Investigation of the ν1−2ν2 fermi diad of OF2 by means of IR-MW double resonance

The ν₁?2ν₂ Fermi diad of OF₂ at 928 cm^?1 was investigated by IR-MW double resonance using CO₂ and N₂O lasers. Using the data of Morino (ref. 1) and the additional rotational transitions measured in this work, a partial distortion analysis of the states (1,0,0)′ and (0,2,0)′ could be carried out. The accurately determined frequencies of five IR transitions in the ν′₁ band and of two in the ν′₂ band allowed the band centres to be calculated in both cases.     

Synthesis, crystal and band structures, and optical properties of a new supramolecular complex: [Hg6Sb4](InBr6)Br

A new supramolecular complex [Hg₆Sb₄](InBr₆)Br (1) has been prepared by the solid-state reaction of HgBr₂ with elemental In and Sb at 450 °C. The crystal structure of 1 features a three-dimensional [Hg₆Sb₄]⁴⁺ framework with cavities of two different sizes occupied by different kinds of guest anions. The bigger cavities are filled with the octahedral InBr₆³⁻ ions, while the smaller cavities trap Br⁻ ions. The optical properties were investigated in terms of the diffuse reflectance and infrared spectra. The electronic band structure along with density of states (DOS) calculated by DFT method indicates that the present compound is semiconductor, and the optical absorption is mainly originated from the charge transitions from Sb-5p and Br-4p to In-5s and Hg-6s states.     

Electronic Structure and Optical Properties of K2Ti6O13 Doped with Transition Metal Fe or Ag

Based on the experimental study of the optical properties of K₂Ti₆O₁₃ doped with Fe or Ag, their electronic structures and optical properties are studied by the first-principles method based on the density functional theory (DFT). The calculated optical properties are consistent with the experiment results. K₂Ti₆O₁₃ doped with substitutional Fe or Ag has isolated impurity bands mainly stemming from the hybridization by the Fe 3d states or Ag 4d states with Ti 3d states and O 2p states and the band gap becomes narrower, the absorption edge of K₂Ti₆O₁₃ thus has a clear red shift and the absorption of visible light can be realized after doping. For Fe-doped K₂Ti₆O₁₃, the impurity bands are in the middle of the band gap, suggesting that they can be used as a bridge for valence band electrons transition to the conduction band. For Ag-doped K₂Ti₆O₁₃, the impurity bands form a shallow acceptor above the valence band and can reduce the recombination rate of photoexcited carriers. The experimental and calculated results are significant for the development of K₂Ti₆O₁₃ materials that have absorption under visible light.     

Synthesis, crystal and band structures, and properties of a new supramolecular complex (Hg2As)2(CdI4)

A new quaternary supramolecular complex (Hg₂As)₂ (CdI₄) (1) has been prepared by the solid-state reaction and structurally characterized by single crystal X-ray diffraction analysis. Compound 1 crystallizes in the space group P2₁ of the monoclinic system with two formula units in a cell: a=7.945(4), b=12.934(6), c=8.094(4) Å, β=116.898°(1), V=741.7(6) Å³. The structure of 1 is characterized by a tridymite-like three-dimensional cationic framework, which is composed of mercury and arsenic atoms, with the channels being occupied by discrete CdI₄²⁻ tetrahedral guest-anions. The optical properties were investigated in terms of the diffuse reflectance and Fourier transform infrared spectra. The electronic band structure along with density of states (DOS) calculated by DFT method indicates that the present compound is a semiconductor with a direct band gap, and that the optical absorption is mainly originated from the charge transitions from I-5p and As-4p to Cd-5s and Hg-6s states.     

Crystal structure and energy band and optical properties of phosphate Sr3P4O13

A single crystal of the compound Sr₃P₄O₁₃ has been found and the crystal structure has been characterized by means of single crystal X-ray diffraction analysis. The compound crystallizes in triclinic system and belongs to space group . It builds up from SrO₇ polyhedra and P₄O₁₃⁻⁶ anions and has a layered structure, and the Sr atoms are located in the interlayer space. The absorption and luminescence spectrum of Sr₃P₄O₁₃ microcrystals have been measured. The calculated results of crystal energy band structure by the DFT show that the solid state of Sr₃P₄O₁₃ is an isolator with direct band gap. The calculated total and partial density of states indicate that the top valence bands are contributions from P 3p and O 2p states and low conduction bands mostly originate from Sr atomic states. The calculated optical response functions expect that the Sr₃P₄O₁₃ is a low refractive index, and it is possible that the Sr₃P₄O₁₃ is used to make transparent material between the UV and FR light zone.     

