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The all‐inorganic metal halide perovskite CsPbX3 (X = Cl, Br, and I) has received extensive attention in the field of white light‐emitting diodes (WLEDs) due to its high luminous intensity and high color purity. However, the shortcoming of poor stability directly affects the luminous performance of the WLED devices and reduces their luminous efficiency, which has become an urgent problem to be solved. Here, three‐color lead halide perovskite phosphors (blue‐emitting CsPbBr3 synthesized at 20 °C (CPB‐20), green‐emitting CsPbBr3‐80 (CPB‐80)/CsPbBr3:SCN−(CPB:SCN−), and red‐emitting PEA2PbBr4 (PPB)/PEA2PbBr4:Mn2+ (PPB:Mn2+)) with higher stability and luminous intensity are simultaneously prepared and applied in WLEDs. Density functional theory is used to optimize the structures of CsPbBr3 and PEA2PbBr4, and to calculate the work function, optical properties, and charge density difference. Not only the WLED devices with three‐color lead halide perovskite phosphors are constructed, but also WLED devices from warm white to cold white are realized by tuning the ratio of the different emissions, and a superior color quality (color rendering index of 96) and ideal correlated color temperature (CCT of 9376 K) are achieved. This work will set the stage for exploring low‐cost, environmentally friendly, high‐performance WLEDs. [ABSTRACT FROM AUTHOR]

The effect of rare earth (RE) single atoms on photocatalytic activity is very complex due to its special electronic configuration, which leads to few reports on the RE single atoms. Here, Dy3+ single atom composite photocatalysts are successfully constructed based on both the special role of Dy3+ and the special advantages of CdS/g‐C3N4 heterojunction in the field of photocatalysis. The results show that an efficient way of electron transfer is provided to promote charge separation, and the dual functions of CO2 molecular activation of rare‐earth single atom and 4f levels as electron transport bridge are fully exploited. It is exciting that under visible‐light irradiation, the catalytic performance of CdS:Dy3+/g‐C3N4 is ≈6.9 times higher than that of pure g‐C3N4. The catalytic performance of CdS:Dy3+ and CdS:Dy3+/g‐C3N4 are ≈7 and ≈13.7 times higher than those of pure CdS, respectively. Besides, not all RE ions are suitable for charge transfer bridges, which is not only related to the 4f levels of RE ions but also related to the bandgap structure of CdS and g‐C3N4. The pattern of combining single‐atom catalysis and heterojunction opens up new methods for enhancing photocatalytic activity. [ABSTRACT FROM AUTHOR]

Only when the interfacial charge separation is enhanced and the CO2 activation is improved, can the heterojunction nanocomposite photocatalyst be brought into full play for the CO2 reduction reaction (CO2RR). Here, Er3+ single atom composite photocatalysts were successfully constructed based on both the special role of Er3+ single atoms and the special advantages of the SrTiO3:Er3+/g-C3N4 heterojunction in the field of photocatalysis for the first time. As we expected, the SrTiO3:Er3+/g-C3N4 (22.35 and 16.90 μmol g−1 h−1 for CO and CH4) exhibits about 5 times enhancement in visible-light photocatalytic activity compared to pure g-C3N4 (4.60 and 3.40 μmol g−1 h−1 for CO and CH4). In particular, the photocatalytic performance of SrTiO3:Er3+/g-C3N4 is more than three times higher than that of SrTiO3/g-C3N4. From Er3+ fluorescence quenching measurements, photoelectrochemical studies, transient PL studies and DFT calculations, it is verified that a small fraction of surface doping of Er3+ formed Er single-atoms on SrTiO3 building an energy transfer bridge between the interface of SrTiO3 and g-C3N4, resulting in enhanced interfacial charge separation. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC HAADF-STEM) and adsorption energy calculations demonstrated that the exposed Er single-atoms outside the interface on SrTiO3 preferentially activate the adsorbed CO2, leading to the high photoactivity for the CO2RR. A novel enhanced photocatalytic mechanism was proposed, in which Er single-atoms play dual roles of an energy transfer bridge and activating CO2 to promote charge separation. This provides new insights and feasible routes to develop highly efficient photocatalytic materials by engineering rare-earth single-atom doping. [ABSTRACT FROM AUTHOR]

Potassium azide was investigated by Raman scattering spectroscopy up to a pressure of 55.0 GPa by use of diamond anvil cell at room temperature. A pressure-induced reversible phase transition was revealed. The onset of the phase transition was characterized by the hardening of a previously soft lattice mode at 13.6 GPa. This transition is considered a structural phase transition. Compression induces a symmetry reduction, which is indicated by the splitting of the librational modes, the development of infrared active vibrational modes, and the appearance of other new modes in the external mode region. The new high-pressure phase, with azide ions still in a molecular state, can be preserved down to 1.2 GPa. The Grüneisen parameters for the parent phase were calculated. [ABSTRACT FROM AUTHOR]

