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- 2019
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Enhancing light absorption by colloidal metal chalcogenide quantum dots <i>via</i> chalcogenol(ate) surface ligands
摘要： Chemical species at the surface (ligands) of colloidal inorganic semiconductor nanocrystals (QDs) markedly impact the optoelectronic properties of the resulting systems. Here, post-synthesis surface chemistry modification of colloidal metal chalcogenide QDs is demonstrated to induce both broadband absorption enhancement and band gap reduction. A comprehensive library of chalcogenol(ate) ligands is exploited to infer the role of surface chemistry on the QD optical absorption: the ligand chalcogenol(ate) binding group mainly determines the narrowing of the optical band gap, which is attributed to the np occupied orbital contribution to the valence band edge, and mediates the absorption enhancement, which is related to the π-conjugation of the ligand pendant moiety, with further contribution from electron donor substituents. These findings point to a description of colloidal QDs that may conceive ligands as part of the overall QD electronic structure, beyond models derived from analogies with core/shell heterostructures, which consider ligands as mere perturbation to the core properties. The enhanced light absorption achieved via surface chemistry modification may be exploited for QD-based applications in which an efficient light-harvesting initiates charge carrier separation or redox processes.
关键词： colloidal metal chalcogenide quantum dots,light absorption,optoelectronic properties,surface ligands,band gap reduction
更新于2025-10-22 19:40:53
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Tin( <scp>ii</scp> ) thiocyanate Sn(NCS) <sub/>2</sub> – a wide band gap coordination polymer semiconductor with a 2D structure
摘要： Semiconductors based on tin(II) show promising hole-transport characteristics due to the 5s electrons that form the valence band. In this paper, we report the synthesis and comprehensive characterization of tin(II) thiocyanate [Sn(NCS)2] and identify it as a novel transparent coordination polymer semiconductor. The single crystal X-ray analysis reveals covalently-bonded 1D polymeric chains that form a 2D structure through Sn–S tetrel bonds. Density functional theory calculations also confirm the importance of the van der Waals interactions between the 2D sheets. Furthermore, we show that the s character of Sn(II) is maintained at the top of the valence band, resulting in dispersed states with a small hole effective mass. The coordination with NCS ligands also leads to a conduction band which is high in energy, giving rise to a wide band gap and excellent transparency in the visible spectrum. This is the first report on the electronic properties of Sn(NCS)2 which highlights the potential of developing new transparent semiconductors based on thiocyanate coordination polymers.
关键词： hole transport,band gap,tin(II) thiocyanate,transparent,semiconductor,coordination polymer
更新于2025-10-22 19:40:53
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An experimental and theoretical study of the structural ordering of the PTB7 polymer at a mesoscopic scale
摘要： Our extensive study based on optoelectronic and electric measurements (which consisted of: UV-Vis absorption, photoluminescence, surface photovoltage measurement, charge extraction by linearly increasing voltage, and energy-resolved electrochemical impedance spectroscopy) revealed the fundamental role of the thickness of the formation of intra- and interchain interaction in poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) films. We have shown that the final optoelectronic and electronic properties of PTB7 films are governed by the structural ordering development of the transition from nano- to submicroscale. The ordering of polymer chains and competition between the formation of J- and H-aggregates results in a non-trivial dependence of luminescence, exciton diffusion length, transport band gap, and defect concentration. According to a theoretical analysis, the driving forces responsible for the observed phenomena are associated with the thickness threshold dependence of the thin film drying mode which can proceed with or without the polymer skin formation on the surface of forming film.
关键词： low band-gap,thickness dependences,Conjugated polymers
更新于2025-10-22 19:40:53
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The bright side of PV production in snow-covered mountains
摘要： Our work explores the prospect of bringing the temporal production profile of solar photovoltaics (PV) into better correlation with typical electricity consumption patterns in the midlatitudes. To do so, we quantify the potential of three choices for PV installations that increase production during the winter months when electricity is most needed. These are placements that favor (i) high winter irradiance, (ii) high ground-reflected radiation, and (iii) steeper-than-usual panel tilt angles. In addition to spatial estimates of the production potential, we compare the performance of different PV placement scenarios in urban and mountain environments for the country of Switzerland. The results show that the energy deficit in a future fully renewable production from wind power, hydropower, and geothermal power could be significantly reduced when solar PV is installed at high elevations. Because the temporal production patterns match the typical demand more closely than the production in urban environments, electricity production could be shifted from summer to winter without reducing the annual total production. Such mountain installations require significantly less surface area and, combined with steeper panel tilt angles, up to 50% of the winter deficit in electricity production can be mediated.
