Experimental Band Research Articles

Vibrational and electronic properties of Na2Ti6O13

AbstractSodium hexatitanate, Na2Ti6O13, in the form of elongated microcrystals, were synthesized by solid‐state reaction of titanium dioxide and sodium carbonate. The monoclinic structure was confirmed by X‐ray powder diffraction and selected area electron diffraction. Electron diffraction was used to determined zone axis and the crystal‐grown direction, which allowed to perform polarized Raman measurements. Energy band gap and the electronic transition were studied by UV–Vis diffuse reflectance and using Tauc relation. Density functional theory (DFT) calculations also revealed an indirect allowed bandgap transition and a good agreement between theoretical and experimental energy band gaps were demonstrated. For the first time, the assignment of the vibrational modes was carried out in the samples and thoroughly compared with theoretical data obtained from DFT calculations. The most relevant of the 60 predicted optical phonon modes of Na2Ti6O13 were experimentally observed and assigned to their symmetries.

First principles study on electronic, magnetic and optical properties of Gd2NiMnO6

The double perovskite oxide materials have various applications in light absorber, solid oxide fuel cells, electrode materials for electrochemical energy devices, solid state thermoelectric devices, etc. The calculations of electronic, optical and magnetic properties of Gd2NiMnO6 (GNMO) double perovskite are aimed in the present work. GNMO crystallizes in monoclinic structure with P21/n (14) space group. Implementing first principles density functional theory, we have reported the spin-polarised electronic band structure, density of states (DOS), optical absorption property and magnetic moment of GNMO double perovskite. Furthermore, the effect of on-site d-d Coulomb interaction energy (Ueff) on the electronic and optical properties were investigated by applying a range of Hubbard parameters from 0 to 6 eV on Ni-3d and Mn-3d orbitals within the local spin density approximation (LSDA) and generalised gradient approximation (GGA). Interestingly, on applying Ueff in this range, band gap of GNMO enhanced progressively in both majority and minority spins and also for Ueff = 4 and 6 eV implemented on Ni-3d and Mn-3d orbits, respectively, we observe the band gap value 1.16 and 2.12 eV for the spin-up and spin-down states which is in good agreement with the previously reported experimental band gap value (1.5 eV). In this regard, the electronic structure and light absorption of GNMO have been analysed for Ueff = 4 and 6 eV implemented on Ni-3d and Mn-3d orbits, respectively. The calculations revealed suitable narrow band gap and large visible light absorption coefficient in GNMO, which are extremely desired for the high photovoltaic performance.

Preparation of novel KAlSiO4: Ce3+ broadband cyan-emitting phosphors via partial cation substitution for applications in white-light LEDs

Broadband cyan-emitting phosphors with strong absorption between 300 and 400 nm are ideal replacements for traditional blue and green phosphors used in commercial light-emitting diodes (LEDs). In this paper, a series of K1-xAlSiO4: xCe3+(x = 0.02–0.06) broadband cyan phosphors were prepared using the traditional high-temperature solid state method and the cation un-equivalent substitution strategy. It was found that the KAlSiO4 matrix has a monoclinic structure with high symmetry. The experimental and theoretical optical band gaps of the host were 5.6 eV and 4.86 eV, respectively. After doping with Ce3+, strong absorption was observed in the near ultraviolet region. The optimum Ce3+ doping concentration in the host was 0.04 as indicated by the strongest observed emission intensity. The full width at half maximum of the emission spectra of the series of samples are all greater than 120 nm and covered the blue and green wavelength ranges (370–600 nm). The luminous intensity of the K0·96AlSiO4: 0.04Ce3+phosphor at 150 °C was 91.1% of that at room temperature, and the Gaussian peak of the emission spectrum slightly broadened. These results were also combination with theoretical DFT calculations. It was found that the phosphor had very good thermal stability and rigidity. The phosphor was also mixed with a commercial red phosphor, interfaced with a UV chip and packaged into an LED. This LED was characterized and had a color rendering index greater than 90 across a broad range of drive currents. This work highlights the utility of the fabricated phosphor as means of simplifying white-light LED fabrication.

