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.

Recent success in Mn2+ ion doping in cesium lead halide (CsPbX3) nanocrystals opened the door to exploring new optical, magnetic and charge carrier transport properties mediated via exciton–dopant exchange coupling in this new family of semiconductor nanocrystals. Here, we studied the dynamics of energy transfer from exciton to Mn2+ ions in Mn-doped CsPbCl3 nanocrystals to gain an insight into the relative strength of exciton–Mn exchange coupling compared to more extensively studied Mn-doped II–VI quantum dots. The comparison of exciton–Mn energy transfer times in CsPbCl3 nanocrystals and CdS/ZnS core/shell quantum dots suggests that exciton–Mn exchange coupling in CsPbX3 is not far behind that of CdS/ZnS despite the lack of quantum confinement. With further progress in the synthesis of Mn-doped CsPbX3 nanocrystals, such as imposing quantum confinement and expanding the range of host chemical composition, one could fully benefit from many properties of CsPbX3 superior to those of other semiconductor nanocrystals for hosting magnetic dopants.

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.

Metal–organic frameworks (MOFs) based on Ti-oxo clusters (Ti-MOFs) represent a naturally self-assembled superlattice of TiO2 nanoparticles separated by designable organic linkers as antenna chromophores, epitomizing a promising platform for solar energy conversion. However, despite the vast, diverse, and well-developed Ti-cluster chemistry, only a scarce number of Ti-MOFs have been documented. The synthetic conditions of most Ti-based clusters are incompatible with those required for MOF crystallization, which has severely limited the development of Ti-MOFs. This challenge has been met herein by the discovery of the [Ti8Zr2O12(COO)16] cluster as a nearly ideal building unit for photoactive MOFs. A family of isoreticular photoactive MOFs were assembled, and their orbital alignments were fine-tuned by rational functionalization of organic linkers under computational guidance. These MOFs demonstrate high porosity, excellent chemical stability, tunable photoresponse, and good activity toward photocatalytic hydrogen evolution reactions. The discovery of the [Ti8Zr2O12(COO)16] cluster and the facile construction of photoactive MOFs from this cluster shall pave the way for the development of future Ti-MOF-based photocatalysts.

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.