Stability and Degradation in Lead Halide Perovskite Nanocrystals via Regulation of Lattice Strain.

It is still quite challenging to achieve high-performance and stable blue perovskite materials due to their instability and degradation. The lattice strain provides an important pathway to investigate the degradation process. In this article, the lattice strain in perovskite nanocrystals was regulated by the ratio of Cs+, EA+, and Rb+ cations with different sizes. Their electrical structure, formation energy, and ion migration activation energy were calculated with the density functional theory (DFT) method. The luminescence properties and stability of blue lead bromide perovskite nanocrystals were analyzed with spectra regulation from 516 to 472 nm. It was demonstrated that the lattice strain plays an important role in the luminescence performance and degradation process of perovskite materials. The study provides the positive correlation between lattice strain and degradation as well as luminescence properties in lead halide perovskite materials, which is of great importance in uncovering their degradation mechanism and developing stable and high-performance blue perovskite materials.

Stable and Efficient Red-Emitting Perovskite Cross-Shaped Nanoplates.

The stable cross-shaped CsPbI3 nanoplates (NPs) with red emission were achieved by chemical synthesis with the assistance of YCl3. Y3+ replacing Pb2+ results in the anisotropic growth of the CsPbI3 nanocrystal to form NPs. Four corners of the NPs dissolved, thus forming the cross-shaped NPs. The emission of NPs was shifted from near-infrared (690 nm) to red emission (640 nm) as the dopant amount of Y3+ increased. Y3+ widens the width of the bandgap, which is also proved by first-principles calculations. In addition, the Cl- passivated the surface defects of the NPs, suppressing the nonradiative recombination. The NPs showed remarkable high photoluminescence quantum yields (PLQY) of 96%. PLQY is even more than 60% when NPs have been stored in a glovebox for more than 90 days. The NPs with adjustable wavelength and enhanced stability have a huge application potential in the field of a high-definition display.

A Novel Balloon Catheter-based Dilation Intervention for Patients with Cricopharyngeus Achalasia After Stroke: A Randomized Study.

This study aimed to investigate the efficacy and safety of a novel balloon catheter in dilation intervention for patients with cricopharyngeus achalasia after stroke. Thirty-four patients with cricopharyngeus achalasia after stroke received routine swallowing rehabilitation training and were randomly assigned to an experimental group (Exp, n = 17) that received dilation therapy using the novel balloon catheter once daily for 5 days per week or a control group (Con, n = 17) that received dilation therapy with a 14-Fr ordinary urinary catheter once daily for 5 days per week. The intervention duration, Eating Assessment Tool (EAT)-10 scores, and Functional Oral Intake Scale (FOIS) scores were recorded at baseline and each day during intervention. The time for a patient's FOIS score to be ≥ 3 as well as the recovery time for oral intake of water, liquid food, mushy food, and solid food were recorded or estimated. Complications were also recorded during intervention. The intervention duration was shorter in the Exp group than in the Con group (p = 0.005). The Exp group patients improved faster than the Con group patients, with a shorter recovery time for oral intake of liquid food (p = 0.002), mushy food (p = 0.001), and solid food (p = 0.001). At the time of intervention termination, EAT-10 scores were lower in the Exp group than in the Con group (p = 0.005). The Exp group had a similar incidence of complications as the Con group but with better tolerability (p = 0.028). Compared with the urinary catheter, the novel balloon catheter for dilation in patients with cricopharyngeus achalasia after stroke may lead to a better and more rapid recovery.

Synergistic function of doping and ligand engineering to enhance the photostability and electroluminescence performance of CsPbBr3quantum dots.