Raman- and Infrared-Active Phonons in Nonlinear Semiconductor AgGaGeS4

AgGaGeS4 is an emerging material with promising nonlinear properties in the near- and mid-infrared spectral ranges. Here, the experimental phonon spectra of AgGaGeS4 single crystals synthesized by a modified Bridgman method are presented. The infrared absorption spectra are reported. They are obtained from the fitting of reflectivity to a model dielectric function comprising a series of harmonic phonon oscillators. In the Raman spectra, several modes are registered, which were not detected in previous works. The analysis of the experimental vibrational bands is performed on the basis of a comparison with reported data on structurally related binary, ternary, and quaternary metal chalcogenides. The temperature dependence of the Raman spectra between room temperature and 15 K is also investigated.

A New Non-linear Stilbazolium Derivative Crystal of 4-[2-(3 Methoxy-phenyl)-vinyl]-1-methyl-pyridinium+ Iodide− (MMPI): Analysis of Its Structural, Surface, Optical and NLO Properties

New organic stilbazolium family of 4-[2-(3 methoxy-phenyl)-vinyl]-1-methyl-pyridinium+ iodide− (MMPI) was successfully synthesized using the condensation reaction method. The recrystallization process was carried out to improve the purity of the synthesized material, and MMPI and grown into a single crystal by the solvent evaporation method. The solubility of the (MMPI) material was taken at different temperatures with a mixture of solvent Methanol: Acetonitrile (1:1). The grown MMPI crystal structure and cell parameters were solved via single crystal X-ray diffraction analysis. The structural formation of the title material was also confirmed by Nuclear Magnetic Resonance spectroscopic (NMR) studies. The experimental vibrational bands in the synthesized material have been assigned by Fourier Transform Infrared (FT-IR) spectrum analysis. From the optical analysis, the grown crystal’s lower cut-off wavelength, transmittance range, and optical band gap were calculated. Chemical etching analysis was carried out on the grown crystal surface (MMPI) to study the surface property of the grown MMPI crystal. Along with etching, atomic force microscope (AFM) and scanning electron microscope (SEM) were also used to analyses the grown MMPI crystal surface. Hirshfeld surface analysis was used to analyses the intermolecular interactions. HOMO and LUMO energies were calculated theoretically using the Gaussian View 6 programmer. The chemical activity was evaluated via the molecular electrostatic potential using the density functional theory (DFT) method. The third-order nonlinear optical parameters of the title crystal were evaluated at He-Ne laser (632.8 nm) source with the single beam Z-scan technique. In addition, it shows significant reverse saturable absorption and self-defocusing.

Bioacoustics as Forms of Resistance: Growing Mycelium Instruments and Mushroom Communication in a High-Tech City-State

Singapore-based experimental band The Observatory (天文台樂團) recently showcased their bio-sonification exhibition at Singapore Art Museum: REFUSE (14 January–17 April 2022). Set against imagery of manicured gardens in a celebration of organic growth and decomposition, REFUSE is a critical pun. First, REFUSE means to reject the current anthropocentric worldview in a time of ecological crises, and secondly it embraces inter-media arts that fuse recycled instruments with bio-sounds. Instruments were either the platform to grow mushrooms onto, or even themselves fully bio-fabricated by mushrooms – including a fully playable lap steel mycelium guitar that is simultaneously played by a mushroom. To amaze the audience further, these instruments were all wired to vibrate, their rhythms controlled by a growing mycelium whose organic growth is visually mapped and translated into signals that trigger the vibration. As the humidity and density of the mushroom jar changes, the sounds also vary, each sound unique even during the same day. As Obervatory band-member Yuen Chee Wai (袁志偉) told En-Chieh Chiao of our cover-image curating team when describing the mycelium's sounds, “They play like a decomposing composition.” The cover team chose this exhibition because it speaks to a research note and to an article in this issue that respectively address the issue of noise control and aging in Singapore. While the city–state endeavors to contain both noise and health in old age as parts of governance, here the artists renounce control over sound and let biological non-human actors set the course of subtle sensory experiences.

New polymorphic phase of arachidic acid crystal: structure, intermolecular interactions, low-temperature stability and Raman spectroscopy combined with DFT calculations.

