskite NCs for advancing optoelectronic applications and beyond including light-emitting devices (LEDs), solar cells, scintillators and X-ray imaging, lasers, thin-film transistors (TFTs), artificial synapses, and light communication will be extensively discussed, along with prospecting their development in the future.

Recent Progress of Perovskite Nanocrystals in Chem/Bio Sensing

Perovskite nanocrystals (PNCs) are endowed with extraordinary photophysical properties such as wide absorption spectra, high quantum yield, and narrow emission bands. However, the inherent shortcomings, especially the instability in polar solvents and water incompatibility, have hindered their application as probes in chem/bio sensing. In this review, we give a fundamental understanding of the challenges when using PNCs for chem/bio sensing and summarize recent progress in this area, including the application of PNCs in various sensors and the corresponding strategies to maintain their structural integrity. Finally, we provide perspectives to promote the future development of PNCs for chem/bio sensing applications.

Bromopropane as a novel bromine precursor for the completely amine free colloidal synthesis of ultrastable and highly luminescent green-emitting cesium lead bromide (CsPbBr3) perovskite nanocrystals

Recently, lead halide perovskite nanocrystals (PNCs) have attracted intense interest as promising active materials for optoelectronic devices. However, their extensive applications are still hampered by poor stability under ambient conditions. Oleic acid and oleylamine are the most commonly used ligands in colloidal CsPbX₃ (X = Cl, Br, and I) synthesis. Oleylamine plays a dual role as it stabilizes the surface but in the long run or post-synthesis, it may disturb the colloidal stability due to facile proton exchange leading to the formation of labile oleylammonium halide, which detaches the halide ions from the NC surface. To address these issues, herein, we report an open-atmospheric, facile, efficient, and completely amine-free synthesis of cesium lead bromide perovskite nanocrystals using a novel bromine precursor, bromopropane, which is inexpensive and available at hand. The reaction mechanism follows a trioctylphosphine/oleic acid-mediated surface passivation route that provides an amine-free reaction environment to stabilize ligand capping on the NC surface. Uniform, highly monodisperse NCs of size ∼29 nm were obtained. The as-synthesized NCs have a high photoluminescence quantum yield (PLQY) of around 80%, and especially, exhibited strong stability under ambient conditions and continuous UV irradiation. The PLQY can maintain 83% of the initial one even after 120 days. Furthermore, after 96 h of continuous irradiation under UV light at 365 nm (8 W cm^-2) under open ambient conditions, the photoluminescence (PL) intensity showed retention of 68% of its original value with no significant changes in the full width at half-maximum, whereas the amine-based sample retains only 5% of its original PL intensity. Furthermore, we have utilized these NCs to fabricate stable down-converted LED devices. The present work demonstrated the synthesis of ultra-stable CsPbBr₃ NCs that can be an ideal candidate for display applications.

Colorimetric sensing of chloride in sweat based on fluorescence wavelength shift via halide exchange of CsPbBr3 perovskite nanocrystals

Considering the high importance of the rapid detection of chloride ion (Cl^-) in sweat for the diagnosis of fibrotic cysts, we have investigated the heterogeneous halide exchange between CsPbBr₃ perovskite nanocrystals (PNCs) in n-hexane and Cl^- in aqueous solution. The results show that CsPbBr₃ PNCs could achieve fast halide exchange with Cl^- in the aqueous phase under magnetic stirring at pH = 1, accompanied by a significant wavelength blue shift and vivid fluorescence color changes from green to blue. Therefore, a fluorescence wavelength shift-based colorimetric sensing of Cl^- based on the halide exchange of CsPbBr₃ PNCs has been developed to realize the rapid detection of Cl^- in sweat. Compared with the conventional fluorescence intensity-based method, this method is of high convenience since the whole procedure could be achieved within 5 min without any sample pretreatment (even no dilution), demonstrating promising application prospects. Graphical Abstract Fluorescence wavelength-shift based colorimetric sensing of chloride in sweat via halide exchange of CsPbBr₃ perovskite nanocrystals.