Bright and stable blue emitters with narrow full‐width at half‐maxima are particularly desirable for applications in television displays and related technologies. Here, this study shows that doping aluminum (Al3+) ion into CsPbBr3 nanocrystals (NCs) using AlBr3 can afford lead‐halide perovskites NCs with stable blue photoluminescence. First, theoretical and experimental analyses reveal that the extended band gap and quantum confinement effect of elongated shape give rise to the desirable blueshifted emission. Second, the aluminum ion incorporation path is rationalized qualitatively by invoking fundamental considerations about binding relations in AlBr3 and its dimer. Finally, the absence of anion‐exchange effect is corroborated when green CsPbBr3 and blue Al:CsPbBr3 NCs are mixed. Combinations of the above two NCs with red‐emitting CdSe@ZnS NCs result in UV‐pumped white light‐emitting diodes (LED) with an National Television System Committee (NTSC) value of 116% and ITU‐R Recommendation B.T. 2020 (Rec. 2020) of 87%. The color coordinates of the white LED are optimized at (0.32, 0.34) in CIE 1931. The results suggest that low‐cost, earth‐abundant, solution‐processable Al‐doped perovskite NCs can be promising candidate materials for blue down‐conversion layer in backlit displays.

Wearable pressure sensors with high sensitivity, broad dynamic response range and low detection limit are highly desirable to enable the applications in electronic skins and soft robotics. In this work, we report a high-performance wearable pressure sensor based on microstructured polydimethylsiloxane (PDMS)/Ag and rough polyimide (PI)/Au interdigital electrodes. By tailoring the touchpoints, the resulting pressure sensors show ultrahigh sensitivity (259.32 kPa -1 ), broad dynamic response range (54 kPa) and low detection limit (0.36 Pa). We also systematically investigate the effect of different sensor structural configurations, PDMS geometrical feature, and Ag thickness on the performance of the pressure sensors. Thanks to these merits, the fabricated pressure sensor is capable of real-time monitoring pulse wave, and can act as a part of the mechanical hand to detect weak pressure changes, leading to the great application promise in the fields of biomedical, real-time health monitoring and intelligent robot.

For Li 2 FeSiO 4 , its P2 1 space group makes it possibly perfect as a new cathode material for Li-ion batteries (Nishimura et al. J. Am. Chem. Soc. 2008, 130, 13212). For this type of Li 2 MSiO 4 (M ) Mn, Fe, and Co), the structural, electronic, and electrochemical properties have been investigated, using the density functional theory with the exchange-correlation energy treated as the generalized gradient approximation (GGA) plus on-site Coulomb energy correction (+U). Within the GGA+U framework, the fully lithiated Li 2 MSiO 4 as well as the delithiated LiMSiO 4 and MSiO 4 are all semiconducting, and the band gap lowers with the extraction of lithium ions. The fully lithiated compounds are all stabilized at their ferromagnetic phase, while the delithiated compounds are all stabilized when antiferromagnetic. Starting from the P2 1 structure, the fully delithiated MSiO 4 has better stability than that obtained from Pmn2 1 structure. In Li 2 FeSiO 4 , the possibility of reversibly extracting more than one lithium ion is enhanced because of the lower stability of the intermediate phase LiFeSiO 4 comparing with the Pmn2 1 symmetry situation. Li 2 MnSiO 4 with the P2 1 symmetry has higher electronic conductivity, and Li 2 CoSiO 4 has the suitable second-step voltage of less than 5.0 V. All Li 2 FeSiO 4 , Li 2 MnSiO 4 , and Li 2 CoSiO 4 are predicted as promising cathode materials.

Recently, there is a series of reports by Wang et al. on the superconductivity in K-doped pterphenyl (KxC18H14) with the transition temperatures range from 7 to 123 Kelvin. Identifying the structural and bonding character is the key to understand the superconducting phases and the related properties. Therefore we carried out an extensive study on the crystal structures with different doping levels and investigate the thermodynamic stability, structural, electronic, and magnetic properties by the first-principles calculations. Our calculated structures capture most features of the experimentally observed X-ray diffraction patterns. The K doping concentration is constrained to within the range of 2 and 3. The obtained formation energy indicates that the system at x = 2.5 is more stable. The strong ionic bonding interaction is found in between K atoms and organic molecules. The charge transfer accounts for the metallic feature of the doped materials. For a small amount of charge transferred, the tilting force between the two successive benzenes drives the system to stabilize at the antiferromagnetic ground state, while the system exhibits non-magnetic behavior with increasing charge transfer. The multiformity of band structures near the Fermi level indicates that the driving force for superconductivity is complicated.