Saturated monocarboxylic fatty acids with long carbon chains are organic compounds widely used in several applied fields, such as energy production, thermal energy storage, antibactericidal, antimicrobial, among others. In this research, a new polymorphic phase of arachidic acid (AA) crystal was synthesized and its structural and vibrational properties were studied by single-crystal X-ray diffraction (XRD) and polarized Raman scattering. The new structure of AA was solved at two different temperature conditions (100 and 300 K). XRD analysis indicated that this polymorph belongs to the monoclinic space group P21/c (C2h5), with four molecules per unit cell (Z = 4). All molecules in the crystal lattice adopt a gauche configuration, exhibiting a R22(8) hydrogen bond pattern. Consequently, this new polymorphic phase, labeled as B form, is a polytype belonging to the monoclinic symmetry, i.e., Bm form. Complementarily, Hirshfeld's surfaces were employed to analyze the intermolecular interactions within the crystal lattice of this polymorph at temperatures of 100 and 300 K. Additionally, density functional theory (DFT) calculations were performed to assign all intramolecular vibration modes related to experimental Raman-active bands, which were properly calculated using a dimer model, considering a pair of AA molecules in the gauche configuration, according to the solved-crystal structure.

Effects of solvent vapor annealing on the optical properties and surface adhesion of conjugated D : A thin films.

A diketopyrrolopyrrole (DPP) and perylene diimide (PDI)-based molecule, denoted as PDI-DPP-PDI, was investigated as an electron acceptor material in bulk heterojunction (BHJ) solar cells, with poly[[4,8-bis [5-(2-ethylhexyl)-2-thienyl]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl] [2-(2-ethyl-1-oxohexyl)thieno[3,4-b]thiophenediyl]] (PBDTTT-CT) as an electron donor. The donor polymer and the acceptor molecule have complementary absorption spectra, which is an essential feature for energy collection in organic solar cells. However, AFM images indicated the presence of isolated and microsized PDI-DPP-PDI domains along the surface of the films, which reduced the power conversion efficiency. Therefore, to improve the homogenization of the acceptor along the film, a post-deposition treatment, denoted as solvent vapor annealing (SVA), was performed in a saturated atmosphere containing the vapour of an organic solvent for 3-10 minutes. This procedure changed the optical and morphological properties of the PBDTTT-CT : PDI-DPP-PDI active layer, resulting in increased power conversion efficiency values by more than 2.5 times (reaching 5.1%). Theoretical simulation pointed out that the experimental absorbance band localized at 580 nm, which appeared after SVA treatment, is possibly related to an intense simulated band with a maximum at 572 nm, resulting from a pair of transitions starting in the copolymer and ending in PDI-DPP-PDI, in regions where both are stacked at about 3 Å. The most significant natural transition orbitals (NTOs) related to these transitions indicated charge transfer character. Moreover, analyses carried out by power spectrum density (PDS) of images acquired from the SVA-treated film indicated that in the region of larger frequencies, across the length scale at around 30-70 nm, an additional fractal region appeared with a Ds of 0.95, indicating a flattened region, possibly related to changes in the overall conformation after SVA treatment. This indicates an improvement in the molecular packing, a feature not observed in the as-cast film. The analyses by force curve spectroscopy pointed out increased adhesion forces and adhesion energy in the PBDTTT-CT : PDI-DPP-PDI film after SVA treatment; this feature enhanced the interfacial interaction with the top electrodes, reflecting improved charge extraction in the photovoltaic device.

A study on pseudo-potential effect, electronic structure, aquatic toxicity, and optical properties of perovskites solar cell of Cs2NiCl6, Cs2NiBr6, and Cs2PtBr6: Through DFT methods

The main impediment to practical application is the toxicity of lead ions in halide perovskite absorbing materials. Computing tools based on density functional theory (DFT) were used to predict the intrinsic properties of potential for double perovskites to be effective and suitable for optoelectronic applications, replacing the conventional lead halide perovskites with environmentally friendly elements. The Generalized Gradient Approximation (GGA) with Perdew-Burke-Ernzerhof (PBE) functional was used to screen homovalent alternatives for B and X-site ions in vacancy-ordered double perovskite Cs2BX6 (B=Pt, Ni, X= Cl, Br) for solar cell applications. Using the GGA with PBE functional, the band gap was calculated to be 1.411 eV, 0.482 eV, and 0.378 eV for the Cs2PtBr6, Cs2NiCl6, and Cs2NiBr6, respectively. The experimental band gap value of mother crystal's (Cs2PtBr6) was at 1.42 eV. Next, the DOS, PDOS and optical properties were computed using GGA with PBE functional. Then, the local density approximation (LDA) with Ceperley and Alder with Perdew and Zunger (CA-PZ) was executed to compare the GGA with PBE for electronic band structure. In addition, the OTFG ultra soft, OTFG norm conserving, ultra soft and norm conserving methods of pseudopotential were used for both GGA with PBE and LDA with CA-PZ to make and ensure the right or accurate DFT functional for those crystals. At last, the optical properties and their toxicity have been evaluated for their rational design of potential double perovskite materials with improved optoelectronic properties.