New interpretation of spectral and photochemical properties of [Fe(CN)5NO]2−

All known assignments of electronic transitions in the [Fe(CN)₅NO]^2? ion are inconsistent with the observed characteristics of absorption bands and with the most recent data on photoactivity. Results of more advanced calculations are presented, with Scaled INDO SCF calculations repeated for all excited states separately. In contrast to the older treatments it proves possible to explain why band I is inactive, why irradiation within the band II results in a pure exchange of NO⁺ and H₂O and why irradiation within the frequency range of band IV results in a redox reaction, followed by exchange of NO and H₂O.     

Synthesis, band structure, and optical properties of Ba2ZnV2O8

A novel compound Ba₂ZnV₂O₈ has been synthesized in high temperature solution reaction and its crystal structure has been characterized by means of single crystal X-ray diffraction analysis. It crystallizes in monoclinic system and belongs to space group P2₁/c with a=7.9050(16), b=16.149(3), , β=90.49(3). It builds up from 1-D branchy chains of [ZnV₂O₈⁴⁻]_∞, and the Ba²⁺ cations are located in the space among these chains. The IR spectrum, ultraviolet-visible diffuse reflection integral spectrum and fluorescent spectra of this compound have been investigated. The calculated results of energy band structure by the density functional theory method show that the solid-state compound of Ba₂ZnV₂O₈ is an insulator with direct band gap of 3.48 eV. The calculated total and partial density of states indicate that the top valence bands are contributions from the mixings of O-2p, V-3d, and Zn-3d states and low conduction bands mostly originate from unoccupied antibonding states between the V-3d and O-2p states. The V-O bonds are mostly covalence characters and Zn-O bonds are mostly ionic interactions, and the ionic interaction strength is stronger between the Ba-O than between the Zn-O. The refractive index of n_x, n_y, and n_z is estimated to be 1.7453, 1.7469, and 1.7126, respectively, at wavelength of 1060 nm for Ba₂ZnV₂O₈ crystal.     

Emission spectra of Cs2NaTbCl6 and Cs2NaYCl6: Tb3+

The emission spectra of microcrystalline Cs₂NaTbCl₆ and Cs₂Na(Y_0.99Tb_0.01)Cl₆ have been measured at room temperature and at 77 K. The crystal structures of these compounds are face-centered cubic and the terbium (III) ions lie at sites of octahedral (O_h) symmetry surrounded by six chloride ions. Emission is observed from both the ⁵D₃ and ⁵D₄ excited states of Tb³⁺. Assignments have been made for nearly all of the magnetic-dipole transitions split out of the Tb³⁺⁷F₆, ⁷F₅, ⁷F₄, ⁷F₃, ⁷F₂, ⁷F₁ ← ⁵D₄ and ⁷F₄, ⁷F₂ ← ⁵D₃ transitions. These assignments are based on the calculated transition energies and relative magnetic-dipole strengths and intensities obtained from a weak-field crystal-field analysis of octahedral TbCl₆^3? units. Magnetic-dipole lines dominate the spectra for transitions of ΔJ = ±1 free-ion parentage, whereas both magnetic-dipole lines and vibronically induced electric-dipole lines contribute significantly to the emission intensities of the ΔJ = 0, ±2 transitions. The crystal-field sub-levels of both ⁵D₃ and ⁵D₄ appear to reach a Boltzmann thermal equilibrium prior to emission. Emission from ⁵D₃ is partially quenched in going from low temperature to high temperature and in going from Cs₂NaYCl₆: Tb³⁺ (1%) to Cs₂NaTbCl₆.This study has led to the identification and assignment of nearly all of the pure magnetic-dipole transitions split out of the Tb³⁺⁷F₆, ⁷F₅, ⁷F₄, ⁷F₃, ⁷F₂, ⁷F₁ ← ⁵D₄ and ⁷F₄, ⁷F₂ ← ⁵D₃ transitions in crystal-line Cs₂NaTbCl₆. The assignments were based on calculated transition energies and relative magnetic-dipole strengths (and intensities) obtained from a (weak-field) crystal-field analysis of octahedral (O_h) TbCl₆^3? clusters. Excellent agreement between the calculated and observed relative intensities of the magnetic-dipole lines was achieved by assuming a Boltzmann equilibrated set of crystal-field sub-levels for both the ⁵D₄ and ⁵D₃ emitting states. Furthermore, the experimental results suggest that ⁵D₄ ← ⁵D₃ relaxation is temperature-dependent.The energy levels calculated and displayed in table 1 appear to be qualitatively correct and are in semiquantitative agreement with the emission results (as interpreted in section 4). Calculated and observed transition energies for the assigned magnetic-dipole transitions generally agree to within 0.2%.One of the most remarkable features of the emission spectra obtained on Cs₂NaTbCl₆ is the absence of any vibrational structure in the ΔJ = ± 1 transitions (⁷F₆, ⁷F₃ ← ⁵D₄ and ⁷F₄, ⁷F₂ ← ⁵D₃), and the presence of extensive vibrational structure in the ΔJ = O, ±2 transitions (⁷F₆, ⁷F₄, ⁷F₂ ← ⁵D₄). If other than OO vibronic transitions do contribute to the ΔJ = ±1 emissions, their intensities must be at least two or three orders-of-magnitude weaker than the OO magnetic-dipole lines. Vibronically induced electric-dipole transitions appear, however, to make substantial contributions to the ⁷F₆, ⁷F₄, ⁷F₂ ← ⁵D₄ emission spectra. A clear-cut theoretical explanation for the absence of vibrational structure in the ΔJ = ±1 transitions is not readily apparent. We are presently examining this problem in greater detail.     

