Search

The synthesis of N-unprotected isoindolinones via rhodium(III)-catalyzed intramolecular C(sp3)–H amidation of various 2-methyl-N-substituted benzamides is developed. This protocol employs a free amino acid l-alanine as a ligand, which could significantly increase the reactivity of rhodium catalyst.

Lanthanide doped fluorescence nanoparticles have gained considerable attention in biomedical applications. However, the low uptake efficiency of nanoparticles by cells has limited their applications. In this work, we demonstrate how the uptake efficiency is affected by the size of nanoparticles under flow conditions. Using the same size NaYF4:20% Yb3+,2% Er3+,2% Ce3+ nanoparticles as core, NaYF4:20% Yb3+,2% Er3+,2% Ce3+@NaYF4 core-shell structured nanorods with different sizes of 60–220 nm were synthesized by thermal decomposition and hot injection method. Under excitation at 980 nm, a strong upconversion green emission (541 nm, 2H11/2 → 4I15/2 of Er3+) is observed for all samples. The emission intensity for each size nanorod was calibrated and is found to depend on the width of NRs. Under flow conditions, the nanorods with 96 nm show a maximum uptake efficiency by endothelial cells. This work demonstrates the importance of optimizing the size for improving the uptake efficiency of lanthanide-doped nanoparticles.

A Rh/Cu cocatalytic system for the synthesis of isoindolinones from N-methoxybenzamide and saturated ketones is established, which shows good compatibility with a broad range of substrates and functional groups.

A near zero thermal expansion NIR phosphor, AlP3O9:Cr3+, with high emission efficiency and excellent thermal stability is synthesized. A compact NIR pc-LED is fabricated and has a promising application in advanced nondestructive analysis technology.

The experimental and simulation results indicate that the reverse Brazil nut effect (RBNE)-Brazil nut effect (BNE) segregation inversion happens faster in the circular-bottom container than that in the flat-bottom container. The starting location of the sinkage of heavier grains at the top layer is triggered with certain randomness in the latter, whereas it first occurs at either of the lateral bottom edges in the former. The occurrence of standing-wave resonant spots of higher and lower granular temperature accelerates the RBNE-BNE transition. From the elastic collision model of single grain, the bottom with a larger angle leads to more energy transfer from the vertical direction. The simulation results of a monodisperse granular bed confirm that the circular-bottom container possesses a higher granular temperature and a lower packing density at the lateral edges of the circular bottom, whereas the flat-bottom container has a uniform standing-wave distribution with a period.

This study presents numerical simulations of the resonance of a finite-length granular chain of dissipative grains driven by a harmonically vibrated tube. Multiple gradual resonant modes, namely, non-resonance mode, partial-resonance mode, and complete-resonance mode, are identified. With a fixed vibration frequency, increased vibration acceleration leads to a one-by-one increase in the number of grains participating in resonance, which is equal to the number of grain-wall collisions in a vibration period. Compared with the characteristic time of the grain-grain and the grain-wall collisions, the time of free flight plays a dominant role in grain motion. This condition results in the occurrence of large opening gaps between the grains and independent grain-grain and gain-wall collisions. A general master equation that describes the dependence of the system energy on the length of the granular chain and the number of grain-wall collisions is established, and it is in good agreement with the simulation results. We observe a gradual step-jump increase in system energy when the vibration acceleration is continuously increased, which is dedicated to an individual energy injection. Moreover, two typical phase diagrams are discussed in the spaces of $\phi-\it{\Gamma}$ and $N-\it\Gamma$., Comment: 19 pages, 7 figures

All-inorganic cesium lead halide perovskite nanocrystals (CsPbX3, X = Cl, Br, I) have attracted considerable scientific and technological interest due to their precise bandgap tunability, high color purity and efficient luminescence. Nevertheless, their poor stability in harsh conditions such as moisture, ultraviolet (UV) light irradiation and high temperature, is a major obstacle for their further commercial applications. Herein, by simply using a new type of precursor, namely “HPbX3” (X = Cl, Br, I), we can achieve the coordination equilibrium for Pb precursors during reaction and obtain high-quality perovskite nanocrystals with tremendously enhanced luminous efficiency and chemical stability based on hot-injection method. The prepared α-CsPbI3 nanocrystals exhibit an extremely high photoluminescence quantum yield of 96% and keep stable in air for more than two months without any post-synthesis treatment. Moreover, stability evaluations under UV light irradiation, water or thermal impact are also performed and the results show substantially improved stability of these nanocrystals as compared with the samples prepared using traditional PbI2 as precursor. Through temperature-dependent (10–300 K) steady and transient spectral analysis combined with compositional measurements, it is revealed that the lower structural defect density, which is guaranteed by abundant halogen when using HPbX3 as precursor, is the most important reason for such performance enhancement.