Crystal structure, phase width, and physical properties of the barium tetrel selenides Ba6Si2-xGexSe12 (x = 0, 0.5, 1, and 1.5) with ultralow thermal conductivity.

The new compound Ba6Si2Se12 was synthesized, and the crystal structure and physical properties are reported here. Ba6Si2Se12 adopts a new structure type in the triclinic P1̄ space group with the lattice parameters a = 9.1822(7) Å, b = 12.2633(14) Å, c = 12.3636(18) Å, α = 109.277(3)°, β = 104.734(2)°, and γ = 100.4067(16)°. Notably, the structure features disordered Se22- dumbbells that have also been observed in the germanium selenide with the analogous stoichiometry (Ba6Ge2Se12). Density functional theory calculations revealed that Ba6Si2Se12 is a semiconductor with a calculated band gap of 1.74 eV. UV/vis/NIR absorption spectra indicated that the experimental band gap of Ba6Si2Se12 is 1.89 eV. While exploring this compound's phase width, it was discovered that up to 75% of the Si could be substituted with Ge while retaining the structure type. Rietveld refinements were performed on the phase-pure samples of Ba6Si2-xGexSe12 (x = 0, 0.5, 1, and 1.5) using data collected at the Canadian Light Source's High Energy Wiggler Beamline. The cell parameters, Si/Ge occupancies, and disordered Se22- occupancies were studied. Raman spectra displayed the expected Si-Se and Ge-Se stretching modes from 215 cm-1 to 280 cm-1. The samples were also hot-pressed into pellets to determine their thermal conductivity values ranging from 0.5 to 0.4 W m-1 K-1 for the x = 0, 0.5, and 1.5 samples. The x = 1 sample stood out with a remarkably low thermal conductivity of 0.3 W m-1 K-1, consistent from room temperature up to 573 K.

Synthesis, structure and characterization of Cd2TeO3Cl2 with unprecedented [Cd2O6Cl4] octahedral dimers.

A new mixed anionic compound Cd2TeO3Cl2 with unprecedented [Cd2O6Cl4] octahedral dimers has been synthesized, and millimeter-scale single crystals of Cd2TeO3Cl2 have been grown by the vertical Bridgman method with CdCl2 as the flux. Cd2TeO3Cl2 crystallizes in the centrosymmetric P1̄ (no. 2) space group, and shows a mixed cationic layer structure constituted by distorted [TeO3] motifs, mixed anionic [Cd2O6Cl4] chains, and [Cd2O6Cl4] octahedral dimers. Experimental and theoretical results show that Cd2TeO3Cl2 is a direct band gap compound with an experimental band gap of ∼4.25 eV. Meanwhile, the compound has good optical transmittance in the 3-5 μm atmospheric window. The results indicate that Cd2TeO3Cl2 could be used as a promising mid-IR window material, and could enrich the chemical and structural diversity of oxides.

Clarifying the effects of nanoscale porosity of silicon on the bandgap and alignment: a combined molecular dynamics-density functional tight binding computational study.

Porous silicon (pSi) has been studied for its applications in solar cells, in particular in silicon-silicon tandem solar cells. It is commonly believed that porosity leads to an expansion of the bandgap due to nano-confinement. Direct confirmation of this proposition has been elusive, as experimental band edge quantification is subject to uncertainties and effects of impurities, while electronic structure calculations on relevant length scales are still outstanding. Passivation of pSi is another factor affecting the band structure. We present a combined force field-density functional tight binding study of the effects of porosity of silicon on its band structure. We thus perform electron structure-level calculations for the first time on length scales (several nm) that are relevant to real pSi, and consider multiple nanoscale geometries (pores, pillars, and craters) with key geometrical features and sizes of real porous Si. We consider the presence of a bulk-like base with a nanostructured top layer. We show that the bandgap expansion is not correlated with the pore size but with the size of the Si framework. Significant band expansion would require features of silicon (as opposed to pore sizes) to be as small as 1 nm, while the nanosizing of pores does not induce gap expansion. We observe a graded junction-like behavior of the band gap as a function of Si feature sizes as one moves from the bulk-like base to the nanoporous top layer.

