Organic Amine-Bridged Quasi-2D Perovskite/PbS Colloidal Quantum Dots Composites for High-Gain Near-Infrared Photodetectors.

Near-infrared (NIR) II detection at weak flux intensity is required in medical imaging and is especially urgent in light of the low quantum efficiency of NIR-II dyes. The low responsivity of traditional photodetectors in this region limits image quality. Here, we report a NIR-II photodetector with high gain based on perovskite coupled PbS colloidal quantum dots (CQDs). Tailoring the trap density of CQDs by designing surface ligands with dual functionality contributed to control over trap-induced charge-injection upon light illumination. As a result, a detector with high gain is realized, showing external quantum efficiency of 1260% at 1200 nm and achieving the lowest detectable light intensity, that is, as low as 0.67 pW cm-2 with a linear dynamic range of 200 dB. Devices maintain over 90% of responsivity after 150 days of storage. We acquired images of a butterfly wing, showing the skeleton texture with a maximum spatial resolution of 3.9 lp/mm.

Low Bandgap 2D Perovskite Single Crystal with Anomalous-large Charges/ions Collection Ratio for Ultra-sensitive and Stable X-ray Detectors.

The low-dimensional halide perovskites have attracted increasing attention due to their improved moisture stability, reduced defects, and suppressed ions migration in many optoelectronic devices such as solar cells, light-emitting diodes, X-ray detectors, and so on. However, they are still limited by their large band gap and short charge carriers' diffusion length. Here, we demonstrate that the introduction of metal ions into organic interlayers of two-dimensional (2D) perovskite by cross-linking the copper paddle-wheel cluster-based lead bromide ([Cu(O2 C-(CH2 )3 -NH3 )2 ]PbBr4 ) perovskite single crystals with coordination bonds can not only significantly reduce the perovskite band gap to 0.96 eV to boost the X-ray induced charge carriers, but can also selectively improve the charge carriers' transport along the out-of-plane direction and blocking the ions motion paths. The [Cu(O2 C-(CH2 )3 -NH3 )2 ]PbBr4 single-crystal device can reach a record charges/ions collection ratio of 1.69×1018 ±4.7 % µGyair -1 s, and exhibit a large sensitivity of 1.14×105 ±7% µC Gyair -1 cm-2 with the lowest detectable dose rate of 56 nGyair s-1 under 120 keV X-rays irradiation. In addition, [Cu(O2 C-(CH2 )3 -NH3 )2 ]PbBr4 single-crystal detector exposed to the air without any encapsulation shows excellent X-ray imaging capability with long-term operational stability without any attenuation of 120 days.

Porous Nanosheet Assembly for Macrocyclization and Self-Release.

Macrocyclic structures are challenging synthetic targets owing to various potential applications ranging from drug discovery to nanomaterials. Their use, however, is highly limited due to synthetic difficulties arising from an entropic penalty for folding of linear chains. Here, we report single-layered porous nanosheets with 2D ordered internal cavities that act as a highly efficient macrocycle generator, changing linear substrates to release as macrocycles in aqueous methanol solution. The nanosheets with hydrophobic cavities encapsulate a linear substrate with nearly perfect uptake, perform clean cyclization, and then spontaneously release as a pure macrocycle. The self-separation of the macrocycle that precipitates from the solution leads to repeated cycles of macrocycle generation; thereby, the single-layered porous materials enabling catch and release offer a powerful novel strategy for repeated macrocycle generation.

[Design and application of artificial multicellular systems for nitrogen removal from wastewater].

Excessive accumulation of nitrogen is a major cause of water eutrophication. Developing an inexpensive and efficient nitrogen removal technology is therefore essential for wastewater purification. The microbial technology for nitrogen removal has been widely used for its low cost, high efficiency, and strong environmental adaptability. Most recently, with the advances in synthetic biotechnology, artificial multicellular systems have been sufficiently developed and exhibited unique definability and controllability. Compared with those in the natural microbial consortia, the nitrogen removal pathways and environmental response mechanisms are easy to be clarified in the artificial multicellular systems, which allow for efficient nitrogen removal under low cellular metabolic loading. Therefore, artificial multicellular systems demonstrate great application potential in the purification of wastewater, including landfill leachate, industrial wastewater, seawater aquaculture wastewater, and domestic sewage. We focused on the design, building, and application of artificial multicellular systems for nitrogen removal from wastewater. Specifically, we summarized the functional microorganisms and their nitrogen removal mechanisms, introduced the design principles and building methods of artificial multicellular systems, illustrated the application of artificial multicellular systems with examples, and prospected the future research trend in nitrogen removal from wastewater. The conclusion is expected to provide new insights and efficient strategies for optimizing the microbial nitrogen removal from wastewater.

Arising 2D Perovskites for Ionizing Radiation Detection.

