Herein, we report the design of novel ultraviolet luminescent CsPbCl3 nanocrystals (NCs) with the emission peak at 381 nm through doping of cadmium ions. Subsequently, a surface passivation strategy ...with CdCl2 is adopted to improve their photoluminescence quantum yield (PLQY) with the maximum value of 60.5 %, which is 67 times higher than that of the pristine counterparts. The PLQY of the surface passivated NCs remains over 50 % after one week while the pristine NCs show negligible emission. By virtue of density functional theory calculations, we reveal that the higher PLQY and better stability after surface passivation may result from the significant elimination of surface chloride vacancy (VCl) defects. These findings provide fundamental insights into the optical manipulation of metal ion‐doped CsPbCl3 NCs.
UV‐emitting halide perovskites are designed by doping Cd2+ into CsPbCl3 nanocrystals to broaden their band gap with the emission peak at 381 nm. Upon treatment with CdCl2, a UV photoluminescence quantum yield up to 60.5 % can be achieved. Transient absorption spectra and first‐principle calculations confirm that the significantly improved optical performance benefits primarily from the marked elimination of surface traps such as a Cl vacancy.
The Nb3Al superconductor with excellent physical and working properties is one of the most promising materials in high-magnetic-field applications. However, it is difficult to prepare high-quality ...Nb3Al with a desired superconducting transition temperature (Tc) because of its narrow phase formation area at high temperatures (>1940 °C). This work reports a method to prepare stoichiometric Nb3Al powder samples at a relatively low temperature (1400 °C) by exploiting the nano effect of Nb particles with pretreatment of Nb powder under H2/Ar atmosphere. The obtained Nb3Al samples exhibit high Tc’s of ~16.8K. Based on density functional theory (DFT) calculations and statistical mechanics analysis, the crucial role of quantum effect in leading to the success of the preparation method was studied. A new measure of surface energy (MSE) of a model particle is introduced to study its size and face dependence. A rapid convergence of the MSE with respect to the size indicates a quick approach to the solid limit, while the face dependence of MSE reveals a liquid-like behavior. The surface effect and quantum fluctuation of the Nbn clusters explain the success of the preparation method.
The development in materials science and pharmaceutics shows that there exist some key materials genomes, i.e., certain groups of atoms with specific constituents and structures, which govern the ...property of a series of materials based on them. To pinpoint such materials, genomes are helpful to assemble functional units and synthesize new materials and, thus, have a profound meaning. In this work, we develop an innovative method based on the idea of projecting atomic orbitals’ wavefunction, which enables us to project every physical quantity into their orbital contribution and, thus, can be widely used to identify the materials genomes of various properties. Within this framework, we derive the expressions of the projected optical susceptibilities and exhibit a paradigm of studying the corresponding materials genomes of optical properties, especially the desired nonlinear optical materials.
The second harmonic generation (SHG) responses of the paraelectric and ferroelectric phases of KH2PO4 (KDP) were calculated by first-principles density functional theory (DFT) calculations, and the ...individual atom contributions to the SHG responses were analyzed by the atom response theory (ART). We show that the occurrence of static polarization does not enhance the SHG responses of the ferroelectric KDP, and that the Kleinman symmetry is reasonably well obeyed for the paraelectric phase, but not for the ferroelectric phase despite that the latter has a larger bandgap. This is caused most likely by the fact that the ferroelectric phase has lower-symmetry local structures than does the paraelectric phase. The contribution to the SHG response of an individual K+ ion is comparable to that of an individual O2− ion. The contributions of the O2− and K+ ions arise overwhelmingly from the polarizable parts of the electronic structure, namely, from the valence bands of the O-2p nonbonding states and from the conduction bands of the K-3d states.
It is a significant challenge to enhance the band alignment sensitivity of MoS
2
-based optoelectronic devices by constructing semiconductor heterojunction. To solve the problem, we incorporate Cu
2
...O into MoS
2
to enhance the tunability of electronic structures for the first time by controlling interlayer spacings or electric field (
E
field
) using first-principles calculations. A stable van der Waals heterojunction forms between Cu
2
O and MoS
2
based on the negative interfacial cohesive energy and the excellent lattice match. Noteworthily, the bandgap of Cu
2
O/MoS
2
heterojunction varies about 0.2–0.3 eV with a 0.1 V/Å increase of
E
field
, which is more sensitive than that of pure MoS
2
. It is confirmed that the inhomogeneous charge redistribution of heterojunction enhances the tunability of electronic structures. Additionally, the detection wavelength of heterojunction expands from visible to infrared spectrum with
E
field
. These findings motivate more theoretical and experimental work to further study photodetectors with high sensitivity and low power consumption.