Synthetic pathway of 2-fluoro-N,N-diphenylbenzamide with opto-electrical properties: NMR, FT-IR, UV-Vis spectroscopic, and DFT computational studies of the first-order nonlinear optical organic single crystal

Abstract 2-Fluoro-N,N-diphenylbenzamide (2FNNDPBA), a natural nonlinear optical (NLO) single crystal, was incorporated from diphenylamine utilizing 2-fluoro benzoyl chloride as a side chain. The single crystals were successfully developed by a slothful evaporation arrangement approach utilizing ethyl acetate as a dissolvable solvent at room temperature. The synthesized compound fragmented ion peak (m/z = 291) was affirmed by gas-chromatographic mass spectrometry investigation. The unit cell dimensions were assessed using single-crystal X-ray diffraction analysis, which reveals that the crystals possess the orthorhombic system with space group Pbca. The existence of proton and carbon in a compound was affirmed by 1H and 13C nuclear magnetic resonance. The functional groups therein of 2FNNDPBA have been identified from FT-IR and FT-Raman studies and amide carbonyl stretching frequency peak appeared at 1,662 cm−1. The lower cut-off wavelength of 2FNNDPBA is found to be 240 nm and the experimental and theoretical optical band gap was calculated as 3.21 and 3.1083 eV. The UV-Visible spectrum of 2FNNDPBA shows two high-flying peaks at 240 and 273 nm. Major weight losses were observed between 160°C and 275°C for the designated compound. The thermal property for 2FNNDPBA was estimated by thermogravimetric analysis/differential thermal analysis investigation, which shows immense thermal strength up to 171°C. Density functional theory method with Gaussian 09 software for theoretical investigations of 2FNNDPBA for Mulliken charge analysis, highest occupied molecular orbital–lowest-lying unoccupied molecular orbital, and molecular electrostatic potential properties has been analyzed. The SHG productivity was proved by Kurtz-Perry powder strategy and has an efficiency 2.22 times that of standard potassium dihydrogen phosphate. The laser damage threshold of 2FNNDPBA crystals was discovered to be 1.18 GW·cm−2. The hyperpolarizability simulations further show that the current material has an excellent NLO activity tendency. The melting point of the developed crystal is 158°C.

A Study on the Luminescent Terbium(III) and Pyridine 2,6 Dicarboxylate Complexes by Experimental and TD-DFT Approaches.

Tb3+ luminescence is enhanced by complex formation in aqueous phases as its pyridine 2,6 dicarboxylate (dpa2-) complexes by using experimental spectroscopic techniques and theoretical time-dependent density functional theory (TD-DFT) calculations. The fluorimetric titration of Tb3+ ion with dpa2- ion is followed at λext/λems = 310/490 nm and 310/545 nm, the emission intensities of which are graphed against the mol ratios of the ligand to metal ion [moles of dpa2-/mol of Tb3+]. Experimental results denote that the tris complex; [Tb(dpa)3]3- is the most stable form at pH > 5.3. Molecular absorption spectra of tris complex shows a batho-chromic shift of 222nm of dpa2- band to 232nm accompanied by the hyper-chromic effect at 272nm band. The luminescence intensities at 490, 545, 592 and 620nm are enhanced over 100 times in tris complex. The coordination of complexes calculated by thermodynamic cycles and with supporting the experimental result, the most stable form was found to be nine coordinated tris complex; [Tb(dpa)]3-. The theoretical TD-DFT calculations perfectly matched the experimental absorption and emission bands of tris-complex. The novelty of this study is to present the first theoretical calculation of the phosphorescence results and energy transfer process for emission path of Tb3+ and pda2- aqua complexes.

