Numerical simulations of dense granular flow in a two-dimensional channel:The role of exit position

Molecular dynamics simulations have been performed to elucidate the influence of exit position on a dense granular flow in a two-dimensional channel. The results show that the dense flow rate remains constant when the exit is far from the channel wall and increases exponentially when the exit moves close to the lateral position. Beverloo’s law proves to be successful in describing the relation between the dense flow rate and the exit size for both the center and the lateral exits.Further simulated results confirm the existence of arch-like structure of contact force above the exit. The effective exit size is enlarged when the exit moves from the center to the lateral position. As compared with the granular flow of the center exit, both the vertical velocities of the grains and the flow rate increase for the lateral exit.

Organic polystyrene and inorganic silica double shell protected lead halide perovskite nanocrystals with high emission efficiency and superior stability

The practical application of all-inorganic semiconductor lead halide perovskite nanocrystals(LHP NCs)has been limited by their poor stability.Recently,a lot of research on core-shell structure has been done to improve the stability of perovskite NCs,but the effect was far from the application requirements.Herein,we,for the first time,report a convenient approach to synthesize organic-inorganic double shell CsPbBr_(3)@SiO_(2)@polystyrene(PS)NCs with an inter-core of CsPbBr_(3),the intermediate layer of SiO_(2)shell,and outmost PS shell.Particularly,the CsPbBr_(3)@SiO_(2)@PS NCs maintained more than 90%of their initial photoluminescence(PL)intensity under one month's ultraviolet lamp irradiation or in 85℃ and 85%relative humidity(RH)condition.The white-light-emitting-diodes(WLEDs)were fabricated by encapsulating commercial InGaN chip with CsPbBr_(3)@SiO_(2)@PS NCs and K2SiF6:Mn^(4+)(KSF:Mn^(4+))phosphor with a luminous efficacy of~100 lm/W at 20 mA current and a color gamut of 128%of the National Television Standards Committee(NTSC)standard.In addition,these WLEDs still maintain 91%of the initial luminous efficacy after 1200 h of continuous lighting.These results demonstrated that double shell-protected CsPbBr_(3)perovskite NCs have great potential in the field of WLEDs.

Synthesis of NaYF_(4):20% Yb^(3+),2% Er^(3+),2% Ce^(3+)@NaYF_(4) nanorods and their size dependent uptake efficiency under flow condition

Lanthanide doped fluorescent 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 NaYF_(4):20%Yb^(3+),2%Er^(3+),2%Ce^(3+)(the contents of rare earths elements are in molar fraction)nanoparticles as core,NaYF_(4):20%Yb^(3+),2%Er^(3+),2%Ce^(3+)@NaYF_(4) core-shell structured nanorods(NRs)with different sizes of 60-224 nm were synthesized by thermal decomposition and hot injection method.Under excitation at 980 nm,a strong upconversion green emission(541 nm,^(2)H_(11/2)→^(4) I_(15/2) of Er^(3+))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.

Precursor chemistry towards highly efficient and phase-stable red emitting CsPbI_(3) perovskite nanocrystals

All-inorganic cesium lead halide perovskite nanocrystals(CsPbX_(3),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“HPbX_(3)”(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 a-CsPbb 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 Pbl_(2) 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.