2D perovskites have greatly improved moisture stability owing to the large organic cations embedded in the inorganic octahedral structure, which also suppresses the ions migration and reduces the dark current. The suppression of ions migration by 2D perovskites effectively suppresses excessive device noise and baseline drift and shows excellent potential in the direct X-ray detection field. In addition, 2D perovskites have gradually emerged with many unique properties, such as anisotropy, tunable bandgap, high photoluminescence quantum yield, and wide range exciton binding energy, which continuously promote the development of 2D perovskites in ionizing radiation detection. This review aims to systematically summarize the advances and progress of 2D halide perovskite semiconductor and scintillator ionizing radiation detectors, including reported alpha (α) particle, beta (ß) particle, neutron, X-ray, and gamma (γ) ray detection. The unique structural features of 2D perovskites and their advantages in X-ray detection are discussed. Development directions are also proposed to overcome the limitations of 2D halide perovskite radiation detectors.

Robust Organogel Scintillator for Self-healing and Ultra-flexible X-ray Imaging.

Metal halide scintillators serve as promising candidates for X-ray detection due to their high attenuation coefficients, high light yields, and low-cost solution-processable characteristics. However, the issues of humidity/thermal quenching and mechanical fragility, remain obstacles to the broad and diversified development of metal halide scintillators. Here, this work reports a lead-free, water-stable, stretchable, and self-healing (ethylenebis-triphenylphosphonium manganese (II) bromide (C38H34P2)MnBr4 organogel scintillator that meets X-ray imaging in complex scenarios. The robust organogel scintillator can be stretched with elongation up to 1300% while maintaining the scintillation properties. Activated by the dynamic hydrogen bonds and coordination bonds design, the organogel scintillator exhibits excellent self-healing properties at room temperature to alleviate the vignetting problem of the rigid scintillator films, the X-ray imaging resolution can reach 16.7 lp mm-1. The organogel scintillator can also realize flexible and self-healing X-ray imaging in water, providing a design path for portable devices in harsh conditions.

Cation-π interactions enabled water-stable perovskite X-ray flat mini-panel imager.

Sensitive and stable perovskite X-ray detectors are attractive in low-dosage medical examinations. The high sensitivity, tunable chemical compositions, electronic dimensions, and low-cost raw materials make perovskites promising next-generation semiconductors. However, their ionic nature brings serious concerns about their chemical and water stability, limiting their applications in well-established technologies like crystal polishing, micro-processing, photolithography, etc. Herein we report a one-dimensional tryptamine lead iodide perovskite, which is stable in water for several months as the strong cation-π interactions between organic cations. The one-dimensional and two-dimensional tryptamine lead iodide perovskite tablets are switchable through thermal-annealing or water-soaking treatments to relax microstrains. The water-stable and microstrain-free one-dimensional perovskite tablets yield a large sensitivity of 2.5 × 106 µC Gyair-1 cm-2 with the lowest detectable dose rate of 5 nGyair s-1. Microelectrode arrays are realized by surface photolithography to construct high-performance X-ray flat mini-panels with good X-ray imaging capability, and a record spatial resolution of 17.2 lp mm-1 is demonstrated.

Prominent Free Charges Tunneling Through Organic Interlayer of 2D Perovskites.

The diversity of organic cations greatly enriches the species of 2D perovskites; traditional 2D Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) perovskites are synthesized by two different organic amines. Here, according to the difference in pKa values between conjugated acids of monoprotonated and biprotonated 4-(2-Aminoethyl)pyridine (4AEPy) ions, the 2D perovskites of RP (4AEPy)2 PbI4 and DJ (4AEPy)PbI4 from same organic amine is reported, which can realize reversible transformation under the treatment of HI and NH3 , respectively. The interaction of N-H···N hydrogen bond between adjacent organic molecules in (4AEPy)2 PbI4 leads to the bending conformation of ethylamine groups, which results in a 2.4 Å reduction in layer spacing compared to typical phenylethylamine lead iodine ((PEA)2 PbI4 ) 2D perovskite. Besides, the ethylamine groups of organic layers in (4AEPy)PbI4 are deeply inserted into octahedral cavities and directly participate in the construction of the conduction band minimum, which leads to a small exciton binding energy of 27.3 meV to generate free charges. The stronger coupling between the organic and inorganic layers and the minor exciton binding energy can promote the DJ phase to possess a more stable structure and better optoelectronic properties. Thus the (4AEPy)PbI4 device displays better light response and X-ray detection capability with a high sensitivity of 5627 µC Gyair -1 cm-2 and the lowest detectable dose rate of 20 nGyair s-1 .

Spray-coated perovskite hemispherical photodetector featuring narrow-band and wide-angle imaging.

Sphere imagers featuring specific wavelength recognition and wide-angle imaging are required to meet the fast development of modern technology. However, it is still challenging to deposit high-quality photosensitive layers on sphere substrates from low-cost solution processes. Here we report spray-coated quasi-two-dimensional phenylethylammonium/formamidinium lead halide (PEA2FAn-1PbnX3n+1) perovskite hemispherical photodetectors. The crystallization speed is manipulated by perovskite compositions, and the film thickness can be controlled by spray-coating cycles and solution concentration from tens of nanometers to hundreds of micrometers with a fast velocity of 1.28 × 10-4 cm3 s-1. The lens-free hemispherical photodetectors allow light response at a wide incident angle of 180°. Simultaneously, the wavelength selective response from visible to the near-infrared range is achieved with full width at half maximums (FWHMs) of ~20 nm, comparable to single-crystal devices. Wide-angle and wavelength-selective imaging are also demonstrated, which can find potential applications in intelligent recognition and intraoperative navigated surgery.