Unraveling the Photoelectron Spectrum of 1-Phospha-2,3,4-triazolate Anion, HCPN3–, A Theoretical Approach

The first five low-lying electronic states of HCPN3 are probed through extensive ab initio electronic structure and quantum dynamics studies to reproduce the 193 nm photoelectron spectrum. Vibronic Hamiltonian is constructed and availed for time-dependent (TD) and time-independent (TI) quantum dynamical studies. The presence of numerous conical intersections (CIs) and crossings among electronic states yielded interesting nonadiabatic effects in the photoelectron bands of the overall spectrum. Moreover, the theoretical bands corresponding to five electronic states have reproduced all three experimental spectral bands. Among these, the first two bands originated due to a combination of four electronic states as predicted by previous studies. The third band corresponds to the fifth electronic state. The results calculated via TD and TI approaches exhibited satisfying agreement with the experimental results.

Efficient Removal of High-Concentration Dye Pollutants in Wastewater Using Composite Photocatalyst NH2-MIL-125 (Ti)/g-C3N4 Nanosheets Under Visible Light

The NH2-MIL-125(Ti)/g-C3N4 nanosheets composite photocatalyst was prepared by one-step solvothermal synthesis and used to remove high-concentration dye wastewater. The morphology, structure, and photoelectrochemical properties of the as-synthesized samples were characterized by XRD, SEM, XPS, FT-IR, UV–vis DRS PL, EIS, and transient photocurrent. The results showed that g-C3N4 nanosheets were tightly loaded on the surface of NH2-MIL-125(Ti) to form the NH2-MIL-125(Ti)/g-C3N4 nanosheets composite photocatalyst. Among them, NM (Ti)/CNNS30 showed the best adsorption performance and photocatalytic degradation activity for removing high-concentration RhB solution. In addition, the optimal experimental conditions were also explored, such as the concentration of RhB solution, the dosage of NM (Ti)/CNNS30, and the initial pH of RhB. Finally, the mechanism of photocatalytic degradation of NM(Ti)/CNNS30 on high-concentration RhB solution was also proposed based on active species capture experiment and energy band structure analysis. It was inferred that O2− and h+ were the main active species for NM(Ti) photocatalytic degradation of high-concentration RhB. This work provided new insights into the design and synthesis of highly efficient photocatalysts for the practical treatment of high-concentration dye wastewater.

Infrared Spectra and Phototransformations of meta-Fluorophenol Isolated in Argon and Nitrogen Matrices

Monomers of meta-fluorophenol (mFP) were trapped from the gas phase into cryogenic argon and nitrogen matrices. The estimated relative energies of the two conformers are very close, and in the gas phase they have nearly equal populations. Due to the similarity of their structures (they only differ in the orientation of the OH group), the two conformers have also similar predicted vibrational signatures, which makes the vibrational characterization of the individual rotamers challenging. In the present work, it has been established that in an argon matrix only the most stable trans conformer of mFP exists (the OH group pointing away from the fluorine atom). On the other hand, the IR spectrum of mFP in a nitrogen matrix testifies to the simultaneous presence in this matrix of both the trans conformer and of the higher-energy cis conformer (the OH group pointing toward the fluorine atom), which is stabilized by interaction with the matrix gas host. We found that the exposition of the cryogenic N2 matrix to the Globar source of the infrared spectrometer affects the conformational populations. By collecting experimental spectra, either in the full mid-infrared range or only in the range below 2200 cm-1, we were able to reliably distinguish two sets of experimental bands originating from individual conformers. A comparison of the two sets of experimental bands with computed infrared spectra of the conformers allowed, for the first time, the unequivocal vibrational identification of each of them. The joint implementation of computational vibrational spectroscopy and matrix-isolation infrared spectroscopy proved to be a very accurate method of structural analysis. Some mechanistic insights into conformational isomerism (the quantum tunneling of hydrogen atom and vibrationally-induced conformational transformations) have been addressed. Finally, we also subjected matrix-isolated mFP to irradiations with UV light, and the phototransformations observed in these experiments are also described.

