Transition probabilities of the X1Σ+, A1Π, B1Δ, C1Σ+, and D1Π states of the AlO+ cation

ABSTRACT

This study computes the potential energy curves of the X¹Σ⁺, A¹Π, B¹Δ, C¹Σ⁺, and D¹Π states of AlO⁺ cation and the transition dipole moments between them. The orders of the rotationless radiative lifetimes are 10–100?μs for the A¹Π state, 1–1000?ms for the B¹Δ state, 10?ns for the first well and 100?ns for the second well of the C¹Σ⁺ state, and 1?μs for the D¹Π state. Emissions of the B¹Δ–A¹Π and D¹Π–C¹Σ⁺ systems are so weak that they are hardly measured via spectroscopy, the emissions of the C¹Σ⁺–X¹Σ⁺, C¹Σ⁺–A¹Π, and D¹Π–X¹Σ⁺ systems are so strong that they can be detected readily, and emissions of the A¹Π–X¹Σ⁺ and D¹Π–A¹Π systems can be observed through spectroscopy only by a significant effort. There is a strong great similarity between spontaneous emissions of the A¹Π–X¹Σ⁺ system of the AlO⁺ cation and the A²Π–X²Σ⁺ system of the AlO radical. The emissions of the A²Π–X²Σ⁺ system of the AlO radical have been measured in outer space Therefore, it is highly possible that the emissions of the A¹Π–X¹Σ⁺ system of the AlO⁺ cation can be detected in the astrophysical media.     

Properties of RhP predicted by first-principles

Using density functional theory combined with a global crystal structure search with the particle swarm optimization method, we propose three stable three-dimensional (3D) metallic RhP structures, namely, the Cmcm (RhP-I), P6/mmm (RhP-II), and P6₃mc (RhP-III) phases. All these structures are found to be dynamically stable through vibrational normal mode calculations, indicating that they could be successfully synthesized in experiments. We show that the RhP-I phase has a relatively high thermodynamic stability and high mechanical strength in comparison with the others. The RhP-II and RhP-III phases have porous structures which could accommodate small atoms or molecules. However their thermodynamics are poor, especially the RhP-III phase. The RhP-II structure is stable at 500 K, but the RhP-III fails to survive even at the freezing point of water. Importantly, all these materials have one dimensional conducting channels corresponding to ultrahigh Fermi velocities. Moreover, the porous hexagonal RhP-II and III structures exhibit excellent ability to trap lithium, hydrogen, oxygen, and boron atoms. The RhP-II structure could be especially useful for directly dissociating the hydrogen molecule into two atoms without an energy barrier. In the present study, we identify three new metallic structures to the family of RhP structures, and anticipate their potential for technological applications.     

面内双轴应力作用下单层黑磷能带性质研究

通过第一性原理对平面内双轴应力作用下的单层黑磷能带结构进行了计算.双轴拉伸应力作用下单层黑磷始终保持直接带隙性质,双轴压缩应力作用下的单层黑磷则发生了直接带隙转变为间接带隙的现象,当双轴压缩应力增加到7%时单层黑磷带隙闭合.     

Electronic and optical properties of Sr3X2 (X=N,P, As,Sb and Bi) compounds: first principles study

ABSTRACT

Direct bandgap semiconductors are very essential to fulfil the demand for the advancement in optoelectronic devices. Therefore it is important to predict new potential candidates having such unique features. In current work, Sr₃X₂ (X=N, P, As, Sb and Bi) compounds have been reported for the first time by well trusted FP-APW+lo method. For the better prediction of the energy band gap, mBJ is used alongwith routine generalised gradient approximation (GGA). The results show small and direct energy band gaps at Γ-Γ symmetry points with magnitude in the range from 0.62?eV (Sr₃P₂) to zero energy band gap (Sr₃Bi₂). In partial density of state Sr-d state and X-p state are contributed in the band structure. The compounds show mostly covalent bonding nature. The frequecy dependent optical properties in the linear optical range are also investigated.     

Influence of solvent on solution processed Cu2ZnSnS4 nanocrystals and annealing induced changes in the optical,structural properties of CZTS film

The well-known quaternary Cu₂ZnSnS₄ (CZTS) chalcogenide thin films are playing an important role in modern technology. The CZTS nanocrystal were successfully prepared by solution method using water, ethylene glycol and ethylenediamine as different solvent. The pure phase material was used for thin film coating by thermal evaporation method. The prepared CZTS thin films were characterized by XRD, Raman spectroscopy, FESEM, XPS and FT-IR spectroscopy. The XRD and Raman spectroscopy analysis revealed the formation of polycrystalline CZTS thin film with tetragonal crystal structure after annealing at 450 ^°C. The oxidation state of the annealed film was studied by XPS. A direct band gap about 1.36 eV was estimated for the film from FT-IR studies, which is nearly close to the optimum value of band gap energy of CZTS materials for best solar cell efficiency. The CZTS annealed thin films are more suitable for using as a p-type absorber layer in a low-cost solar cell.     