Carbonized polymer dots enhanced stability and flexibility of quasi-2D perovskite photodetector.

Quasi-2D perovskites have been demonstrated to be competitive materials in the photodetection fields due to the enhanced moisture stability by large organic cations. However, as the increasing demands of modern technology, it is still challenging to combine the flexibility with the capability of weak light detection in a low-cost way. Here, amides, carboxylic acids, and anhydrides groups-rich carbonized polymer dots (CPDs) were employed to fill in the perovskite grain boundaries, which can passivate the point defects of perovskite by coordinating with the unbonded Pb atoms, and reduce the leakage current. Weak light detection capability was demonstrated by directly resolving light with an intensity of 10.1 pW cm-2. More importantly, the stretchable polymer chains on CPDs strongly interact with perovskite ions through multiple supramolecular interactions, and extend the stretchable properties to the perovskite/CPDs composites, which can maintain the integral structure stability during the deformation of perovskite crystals and restricted any crack by releasing the film strain. Our fabricated devices show extraordinary flexible stability in the bending-dependent response tests. The viscoelasticity of CPDs improves the bending stability of the flexible quasi-2D perovskite photodetectors, and device performance shows no degradation after bending 10000 times, comparable or even outperforming the dominating flexible photodetectors.

Photo-excitation production of medically interesting isomers using intense γ-ray source.

Photon-induced nuclear excitation (i.e. photo-excitation) can be used for production of nuclear isomers, which have potential applications in astrophysics, energy storage, medical diagnosis and treatment. This paper presents a feasibility study on photo-excitation production of four nuclear isomers (103mRh, 113m,115mIn and 176mLu) with intense γ-ray source based on laser-electron Compton scattering (LCS). The decay properties of these isomers and their potential applications in medical diagnosis and treatment were reviewed. The cross-section curve, simulated yield and activity of product of each photo-excitation process were calculated. The cutoff energy of LCS γ-ray beam was optimized by adjusting electron beam energy in order to maximize the isomer activity. It is found that the specific activity of the above-mentioned isomers can exceed ~0.2 GBq/g for 6-h target irradiation at an intensity of 1013 γ/s. Our simulation results suggest the prospect of producing medically interesting radionuclides with photo-excitation using the state-of-art LCS γ-ray beam facility.

Development of Halide Perovskite Single Crystal for Radiation Detection Applications.

Preface: Recently, low-cost perovskite single crystals have attracted intensive attention due to their excellent optoelectronic properties and improved stability when compared to polycrystalline films for various applications, such as solar cells (Kojima et al., 2009; Lee et al., 2012; Tsai et al., 2016; Sahli et al., 2018), lasers (Gu et al., 2016; Veldhuis et al., 2016), radiation detection (Kim et al., 2017), and so on. The unique optoelectronic properties and low-cost growing processes for large-sized single crystals also make them greatly suitable for radiation detection. In this review, we summarize various synthesis methods of perovskite single crystals and introduced the high radiation detection performance of the perovskite single crystal. The advantages and limitations of halide perovskite single crystals as radiation detector candidates will be discussed in detail, and corresponding future development trends can be expected by overcoming current obstacles (Leijtens et al., 2018; Boyd et al., 2019), such as ion migration (Eames et al., 2015), stability, etc.

Sensitive and Stable 2D Perovskite Single-Crystal X-ray Detectors Enabled by a Supramolecular Anchor.

Perovskite X-ray detectors have been demonstrated to be sensitive to soft X-rays (<80 keV) for potential medical imaging applications. However, developing X-ray detectors that are stable and sensitive to hard X-rays (80 to 120 keV) for practical medical imaging is highly desired. Here, a sensitive 2D fluorophenethylammonium lead iodide ((F-PEA)2 PbI4 ) perovskite single-crystal hard-X-ray detector from low-cost solution processes is reported. Dipole interaction of organic ions promotes the ordering of benzene rings as well as the supramolecular electrostatic interaction between electron-deficient F atoms with neighbor benzene rings. Supramolecular interactions serve as a supramolecular anchor to stabilize and tune the electronic properties of single crystals. The 2D (F-PEA)2 PbI4 perovskite single crystal exhibits an intrinsic property with record bulk resistivity of 1.36 × 1012 Ω cm, which brings a low device noise for hard X-ray detection. Meanwhile, the ion-migration phenomenon is effectively suppressed, even under the large applied bias of 200 V, by blocking the ion migration paths after anchoring. Consequently, the (F-PEA)2 PbI4 single crystal detector yields a sensitivity of 3402 µC Gy-1 air cm-2 to 120 keVp hard X-rays with lowest detectable X-ray dose rate of 23 nGyair s-1 , outperforming the dominating CsI scintillator of commercial digital radiography systems by acquiring clear X-ray images under much lower dose rate. In addition, the detector shows high operation stability under extremely high-flux X-ray irradiation.