Hydrogen-rich materials have fascinating physical and chemical properties such as various structures and superconductivity under high-pressure. In this study, structural, electronic, dynamical, and superconducting properties of GeH 4 (H 2 ) 2 are investigated based on the first-principles calculations. We first predict several phase transitions of GeH 4 (H 2 ) 2 under pressure. Below 28 GPa, two degenerated structures with I4̅ m2 and Pmn2 1 symmetries are preferred, which can be viewed as the distortion of the experimentally observed fcc structure. Then, the GeH 4 (H 2 ) 2 , via a triclinic phase that stabilizes in the pressure range of 28−48 GPa, transforms into a metallic orthorhombic phase in which appears the metallization induced by pressure. Another metallic phase with P2 1 /c symmetry enters the phase diagram at around 220 GPa, which is more stable than the case of a decomposed material, and its stability is also confirmed by including the zero point energy correction. In the high-pressure P2 1 /c phase, the superconductivity is found, and the superconducting transition temperature is predicted to be as high as 76−90 K at 250 GPa. This superconductivity mainly results from the local vibrations of more H 2 units, though the vibration of Ge in an H 2 -formed grid also contributes to the electron−phonon interaction. This study is helpful for understanding the superconducting mechanism on hydrogen-rich compounds.

We present the properties of a large sample (12 282) of nearly face‐on low surface brightness (LSB) disc galaxies selected from the main galaxy sample of SDSS‐DR4. These properties include B‐band central surface brightness μ0(B), scalelengths h, integrated magnitudes, colours and distances D. This sample has μ0(B) values from 22 to 24.5 mag arcsec−2 with a median value of 22.42 mag arcsec−2, and disc scalelengths ranging from 2 to 19 kpc. They are quite bright with MB taking values from −18 to −23 mag with a median value of −20.08 mag. There exist clear correlations between log h and MB, log h and log D, log D and MB. However, no obvious correlations are found between μ0(B) and log h, colours, etc. The correlation between colours and log h is weak even though it exists. Both the optical–optical and optical–NIR colour–colour diagrams indicate that most of them have a mixture of young and old stellar populations. They also satisfy colour–magnitude relations, which indicate that brighter galaxies tend generally to be redder. The comparison between the LSBGs and a control sample of nearly face‐on disc galaxies with higher surface brightness (HSB) with μ0(B) from 18.5 to 22 mag arcsec−2 show that, at a given luminosity or distance, the observed LSB galaxies tend to have larger scalelengths. These trends could be seen gradually by dividing both the LSBGs and HSBGs into two subgroups according to surface brightness. A volume‐limited subsample was extracted to check the incompleteness of surface brightness. The only one of the property relations having an obvious change is the relation of log h versus μ0(B), which shows a correlation in this subsample.

Based on the density functional theory with hybrid functional approach, we have studied the structural and thermodynamic stabilities of Cu2M SnX4 (M = Zn, Mg, and Ca; X = S and Se) alloy, and have further investigated the electronic and optical properties of stable Cu2MgSnS4 and Cu2MgSnSe4 phases. Thermal stability analysis indicates that Cu2MgSnS4 and Cu2MgSnSe4 are thermodynamically stable, while Cu2CaSnS4 and Cu2CaSnSe4 are unstable. The ground state configuration of the compound changes from kesterite into stannite structure when Zn atoms are substitued by larger Mg or Ca atoms. An energy separation between stannite and kesterite phase similar to that of CZTS is observed. Calculated electronic structures and optical properties suggest that Cu2MgSnS4 and Cu2MgSnSe4 can be efficient photovoltaic materials. arXiv:1509.06230v2 [cond-mat.mtrl-sci] 3 Dec 2015

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