Ab-initio calculation of structural, electronic, and optical characterizations of the intermetallic trialuminides ScAl3 compound

We present first-principles study of the electronic and the optical properties for the intermetallic trialuminides ScAl₃ compound using the full-potential linear augmented plane wave method within density-functional theory. We have employed the generalized gradient approximation (GGA), which is based on exchange-correlation energy optimization to calculate the total energy. Also we have used the Engel-Vosko GGA formalism, which optimizes the corresponding potential for calculating the electronic band structure and optical properties. The electronic specific heat coefficient (γ), which is a function of density of states, can be calculated from the density of states at Fermi energy N(E_F). The N(E_F) of the phase L1₂ is found to be lower than that of D0₂₂ structure which confirms the stability of L1₂ structure. We found that the dispersion of the band structure of D0₂₂ is denser than L1₂ phase. The linear optical properties were calculated. The evaluations are based on calculations of the energy band structure.     

Dipole moment for the v2 = 1 vibrational state of 15NH3 by saturation laser stark spectroscopy

An intracavity Stark cell was used to observe inverse Lamb dips of five transitions of the ¹⁵NH₃v₂ band, saturated by CO₂ laser lines. Accurate values of the electric dipole moment of v₂ = 1, (J,K) = (4,4); (7,7); (8,8) and (11,9) states and of the (J,K) = (5,3) vibrational ground state have been obtained.     

Low-temperature absorption spectra of the MoO2−4 ion in Cs2SO4 and of the ReO−4 ion in RbClO4 and in (C2H5)4NClO4

Absorption spectra of single crystals of Cs₂SO₄ doped with MoO^2?₄ and of RbClO₄ and (C₂H₅)₄HClO₄ doped with ReO^?₄ have been measured at the liquid-helium temperature. All spectra show two band systems with pronounced vibrational structures. In T_d symmetry they must correspond to ¹T₂ - ¹A₁ charge-transfer electornic transitions. It is likely that in the two band systems there are more than two electronic transitions.     

The reflectivity spectra of ZnXP2 (X=Si, Ge, and Sn) compounds

Full Potential Augmented Plane Wave plus local orbital method ( FAPW+lo) calculations were performed for ZnSiP₂, ZnGeP₂, and ZnSnP₂ in the chalcopyrite structure in order to investigate the optical properties and to show the origin of the different optical transitions and their correspondence in the band structure. It is found that the most important features of the band gap is pseudo-direct for ZnSiP₂, indirect for ZnGeP₂, and direct for ZnSnP₂. Then the contribution of the different transitions peaks are analyzed from the imaginary part of the dielectric function and the reflectivity spectra.     

Electron microscopy, spectroscopy, and first-principles calculations of Cs2O

Oxides of cesium play a key role in ameliorating the photoelectron emission of various opto-electronic devices. However, due to their extreme reactivity, their electronic and optical properties have hardly been touched upon. With the objective of better understanding the electronic and optical properties of Cs₂O in relationship to its structure, an experimental and theoretical study of this compound was undertaken. First-principles density functional theory calculations were performed. The preferred structural motif for this compound was found to be anti-CdCl₂. Here three Cs-O-Cs molecular layers are stacked together through relatively weak van-der-Waals forces. The energy bands were also calculated. The lowest transition at 1.45 eV, was found to be between the K point in the valence band to the Γ point in the conduction band. A direct transition at 2 eV was found in the center (Γ) of the Brillouin zone. X-ray powder diffraction, transmission electron microscopy and selected area electron diffraction were used to analyze the synthesized material. These measurements showed good agreement with the calculated structure of this compound. Absorption measurements at 4.2 K indicated two optical transitions with somewhat higher energy (indirect one at 1.65 and a direct transition at 2.2 eV, respectively). Photoluminescence measurements also showed similar transitions, suggesting that the lower indirect transition is enhanced by three nearby minima at 1.5 eV in the Brillouin zone.     

