Perovskite and chalcogenide quantum dots (QDs) are important nano semiconductors. It has been a challenge to synthesize heterostructural QDs combining perovskite and chalcogenide with tailorable photoelectronic properties. In this report, heterostructural CsPbX3-PbS (X = Cl, Br, I) QDs were successfully synthesized via a room temperature in situ transformation route. The CsPbX3-PbS QDs show a tunable dual emission feature with the visible and near-infrared (NIR) photoluminescence (PL) corresponding to CsPbX3 and PbS, respectively. Typically, the formation and evolution of the heterostructural CsPbBr3–PbS QDs with reaction time was investigated. Femtosecond transient absorption spectroscopy (TAS) was applied to illuminate the exciton dynamics in CsPbBr3–PbS QDs. The mild synthetic method and TAS proved perovskite to PbS energy transfer may pave the way toward highly efficient QD photovoltaic and optoelectronic devices.
Low dimensional semiconductor nanomaterials have shown their tailorable properties for a variety of promising applications in decades. Here a general strategy to synthesize all-inorganic CsPbX 3 (X = Cl, Br, I or their mixture) perovskite 2D nanoplates by introducing additional metal halides MX' 2 or MX' 3 (M = Cu, Zn, Al or Pb, etc.; X' = Cl, Br or I) is reported. These CsPbX 3 perovskite nanoplates have uniform thickness and tunable size, which can be feasibly controlled by the component and ratio of the metal halides, temperature, time, and ligands. The well-defined morphology of the nanoplates makes them ideal building blocks for the self-assembly in the face-to-face and column-by-column arrangement. Compared to the optically isotropic CsPbX 3 nanocubes, the 2D CsPbX 3 nanoplates exhibit remarkable polarized UV-vis absorption and photoluminescence not only in liquid solvent and solid resin matrix, but also in self-assembled films. An optoelectronic photodetector sensitive for linear polarized light is fabricated to demonstrate the proof-of-concept.
Purpose: Sparse-data computed tomography (CT) frequently occurs, such as breast tomosynthesis, Carm CT, on-board four-dimensional cone-beam CT (4D CBCT), and industrial CT. However, sparse-data image reconstruction remains challenging due to highly undersampled data. This work develops a datadriven image reconstruction method for sparse-data CT using deep neural networks (DNN). Methods: The new method so-called AirNet is designed to incorporate the benefits from analytical reconstruction method (AR), iterative reconstruction method (IR), and DNN. It is built upon fused analytical and iterative reconstruction (AIR) that synergizes AR and IR via the optimization framework of modified proximal forward-backward splitting (PFBS). By unrolling PFBS into IR updates of CT data fidelity and DNN regularization with residual learning, AirNet utilizes AR such as FBP during the data fidelity, introduces dense connectivity into DNN regularization, and learns PFBS coefficients and DNN parameters that minimize the loss function during the training stage; and then AirNet with trained parameters can be used for end-to-end image reconstruction. Results: A CT atlas of 100 prostate scans was used to validate the AirNet in comparison with stateof-art DNN-based postprocessing and image reconstruction methods. The validation loss in AirNet had the fastest decreasing rate, owing to inherited fast convergence from AIR. AirNet was robust to noise in projection data and content differences between the training set and the images to be reconstructed. The impact of image quality on radiotherapy treatment planning was evaluated for both photon and proton therapy, and AirNet achieved the best treatment plan quality, especially for proton therapy. For example, with limited-angle data, the maximal target dose for AirNet was 109.5% in comparison with the ground truth 109.1%, while it was significantly elevated to 115.1% and 128.1% for FBPConvNet and LEARN, respectively.
CsPbX 3 (X = Cl, Br, I) perovskite nanowires and nanorods are important 1D and quasi 1D semiconductor nanomaterials. They have shown significant prospect in optic and optoelectronic applications, especially for their adaptability to flexible devices, good carrier transport performance, polarized absorption, and emission properties. Due to the high dependence of the property to the morphology, it is crucial to develop synthesis methods with continuous diameter and length tunability of the 1D/quasi 1D perovskites. In this report, a feasibly room temperature synthesis method was developed for ultrathin CsPbX 3 (X = Cl, Br, I) perovskite nanowires. By aging the CsPbBr 3 nanowires (≈2*500 nm) under ambient condition with proper concentration and time, the nanowires are transformed to nanorods with controllable diameter and length. Reversibly, the nanorods can be transformed back to nanowires. Equilibrium mechanism is adopted to understand the morphology evolution, and hopefully could be generally applied to many other nano materials. The polarized optoelectronic properties of the nanowires and nanorods are interpreted by a model based on the two-channel anisotropies measurement. Polarized light detectors constructed by oriented assembled nanowires are fabricated to demonstrate their application potentials.
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