Silver azide (AgN3) was compressed up to 51.3 GPa. The results reveal a reversible second-order orthorhombic-to-tetragonal phase transformation starting from ambient pressure and completing at 2.7 GPa. The phase transition is accompanied by a proximity of cell parameters a and b, a 3° rotation of azide anions, and a change of coordination number from 4-4 (four short, four long) to eight fold. The crystal structure of the high pressure phase is determined to be in I4/mcm space group, with Ag at 4a, N1 at 4d, and N2 at 8h Wyckoff positions. Both of the two phases have anisotropic compressibility: the orthorhombic phase exhibits an anomalous expansion under compression along a-axis and is more compressive along b-axis than c-axis; the tetragonal phase is more compressive along the interlayer direction than the intralayer directions. The bulk moduli of the orthorhombic and tetragonal phases are determined to be KOT = 39 ± 5 GPa with KOT' = 10 ± 7 and KOT = 57 ± 2 GPa with KOT' = 6.6 ± 0.2, respectively. [ABSTRACT FROM AUTHOR]

The crystal structure and equation of state (EOS) of aluminum carbide (Al4C3) have been determined directly up to 50.1 GPa at room temperature by the synchrotron x-ray diffraction techniques. The results indicate that Al4C3 remained in rhombohedral structure under all tested pressure-temperature conditions and exhibited anisotropic compressibility, with the c-axis more compressible than the a-axis. Fitting the experimental data to third order Birch–Murnaghan EOS yields a bulk modulus of KOT=233±6 GPa with its pressure derivative KOT′=3.4±0.4, while the second-order EOS yields KOT=223±2 GPa. [ABSTRACT FROM AUTHOR]

Nanocrystalline silicon carbide (SiC) with a diameter of 7 nm was synthesized in a high voltage electrical explosion. It has a larger lattice parameter (0.1%) than its bulk material. Synchrotron x-ray diffraction measurements of nanocrystalline SiC were carried out to 15.8 GPa. The bulk modulus was determined to be K0T=201±10 GPa, which is substantially smaller than those of bulk material and nanocrystalline with large grain sizes. It is considered to be caused by the weaker atomic bonding strength and the imperfections of the nanocrystalline SiC. [ABSTRACT FROM AUTHOR]

All-nitrogen anions have attracted extensive attention because of their unique chemical and physical properties, and potential applications as high-energy density materials. Here, we discovered two N44- anions with planar zigzag and tripodal structures in BeN2 compound using first-principle calculations with structural search. At ambient conditions, both of them have high kinetic and thermodynamic stability with high energy density (2.48 kJ/g, and 2.95 kJ/g relative to Be3N2 and N2 gas). The zigzag N44− anion has P21/c space group in BeN2 compound and is energetically favorite in the pressure range of 0−48 GPa. While tripodal N44− anion has Cm space group and is energetically favorite in the pressure range of 48−100 GPa. Further analysis of chemical bonding pattern and electronic properties show that the Be atoms provide 2s electrons to alter the bonding state of N44− as well as use empty outer shell 2p orbital to accommodate lone pair electrons of N atoms, forming coordinate bonds to stabilize the compounds. More important, the calculated formation of enthalpies indicate that the zigzag and tripodal N44− can be synthesized via compressing Be3N2 and N2 at a modest pressure. Our results provide a scheme to synthesis N44- anions and stabilize all-nitrogen anions by introducing beryllium atoms. [ABSTRACT FROM AUTHOR]

Recently, a novel two-dimensional (2D) metal-free organic material, the C4N3H monolayer, has been proposed and predicted to be a 2D Dirac material with high Fermi velocities. Herein, we investigated its mechanical properties and tensile strain effects on its electronic properties based on first-principles calculations. We demonstrated that this material is quite soft with small stiffness constants and can sustain large strains. Compared to many other 2D materials, this material presents a remarkable elastic anisotropy and a large Poisson's ratio, which are very important for strain engineering. We also found that the Dirac cone of this material is very robust against the tensile strains and the Fermi velocity is high. The small stiffness constant, large Poisson's ratio, robust Dirac cone, and high Fermi velocity make the C4N3H monolayer a promising material in high-speed flexible electronic devices. [ABSTRACT FROM AUTHOR]

All-nitrogen salts have attracted much attention because of their potential applications as high-energy density materials for explosive or propulsion. Here, we design a cage-like salt Be3N10 with pure N-N single bonds via releasing the pressure of the cage-like diamondoid "N10", high-pressure phase of nitrogen, and introducing beryllium atoms to stabilize the crystal. At ambient conditions, Be3N10 comprises two anions and six Be2+ cations in a unit cell with high space symmetry (space group). The Be3N10 salt is kinetically and thermodynamically stable with a 3.06 eV band gap at 0 GPa and room temperature. Further analysis of the chemical bonding pattern and electronic properties reveals that the introduced Be atoms contribute electrons to passivate the dangling bonds of the N10 cluster, and stabilize the system through both Coulomb interactions and covalent bonds. The outstanding properties, including high-energy density (5.75 kJ/g), high nitrogen content (83.8%), and high dynamical stability, make Be3N10 a promising high-energy density material. Our work represents a significant step toward the all-nitrogen salt with pure N-N single bonds. [ABSTRACT FROM AUTHOR]