Bifurcated granular flow in a 2D channel with two lateral exits is numerically investigated by the discrete element method. Under the fixed inflow rate condition, the outflow rate is equal to the inflow rate in the dilute flow state and rapidly declines when dilute-to-dense flow transition (DDFT) occurs. The flow rate and the transition can be controlled by adjusting the sizes of the two exits. These observations can be explained by the relationship between the flow rate and the packing density in the bottleneck region under the fixed grain condition. Beverloo's formula is valid to describe the dependence of the dense flow rate on the exit size for bifurcated and non-bifurcated granular flows. The packing density in the bottleneck region plays a crucial role on the flow state. In specific, DDFT occurs at 0.6, and the dense flow terminates at 0.79.

The giant interaction force between two neutral conducting spheres in an external electrical field was numerically investigated using the multiple image method. The simulation results coincide with the experimental results better than those using simple dipolar approximation and finite element analysis. For a small-inclined angle, the mutual induction leads to accumulation of unlike charges on the local adjacent surfaces of the spheres, thus producing a giant local electrical field compared with the external electrical field. The attractive force between the spheres is drastically increased. The interaction force peaks at [Formula: see text], where the center line of the spheres is parallel to the external electrical field. A weak repulsive force is found for a large-inclined angle because like charges concurrently appear on the local adjacent surfaces of the spheres. The nature of the attractive and repulsive interaction forces is independent of the radius ratio of the spheres. Analysis of influence of relative position of the spheres on the energy conversion showed that the shear stress could be improved by increasing the mutual electric potential energy and decreasing the interior electric potential energy. A maximum shear stress occurs at [Formula: see text], while the minimum mutual potential energy appears at [Formula: see text]. The discovery of interaction mechanism provides a plausible basis for fabricating new materials of giant electrorheological fluids.

Highly efficient and thermally stable broadband near-infrared (NIR) phosphors are urgently required for phosphor-converted light-emitting diodes (pc-LEDs), which are compact, low cost and promising for applications such as food analysis and agricultural science. Herein, a NIR phosphor, GdAl3(BO3)4:Cr3+ (GAB:Cr3+), with high emission efficiency and excellent thermal stability is presented. Under blue light excitation, GAB:Cr3+ shows a broad emission band covering 650–1000 nm with a full width at half maximum of ∼140 nm. Particularly, the 1.0 at% Cr3+ doped sample exhibits a photoluminescence (PL) quantum yield as high as 91%, and no decline of the PL intensity is observed even when the temperature is raised from 298 to 423 K. By combining the GAB:Cr3+ phosphor with a commercial blue LED chip, a high-performance NIR pc-LED is fabricated with a NIR radiant flux of 81 mW under a drive current of 350 mA. Furthermore, an aging test was performed on this device at 85 °C and 85% humidity for 480 h, and the radiant flux retained up to 95% of its initial value, which is comparable to the commercial phosphors. These results suggest that GAB:Cr3+ is a promising candidate for broadband pc-LEDs in NIR spectroscopy applications.

Halide segregation is a critical bottleneck that hampers the application of mixed-halide perovskite nanocrystals (NCs) in both electroluminescent and down-conversion red-light-emitting diodes. Herein, we report a strategy that combines precursor and surface engineering to obtain pure-red-emitting (peaked at 624 nm) NCs with a photoluminescence quantum yield of up to 92% and strongly suppresses the halide segregation of mixed-halide NCs under light irradiation. Red-light-emitting diodes (LED) using these mixed-halide NCs as phosphors exhibit color-stable emission with a negligible peak shift and spectral broadening during operation over 240 min. By contrast, a dramatic peak shift and spectral broadening were observed after 10 min of operation in LEDs based on mixed-halide NCs synthesized by a traditional method. Our strategy is critical to achieving photo- and band-gap-stable mixed-halide perovskite NCs for a variety of optoelectronic applications such as micro-LEDs.

Water and ions transport through graphene nanochannels has attracted considerable attention thanks to the possibility of dimensional control of the channel sizes down to single atomic layer. Using ...