The Family of Ln2Ti2S2O5 Compounds (Ln=Nd, Sm, Gd, Tb, Dy, Ho, Er, and Y): Optical Properties

The optical properties of Ln₂Ti₂S₂O₅ compounds (Ln=Nd, Sm, Gd, Tb, Dy, Ho, Er, and Y) have been measured. Diffuse reflectance spectra revealed a strong absorption band above 2 eV, which explains the color of the compounds. Moreover, other bands, with a lower intensity, have been attributed to 4f-4f rare earth transitions. In the case of neodymium the derived energy level scheme is rich enough to determinate a set of phenomenological crystal field parameters that correctly reproduce the spectrum. These parameters were also calculated from the crystallographic structure, in a good agreement with the experiment. Finally, the paramagnetic susceptibility, well reproduced by the calculation, confirms that the rare earth is in a trivalent state.     

AB initio calculation of vertical transition energies of the C2H2 molecule

Various ab initio SCF and Cl treatments are reported for the acetylene molecule in ground and excited states at its fixed linear equilibrium geometry. The results speak in favor of the former analysis of the vacuum UV absorption spectra of C₂H₂ given by Wilkinson according to which above the X?C state an allowed transition to a linear upper state (X?D) and two allowed transitions with broad bands (X?E and X?F) to non-linear upper states are present. The calculated order and spacing of the excited states does not support the new analysis given by Jungen according to which only one allowed transition (X?F) and a forbidden one to a linear upper state (X?D) should appear between 1250 and 1360 A.     

Electronic structure and photoluminescence properties of Eu-activated Ca2BN2F

The electronic structure of undoped and luminescence properties of Eu²⁺-doped Ca₂BN₂F have been investigated. First-principles calculations for Ca₂BN₂F show that the valence band is mainly composed of F and N 2p, B 2s and 2p orbitals, while the Ca 4s and 3d are almost empty, indicating that Ca₂BN₂F is a very ionic compound. The valence band close to the Fermi level is dominated by the N 2p states, and the bottom of the conduction band is determined by the Ca 3d and N/B 3s orbitals. The direct energy gap is calculated to be about 3.1 eV, in fair agreement with the experimental data of ∼3.6 eV derived from the diffuse reflection spectrum. Due to the high degree of ionic bonding of the coordinations of Eu with (N, F) on the Ca sites, Ca₂BN₂F:Eu²⁺ shows strong blue emission with a maximum at about 420 nm upon UV excitation in the absorption range of 330-400 nm.     

Band structure calculations on the monoclinic bulk and nano-SrAl2O4 crystals

The electronic structure of SrAl₂O₄ is calculated by density functional method and exchange and correlation have been treated by the generalized gradient approximation within the scheme due to Perdew-Burke-Ernzerhof. The bond length and bond covalency are also calculated by chemical bond method. Compared with the SrAl₂O₄ bulk crystal, the bond covalency of nanocrystal has an increasing trend; its band gap also is wider; the bond lengths of SrAl₂O₄ nanocrystal become shorter, which is responsible for the change of the covalency and band gap.     

b 1Σ+ emissions from group V-VII diatomic molecules: bo+ → X10+, X21 emissions of SbBr

Chemiluminescence studies of the reactions of microwave-discharged oxygen with SbBr₃ have led to the observation of some band sequences in the near infrared region which are attributed to b0⁺ → X₁0⁺ and b0⁺ → X₂1 transitions of SbBr. Analysis of the spectra yielded T_e values for the X₂1 and b0⁺ states of 874 ± 10 and 12756 ± 10 cm^?1, respectively, and vibrational frequencies in the X₁0⁺, X₂1 and b0⁺ states of ω′'_e(X₁, X₂) = 257 ± 10 and ω′_e(b) = 270 ± 10cm^?1.     

The ν3 and ν6 infrared bands of 12CD3F: An example of an α resonance

An example is given of an α resonance between A₁ and E vibrations of a symmetric top. This leads to a complicated pattern for the K structure of the ν₃ band of CD₃F and to the appearance of “perturbation-allowed” transitions. bl     

分子基磁体Cr[N(CN)2]2电子结构和半金属性的第一性原理研究

The electronic structure and half-metallicity of molecule-based ferromagnet Cr[N(CN)₂]₂ have been investigated using first-principles with generalized gradient approximation. The total energy, spin-polarized electronic band structure, density of states (DOSs) and spin mag-netic moments were all calculated. The calculations reveal that the compound Cr[N(CN)₂]₂ is a really half-metallic ferromagnet with a integral magnetic moment of 2.0000 μB per molecule in the optimized lattice constant. Based on the spin distribution and the DOS, it is found that the total magnetic moment is mainly from the Cr²⁺ with relative small contribution from C and N atoms. The sensitivity of the half-metallicity to small change in lattice constant is also discussed.