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. The high level of size control and ensemble uniformity achieved here will open the door to harnessing the benefits of excitons in CsPbX quantum dots for photonic and energy-harvesting applications.

Cesium lead halide (CsPbX) perovskite nanocrystals (NCs) possess the unique capability of post-synthesis anion exchange providing facile tunability of the optical properties, which is usually achieved by mixing NCs with reactive anion precursors. In this work, we show that the controllable anion exchange can be achieved in a dihalomethane solution of CsPbX NC in the absence of any spontaneously reacting anion source using photoexcitation of CsPbX NCs as the triggering mechanism for the halide ion exchange. The reaction begins with the photoinduced electron transfer from CsPbX NCs to dihalomethane solvent molecules producing halide ions via reductive dissociation, which is followed by anion exchange. The reaction proceeds only in the presence of excitation light and the rate and extent of reaction can be controlled by varying the light intensity. Furthermore, the asymptotic extent of reaction under continuous excitation can be controlled by varying the wavelength of light that self-limits the reaction when light becomes off-resonance with the absorption of NCs. The light-controlled anion exchange demonstrated here can be utilized to pattern the post-synthesis chemical transformation of CsPbX NCs, not readily achievable using typical methods of anion exchange.

We report the direct hot-injection synthesis of Mn-doped cesium lead bromide (CsPbBr3) perovskite nanocrystals. In contrast to Mn-doped CsPbCl3 nanocrystals, where doping of Mn under typical hot-injection synthesis condition has been relatively straightforward, extending the same approach to CsPbBr3 has been very difficult. Here, we achieved the synthesis of Mn-doped CsPbBr3 nanocrystals via the formation of an intermediate structure (L2[Pb1–x Mn x ]­Br4, L = ligand) before the hot-injection of the Cs precursor, which contains the same Mn–Br coordination present in Mn-doped CsPbBr3 nanocrystals. A strong correlation was observed between the Mn luminescence intensities of L2[Pb1–x Mn x ]­Br4 and Mn-doped CsPbBr3 nanocrystals, suggesting the possible role of L2[Pb1–x Mn x ]­Br4 as the structural precursor to Mn-doped CsPbBr3 nanocrystals. The successful Mn doping in CsPbBr3 nanocrystal host, which has significantly better optical characteristics than CsPbCl3 nanocrystals, will expand the range of useful properties of Mn-doped cesium lead halide perovskite nanocrystals resulting from the coupling of exciton and Mn.

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We report the strong light-induced activation of forbidden exciton transition in CsPbBr 3 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 3 quantum dots creates a sufficiently large perturbation via a lattice-distorting polaron, which turns on the formally forbidden transition. Compared to the bulk or weakly confined CsPbBr 3 , the activation of the forbidden transition in strongly confined quantum dots is much more prominent due to the stronger influence of the polaron on exciton transitions in the confined space. This nonlinear optical property highlights the intimate coupling of the photoexcited charge carriers with the lattice in the CsPbBr 3 quantum dots, allowing access to the forbidden exciton transitions with light.

To produce an epoxy resin with high intrinsic self‐healing efficiency, furfurylglycidyl ether (FGE) was synthesized following a two‐step route. It carried one furan and one epoxide on each of its molecules. Having been cured using N,N′‐(4,4′‐diphenylmethane)bismaleimide and methylhexahydrophthalic anhydride, FGE was then polymerized with two types of intermonomer linkages. That is, thermally reversible Diels–Alder (DA) bonds from the reaction between furan and maleimide groups, and thermally irreversible bonds from the reaction between epoxide and anhydride groups. These two types of bonds provide the polymer with thermal remendability and load‐bearing capacity, respectively. Compared with N,N‐diglycidylfurfurylamine, which was previously developed by the authors and has a similar structure to FGE but with fewer furan rings, FGE can react with maleimide with lower activation energy and the DA bonds formed exhibit higher reversibility. Consequently, improved crack healability of the cured FGE characterized by nearly full recovery of fracture toughness was revealed using double cleavage drilled compression tests. Copyright © 2010 Society of Chemical Industry

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.

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 CsPbBr3 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 CsPbBr3 and CsPbI3 quantum dots in the strongly confined regime, showing the clear role of confinement in determining the bright–dark energy splitting (ΔEBD) and the dark exciton lifetime (τD). We observe the increase in both ΔEBD and τD with increasing quantum confinement in CsPbBr3 and CsPbI3 QDs, consistent with the earlier predictions on the size-dependence of ΔEBD and τD. Our results show that quantum confinement plays a crucial role in determining the accessibility to the dark exciton PL and its characteristics in metal halide perovskite nanocrystals.