Enhanced energy deposition and carrier generation in silicon induced by two-color intense femtosecond laser pulses

We theoretically investigate the optical energy absorption of crystalline silicon subject to dual-color femtosecond laser pulses, using the time-dependent density functional theory (TDDFT). We employ the modified Becke-Johnson (mBJ) exchange-correlation potential which reproduces the experimental direct bandgap energy $E_g$. We consider situations where the one color is in the ultraviolet (UV) range above $E_g$ and the other in the infrared (IR) range below it. The energy deposition is examined as a function of mixing ratio $\eta$ of the two colors with the total pulse energy conserved. Energy transfer from the laser pulse to the electronic system in silicon is dramatically enhanced by simultaneous dual-color irradiation and maximized at $\eta\sim 0.5$. Increased is the number of generated carriers, not the absorbed energy per carrier. The effect is more efficient for lower IR photon energy, or equivalently, larger vector-potential amplitude. As the underlying mechanism is identified the interplay between intraband electron motion in the {\it valence} band (before excitation) driven by the IR component and resonant valence-to-conduction interband excitation (carrier injection) induced by the UV component. The former increases excitable electrons which pass through the $k$ points of resonant transitions. The effect of different multiphoton absorption paths or intraband motion of carriers generated in the conduction band play a minor role.

Manifestation of hydration of Na+ and Cl− ions in the IR spectra of NaCl aqueous solutions in the range of 2750–4000 cm−1

This work is aimed at the study at studying the influence of the interaction of solvate shells on the profiles of the IR spectra of sodium chloride solutions in the 2750–4000 cm−1 range. The IR spectra of distilled water and sodium chloride solutions were obtained with the limit (0.356 g per 100 g of water) and 50 % of the limit (0.178 g per 100 g of water) concentrations at a temperature of 21˚. Theoretical methods based on the use of the DFT approach with the XLYP exchange–correlation potential are used to calculate the profiles of the IR spectra of clusters containing 9 water molecules per one NaCl molecule at the limit concentrations of the solution. In the case when the cluster contained a NaCl molecule, the spectra were calculated for interacting and non-interacting solvate shells in which the number of H2O molecules varied from 3 to 6. The expansion of the experimental band profile on a basis containing the profiles of the theoretical bands made it possible to study the features of NaCl hydration with a change in the concentration of solutions. It was found that the IR spectrum band is formed mainly by interacting Na+ and Cl- solvation shells, each containing 4 H2O molecules, while the ninth H2O molecule provides the bond between the solvated ions. As the salt concentration increases, the contribution of the solvation shells to the band profile increases too. The agreement reached in the positions and profiles of experimental and theoretical water bands at different solution concentrations substantiates the adequacy of the theoretical description of NaCl hydration. Theoretical studies explained the effect of a decrease in the band width, an increase in the peak intensity, and a shift of its maximum toward higher wavenumbers with increasing solution concentration.

Elucidating elusive quaternary selenide EuCeCuSe3: Synthesis, crystal structure, properties and theoretical studies

We report on the novel heterometallic quaternary selenide EuCeCuSe3, the fabrication of which has been a challenge until this work. The structure of the reported selenide was elucidated from the powder X-ray diffraction data, which revealed the formation of EuCeCuSe3 with excellent yield (96.7%) accompanied with a minor fraction of CeSe2 (3.3%), and was best solved in orthorhombic space group Pnma with the BaLaCuS3 structural type. Thus, the crystal structure of the title compound completes the row of the heterometallic quaternary selenides EuRECuSe3 (RE = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y), of which the cerium-based derivative exclusively belongs to the BaLaCuS3 structural type. The distortion of the CuSe4 polyhedron was compared for the whole series of EuRECuSe3 compounds using the τ4-descriptor for four coordinated ions, which revealed the highest degree of distortion for the Ce3+-containing selenide, followed by the La3+-based derivative. Furthermore, the crystallographic and geometrical parameters of the reported selenide were discussed in comparison to the Ce3+-based sulfides SrCeCuS3 and EuCeCuS3. Ab initio calculations of the crystal structure, a phonon spectrum and elastic constants for the crystal of EuСeCuSe3 were also performed. The types and wavenumbers of fundamental modes were determined and the involvement of ions participating in the phonon modes was assessed. The experimental IR spectrum of the reported selenide was interpreted and found to be in agreement with the calculated spectrum. The experimental direct band gap of EuCeCuSe3 was measured to be 1.36 eV that is consistent with the concept of its origin due to interband transitions between orbitals emerging mainly from 4f (valence band) and 5d (conduction band) levels of the Eu2+ cation. The dependence of the Young's modulus on the direction demonstrates the anisotropy of the elastic properties, while the Vickers hardness for EuCeCuSe3 was calculated to be 5.2 GPa. Finally, the title compound is paramagnetic above 4 K.