The photostability issue of CsPbX3(X = Cl, Br, I) quantum dots (QDs) is one of the key origins for the degradation of their luminescence performance, which hinders their application in lighting and displays. Herein, we report a new method combining doping and ligand engineering, which effectively improves the photostability of CsPbBr3QDs and the performance of QD light-emitting diodes (QLEDs). In this method, ZnBr2is doped into CsPbBr3QDs to reduce surface anion defects; didodecyldimethyl ammonium bromide (DDAB) and tetraoctylammonium bromide (TOAB) hybrid ligands, which have strong adsorption with QDs, are employed to protect the surface and enhance the conductivity of QD layer in QLEDs. The photoluminescence (PL) and transmission electron microscopy measurements prove the effectively improved photostability of CsPbX3QDs. Moreover, reduced defects and improved conductivity by doping and hybrid ligands treatment also enable the improved electroluminescence performance of CsPbX3QDs. The maximum luminance and external quantum efficiency of the QLED with optimized CsPbX3QDs are 3518.9 cd m-2and 5.07%, which are 3.6 and 2.1 times than that of the control device, respectively. Combining doping and hybrid ligands makes perovskite QDs have an extremely promising prospect in future applications of high-definition displays, high-quality lighting, as well as solar cells.

Modifying the Crystal Field of CsPbCl3:Mn2+ Nanocrystals by Co-doping to Enhance Its Red Emission by a Hundredfold.

CsPbCl3:Mn2+ is a practical solution for obtaining red-orange light inorganic perovskite nanocrystals since CsPbI3 is unstable. Increasing the concentration of Mn2+ is an effective way to enhance the orange-red emission of CsPbCl3:Mn2+. However, the relationship between emission intensity of the Mn2+ dopant and the concentration of Mn2+ is very chaotic in different studies. As a transition metal ion, the electronic states of Mn2+ are very sensitive to the crystal field environment. Here, the crystal field of the CsPbCl3:Mn2+ nanocrystals was adjusted by co-doping other cations, and the concentration of Mn2+ remained unchanged. Additionally, the crystal field strength of different samples was calculated. Compared with the CsPbCl3:Mn2+ nanocrystals, the red-orange peak in the fluorescence spectrum of CsPbCl3:Mn2+, Er3+ nanocrystals was redshifted from 580 to 600 nm and enhanced by 100 times successfully. The same experiment was carried out on CsPbCl3:Mn2+ nanoplatelets at the same time to confirm the changed crystal field around Mn2+. The effect of co-doping cations on the luminescence properties of Mn2+ is similar to that in nanocubes, and the mechanism was analyzed in detail.

CsPbBr3@CsPbBr3-x Cl x Perovskite Core-Shell Heterojunction Nanowires via a Postsynthetic Method with HCl Gas.

CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (NCs) are promising materials due to their excellent optoelectronic properties. This work shows a successful anion exchange reaction in CsPbBr3 nanowire (NW) systems with HCl gas resulting in a blue-green light-emitting CsPbBr3@CsPbBr3-x Cl x core-shell heterojunction. By adjusting the reaction time and the reaction temperature, the structure and light emission of the NWs can be adjusted. The core-shell heterojunction NCs are stably luminescent in 24 h. The rational mechanism of anion exchange in perovskite NCs is also investigated. The work highlights the feasibility of NWs heterogeneously prepared under the HC1 gas atmosphere, which provides a new strategy for studying the two- and multicolor luminescent perovskite NCs.

Improving the Quality and Luminescence Performance of All-Inorganic Perovskite Nanomaterials for Light-Emitting Devices by Surface Engineering.

Lead halide perovskites and their applications in the optoelectronic field have garnered intensive interest over the years. Inorganic perovskites (IHP), though a novel class of material, are considered as one of the most promising optoelectronic materials. These materials are widely used in detectors, solar cells, and other devices, owing to their excellent charge-transport properties, high defect tolerance, composition- and size-dependent luminescence, narrow emission, and high photoluminescence quantum yield. In recent years, numerous encouraging achievements have been realized, especially in the research of CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) and surface engineering. Therefore, it is necessary to summarize the principles and effects of these surface engineering optimization methods. It is also important to scientifically guide the applications and promote the development of perovskites more efficiently. Herein, the principles of surface ligands are reviewed, and various surface treatment methods used in CsPbX3 NCs as well as quantum-dot light-emitting diodes are presented. Finally, a brief outlook on CsPbX3 NC surface engineering is offered, illustrating the present challenges and the direction in which future investigations are intended to obtain high-quality CsPbX3 NCs that can be utilized in more applications.