Osmosis are essential for not only the application of nanofluidic devices but also the understanding of working principles of biological transmembrane proteins. Despite considerable experimental interests, comprehensive simulation work is still lacking, possibly because of the periodic boundary condition that inevitably leads to the spontaneous exchange of two side reservoirs. To eliminate this disadvantage, herein we design a simple model system by introducing a dipalmitoylphosphatidylcholine bilayer into a common carbon-nanotube (CNT)-based setup, which allows long-time osmotic simulations. Interestingly, the osmotic water flux exhibits an excellent linear relation with the concentration gradient and an Arrhenius relation with the temperature, which highly coincides with recent experimental observations. Furthermore, the osmotic flux can be quantitatively comparable to not only the experimental CNTs and protein channels but also the theoretical estimation from the Hagen-Poiseuille equation. The designed simulation model could open a new window for future studies on osmosis.

Persistent luminescence nanophosphors (PLNPs) emitting in the second near-infrared window (1000-1700 nm, NIR-II) are emerging as one promising class of in vivo bio-imaging agents due to their unique advantages including non-autofluorescence and low optical scattering in tissues. Currently, it remains a great challenge to synthesize nanosized lanthanide-doped inorganic NIR-II phosphors with a good persistent luminescence performance. Herein, we present a salt microemulsion method for synthesizing Ce3+, Cr3+, Nd3+ codoped Y3(Al/Ga)5O12 nanocrystals, which generate multi-wavelength persistent luminescence in the visible (∼508 nm, 5d1→ 4f of Ce3+), the first near-infrared window (∼890 nm, 4F3/2→4I9/2 of Nd3+) and NIR-II (∼1063 nm, 4F3/2→4I11/2 of Nd3+) regions. Under illumination of a 410 nm diode (3 W) for 10 min, the observed duration time of NIR-II persistent luminescence is as long as 60 min at room temperature. Moreover, the persistent luminescence can be excited efficiently by multiple excitation sources including a blue diode, white LEDs and an X-ray generator, which is crucial for deep tissue imaging applications. By comparing the penetration depth between NIR-I and NIR-II persistent luminescence through chicken breast, we prove that NIR-II photons exhibit a deeper optical penetration length (3.9 mm) than that of the NIR-I ones (2.5 mm). In addition, the NIR signals can still be detected 3 min after ceasing the excitation source by a small animal imaging system (InGaAs detector) when the thickness of the covering chicken breast is 20 mm. These results show great promise for Y3(Al/Ga)5O12:Ce3+,Cr3+,Nd3+ nanocrystals as a PLNP for bio-imaging applications with deep penetration depth and a high signal-to-noise ratio.

K2 TiF6 :Mn4+ is a highly efficient narrow-band emission red phosphor with promising applications in white light-emitting diodes (LEDs) and wide-gamut displays. Nevertheless, the poor moisture-resistant properties of this material hinder commercialization. A convenient reverse cation-exchange strategy is introduced for constructing a core-shell-structured K2 TiF6 :Mn4+ @K2 TiF6 phosphor. The outer K2 TiF6 shell acts as a shield for preventing moisture in the air from hydrolyzing the internal MnF62- group, while effectively cutting off the path of energy migration to surface defects, thereby increasing the emission efficiency (especially for the phosphors doped with high concentrations of Mn4+ ). Employed as a red phosphor, the packaged white LED exhibits an extraordinarily high luminous efficacy of 162 lm W-1 , a correlated color temperature (CCT) of 3510 K, and a color rendering index of 93 (Ra ). Aging tests performed on this device at 85 °C and 85 % humidity for 480 h retain up to 89 % luminous efficacy. The findings could facilitate commercial application of K2 TiF6 :Mn4+ @K2 TiF6 phosphor.

Owing to few thermal populations or spectral absence at extreme low temperature, fluorescence intensity ratio (FIR) technique based on thermal coupling levels is sometimes unpractical for low temperature sensing. Herein, using bandwidth as a sensing parameter, the low temperature sensing performances of YOF:Yb3+/Tm3+ phosphor are reported. The YOF:10%Yb3+/0.2%Tm3+ phosphor is prepared by hydrothermal and calcined methods. Under 980 nm excitation, the temperature dependent upconversion spectra are recorded in the range of 12–300 K, and the temperature sensing behaviors are investigated in detail. The phosphor exhibits a single-band near-infrared (NIR) luminescence composed of multiple narrow peaks. Thereinto, the ultranarrow bandwidths of 12,485 cm−1 (800.9 nm) and 12,580 cm−1 (794.9 nm) emission bands are only 14 cm−1 (0.9 nm) and 12 cm−1 (0.75 nm) at 12 K, respectively. Based on temperature dependent bandwidth, the maximum relative sensitivities are found to be 0.60% K−1 (12–190 K) and 0.84% K−1 (190–300 K), which enable the YOF:10%Yb3+/0.2%Tm3+ phosphor to be a promising thermometer for low temperature sensing.

In this text, a laboratory-scale A