Er3Pd7P4 — Kristallstrukturbestimmung und Extended Hückel Rechnungen

Er₃Pd₇P₄ — Crystal Structure Determination and Extended Hückel Calculations Er₃Pd₇P₄ was prepared by heating the elements (1050°C) and investigated by means of single-crystal X-ray methods. The compound crystallizes in a new structure (C2/m; a = 15.180(3) Å, b = 3.955(1) Å, c = 9.320(1) Å, β = 125,65(1)°; Z = 2) with a three-dimensional framework of Pd and P atoms and with Er atoms in the holes. The Pd atoms are surrounded tetrahedrally, trigonally or linearly by P atoms, which are coordinated by nine metal atoms in the form of a tricapped trigonal prism. Therefore the atomic arrangement of Er₃Pd₇P₄ is related to the structures of ternary transition metal phosphides with a metal: phosphorus ratio of 2:1. Band calculations using the Extended Hückel method show strong covalent Pd? P bonds and weak bonding interactions between Pd atoms with Pd? Pd distances shorter than 2.9 Å.     

SYNTHESIS OF CROSS-CONJUGATED （p-PHENYLENE）S-POLY（p- PHENYLENEVINYLENE）S HYBRIDS WITH LOW CONTENT OF STRUCTURAL DEFECTS

The novel shish-kebab-type liquid crystalline cross-conjugated （p-phenylene）s-poly（p-phenylenevinylene）s hybrid was synthesized through Gilch polymerization. Their structures and properties were characterized by NMR, GPC, DSC, X-ray diffraction and polarizing optical microscope （POM）. ^1H-NMR investigation of the polymers indicates that the shish-kebab-structure has a strong ability to suppress the structural defects in the polymers. The polymers are enantiotropic liquid crystals. The melting point （Tm） of the polymers decreases when the length of the alkoxy tails of the mesogenic units increases. The mesophase was identified by X-ray diffraction method. They showed not only a smectic LC phase, but also a strong green fluorescence in chloroform. The maximum absorption band of the ＂kebabs＂ of the two, 5-bis（4＇- alkoxyphenyl）benzene at 280 nm did not appear in absorption spectra of the polymers. The same phenomena were also observed in the fluorescence spectra. These results imply that the polymers have formed a cross-conjugated uniform structure and achieved an extended n-conjugation polymer.     

PPV-PDMeOPV共聚物发光性质的实验和理论研究

具有优良电致发光性能的有机聚合物材料的研制及其发光性能和应用的研究是９０年代新兴的高科技领域．聚对苯乙炔［Ｐｏｌｙ（ｐ－ｐｈｅｎｙｌｅｎｅｖｉｎｙｌｅｎｅ）,缩写为ＰＰＶ,又称聚苯撑乙烯］是这一领域最先研制出来的具有代表性的材料［１,２］．为改变ＰＰ...     

含氮杂环并苯类高聚物结构与能带规律的从头算和半经验量子化学研究

采用从头算ＨＦ和半经验量子化学方法,对含氮杂环并苯类高聚物体系进行几何结构优化．比较不同方法下它们的电子性质的差异,揭示聚并苯、聚并吡啶、聚并吡嗪的能带分布特征和规律．为深入研究导电、发光等功能材料及能带匹配器件的分子设计提供依据．     

Synthesis and Infrared Multi‐band Absorption Properties of Core‐shell NaYF4:Yb3+, Er3+@SiO2 Nanoparticles

Due to the unique size effects, nanomaterials in infrared absorption have attracted much attention for their strong absorption in the infrared region. To achieve the infrared multi‐band absorption, we propose to synthesize a core‐shell structure nanomaterial consisting of NaYF₄:Yb³⁺, Er³⁺ core and a layer of SiO₂ as shell. A series of NaYF₄:Yb³⁺, Er³⁺ nanocrystals were synthesized through hydrothermal method by adjusting the ratio of citric acid(CA)‐to‐NaOH, and the effects of CA concentration, and NaOH concentration were studied in detail. NaYF₄:Yb³⁺, Er³⁺@SiO₂ nanoparticles were synthesized by sol‐gel method using TEOS as silica source. The results show that the core‐shell NaYF₄:Yb³⁺, Er³⁺@SiO₂ nanoparticles were successfully synthesized. Up‐conversion spectra of these nanoparticles were recorded with 980 nm laser excitation under room temperature. There are no changes of the emission centers of nanoparticles before or after silica coating, but the emission intensities of nanoparticles after silica coating are weakened. Furthermore, the property of infrared multi‐band absorption was tested through ultraviolet‐visible‐near infrared spectrophotometer and infrared absorption spectra. The results illustrate that the multi‐band infrared absorption nanomaterial was successfully synthesized.