The luminescence properties of CsPbxM1-xBr3 perovskite nanocrystals transformed from Cs4PbBr6 mediated by various divalent bromide MBr2 salts.

A novel high concentration doping method based on the transformation from Cs4PbBr6 nanocrystals (NCs), which reacted with divalent metal bromide MBr2, to CsPbxM1-xBr3 NCs was developed. Two types of M2+ and Zn2+ which cannot emit light and Mn2+ and Eu2+ which can be used as the luminous centres, were chosen to trigger the transformation of Cs4PbBr6 NCs to CsPbxM1-xBr3 NCs. CsPbxZn1-xBr3 NCs maintained high photoluminescence quantum yields (PLQY) (>75%) and had good dispersion in hexane without obvious dissolution or agglomeration after two weeks. By adjusting the reaction temperature, the intrinsic band edge luminescence and the emission of Mn2+ ions CsPbxMn1-xBr3 NCs show different colours of light from green, green-yellow, pink, and orange-red to purple under an excitation of 365 nm. CsPbxEu1-xBr3 NCs were synthesized for the first time, and a weak luminescence around 618 nm from Eu3+ was detected in addition to the band edge luminescence of NCs. X-ray photoelectron spectroscopy (XPS) data showed that Zn2+, Mn2+ and Eu3+ (Eu2+) doping concentrations are up to 80%, 75% and 50%, respectively. We also analysed the doping mechanism and compared the new method with the traditional high temperature injection method. The lead-depleted perovskite NCs transformed from Cs4PbBr6 can provide a feasible pathway to reduce the lead toxicity of perovskite NCs and expand their applications.

Water-resistant, monodispersed and stably luminescent CsPbBr3/CsPb2Br5 core-shell-like structure lead halide perovskite nanocrystals.

Lead halide perovskite materials are thriving in optoelectronic applications due to their excellent properties, while their instability due to the fact that they are easily hydrolyzed is still a bottleneck for their potential application. In this work, water-resistant, monodispersed and stably luminescent cesium lead bromine perovskite nanocrystals coated with CsPb2Br5 were obtained using a modified non-stoichiometric solution-phase method. CsPb2Br5 2D layers were coated on the surface of CsPbBr3 nanocrystals and formed a core-shell-like structure in the synthetic processes. The stability of the luminescence of the CsPbBr3 nanocrystals in water and ethanol atmosphere was greatly enhanced by the photoluminescence-inactive CsPb2Br5 coating with a wide bandgap. The water-stable enhanced nanocrystals are suitable for long-term stable optoelectronic applications in the atmosphere.

Inhibitory effect of oxymatrine on serum hepatitis B virus DNA in HBV transgenic mice.

AIM: To study the inhibitory effect of oxymatrine on serum hepatitis B virus (HBV) DNA in HBV transgenic mice. METHODS: HBV transgenic mice model was established by microinjection, and identified by HBV DNA integration and replication. Transgenic mice with replicating HBV were divided into 3 groups, and injected with normal saline (group A, n=9), 50 mg/kg (group B, n=8) and 100 mg/kg (group C, n=9) oxymatrine intraperitoneally once a day for 30 d, respectively. Quantitation of serum HBV DNA in HBV transgenic mice was performed by competitive polymerase chain reaction (PCR) in combination with DNA hybridization quantitative detection technique before and after treatment. RESULTS: Compared with pre-treatment, the serum HBV DNA in group A (F=1.04, P=0.9612) and group B (F=1.13, P=0.8739) had no changes after treatment. However, in group C serum HBV DNA was significantly decreased (F=13.97, P=0.0012). The serum HBV DNA after treatment was lower in group C than in groups B and A (F=8.65, P=0.0068; F=12.35, P=0.0018; respectively). The serum HBV DNA after treatment was lower in group B than in group A, but there was no statistical significance (F=1.43, P=0.652). CONCLUSION: Oxymatrine has inhibitory effects on serum HBV DNA in HBV transgenic mice.