Graphical abstract
A domain of locations of a proton in the perovskite structure is determined by studying the local structure and a hard sphere point charge model. Two intra‐ and one inter‐octahedron processes with ...different energy barriers of ⟨E1⟩, ⟨E2⟩, and ⟨E3⟩ have been studied, respectively. The order of the energy barriers is predicted as ⟨E3⟩ > ⟨E1⟩ ≥ ⟨E2⟩ by studying both the changes of bonding in these processes and the charge imbalance between the acceptor dopant ion and the B type ion. The inter‐octahedron hopping, ⟨E3⟩, is shown to be a necessary and rate limiting step by using percolation and charge imbalance argument. This result differs with earlier calculations, however, it agrees with the result of quasi‐elastic neutron and other experimental results. Through studying the lattice dynamics of a 1D O–H chain and its monomer, we have developed new formulae for a hydrogen bond system and applied them to explain the experimentally observed red‐shift and broadening of the O–H vibration peak. These phenomena are revealed as indications of the quasi‐free state of a proton instead of the formation of hydrogen bond.
First-principles calculations based on the density functional theory (DFT) were carried out to study the atomic structure and electronic structure of LiAl2(OH)6Cl, the only material in the layered ...double hydroxide family in which delithiation was found to occur. Ab initio molecular dynamics (AIMD) simulations were used to explore the evolution of the structure of LiAl2(OH)6Cl during a thermally induced delithiation process. The simulations show that this process occurs due to the drastic dynamics of Li+ at temperatures higher than ~450 K, in which the Al2(OH)6 host layers remain stable up to 1100 K. The calculated large value of the Li+ diffusion coefficient D, ~ 3.13 × 10 − 5 c m 2 / s , at 500 K and the high stability of the Al2(OH)6 framework suggest a potential technical application of the partially-delithiated Li1-xAl2(OH)6Cl1-x (0 < x < 1) as a superionic conductor at high temperatures.
The onsite repulsion, spin-orbit coupling and polarizability of elements and their ions play important roles in controlling the physical properties of molecules and condensed materials. In ...celebration of the 150th birthday of the periodic table this year, we briefly review how these parameters affect the physical properties and are interrelated.
The damage of first wall material in fusion reactor due to the bubbles caused by plasma has been studied by introducing a relation between the von Mises equivalent stress and the temperature field. ...The locations and shapes of the bubbles and the synergetic effect between the different bubbles under steady operational conditions have been studied using the finite elements method. Under transient heat loads, plastic deformations have been found to occur, and are significantly enhanced by the presence of the bubbles. The calculated concentration locations of von Mises equivalent stress are well consistent with the observed crack positions of the tungsten surface in many test experiments. Our simulations show that the damage of the bubbles is not severe enough to lead to catastrophic failure of the tungsten armor; however, it can cause local and gradual detachment of tungsten surface, which provides a reasonable explanation for the observed pits and rough or hairy surface morphology etc. Considering the transient heat loads, the lower bound of the security thickness of the tungsten tile is estimated to be greater than 2 mm.
When doped with oxygen, the layered Y2O2Bi phase becomes a superconductor. This finding raises questions about the sites for doped oxygen, the mechanism of superconductivity, and practical guidelines ...for discovering new superconductors. We probed these questions in terms of first‐principles calculations for undoped and O‐doped Y2O2Bi. The preferred sites for doped O atoms are the centers of Bi4 squares in the Bi square net. Several Bi 6p x/y bands of Y2O2Bi are raised in energy by oxygen doping because the 2p x/y orbitals of the doped oxygen make antibonding possible with the 6p x/y orbitals of surrounding Bi atoms. Consequently, the condition necessary for the “flat/steep” band model for superconductivity is satisfied in O‐doped Y2O2Bi.
Ripples in the Dirac Sea: Density functional calculations reveal that the preferred sites for oxygen doping in Y2O2Bi are the centers of the Bi4 squares in bismuth nets. Oxygen doping of Y2O2+δBi satisfies the conditions of the “flat/steep” band model for superconductivity.
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