关键词： panel tilt,seasonal energy gap,renewable energy,photovoltaic,surface reflectance
更新于2025-09-23 15:23:52
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Novel solid polymer electrolyte based on PMMA:CH3COOLi effect of salt concentration on optical and conductivity studies
摘要： Novel solid polymer electrolyte (SPE) films based on poly(methyl methacrylate) (PMMA) and lithium acetate (CH3COOLi) with different weight ratios of PMMA:CH3COOLi wt% (60:40, 70:30, 80:20 wt%) were prepared by solution casting technique. XRD analysis confirmed the amorphous nature of Li–PMMA SPE films. FTIR analysis revealed the structural changes in polymer by complexation with Li salt. From the optical absorbance studies, the value of lowest energy band gap was found to be 3.06 eV for the composition, PMMA:CH3COOLi (60:40 wt%). From AC impedance studies, the highest value of ionic conductivity 8.21 × 10?5 S/cm at 303 K for the SPE film PMMA:CH3COOLi (60:40 wt%) is observed compared to the reported literature. From the results of Li–PMMA SPE film with high ionic conductivity, it is a promising material for the application of solid-state battery.
关键词： Band gap,Ionic conductivity,Dielectric measurements,Li–PMMA SPE
更新于2025-09-23 15:23:52
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Band gap analysis of periodic structures based on cell experimental frequency response functions (FRFs)
摘要： An approach is proposed to estimate the transfer function of the periodic structure, which is known as an absorber due to its repetitive cells leading to the band gap phenomenon. The band gap is a frequency range in which vibration will be inhibited. A transfer function is usually performed to gain band gap. Previous scholars regard estimation of the transfer function as a forward problem assuming known cell mass and stiffness matrices. However, the estimation of band gap for irregular or complicated cells is hardly accurate because it is difficult to model the cell exactly. Therefore, we treat the estimation as an inverse problem by employing modal identification and curve fitting. A transfer matrix is then established by parameters identified through modal analysis. Both simulations and experiments have been performed. Some interesting conclusions about the relationship between modal parameters and band gap have been achieved.
关键词： Band gap,Periodic structure,Transfer matrix,Parameter identification,Modal analysis
更新于2025-09-23 15:23:52
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Photostable coumarin containing azo dyes with multifunctional property
摘要： A series five coumarin azo disperse dyes with thiophene bridge are synthesized using diazotized aniline derivatives which are confirmed by FT-IR, 1H NMR, 13C NMR, and CHN analysis. The dyes are applied on polyester and nylon material. The multifunctional properties (lightfastness, washing fastness, sublimation fastness, K/S, UPF, and antimicrobial activity) of the dyed fabric are determined. The dye 3a (-NO2) show red shifted absorption (649 nm) and blocking 95.5-97.4% of UV radiations with 96% antimicrobial property. The geometries of all the azo dyes are optimized using Density Functional Theory (DFT). The Global Reactivity Descriptors (GRD) are evaluated at the same method of theory. The GRD obtained shows a linear relation with lightfastness and UPF ratings. The antimicrobial activity of all synthesized dyes are determined by AATCC 100 test method and it is correlated with the HOMO-LUMO energy band gap.
关键词： UPF,fastness property,Coumarin-azo dyes,global reactivity descriptors,HOMO-LUMO gap,antimicrobial activity
更新于2025-09-23 15:23:52
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Composition Dependence of the Band Gap Energy of the Sb-Rich GaBixSb1?x Alloy (0?≤?x?≤?0.26) Described by the Modified Band Anticrossing Model
摘要： The impurity–host interaction and the impurity–impurity interaction exist in the Sb-rich GaBixSb1?x alloy. It is found that the effect of impurity–impurity on the band gap energy can be neglected. The impurity–host interaction not only depends on the Bi content, but also on the content of the host material. In order to describe the band gap energy of the Sb-rich GaBixSb1?x, the virtual crystal approximation for conduction band minimum (CBM) and the modified valence band anticrossing model for valence band maximum (VBM) are applied. It is also found that when the Bi content is about 0.259, the band gap energy of GaBixSb1?x becomes 0 eV. In addition, it is found that the U CBM depending on Bi content is much stronger than that of the U VBM. It is relative to two factors. One is that the conduction band offset between GaSb and GaBi is much larger than the valence band offset. The other is that the energy difference between the Bi level and the U VBM of GaSb is very large. The large energy difference usually leads to a weak coupling interaction between the Bi level and the U VBM of GaSb, thus resulting in weak composition dependence of the U VBM in the Sb-rich range.
关键词： Bi level,band gap energy,Sb-rich,GaBixSb1?x
更新于2025-09-23 15:23:52
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Progress in development of a new luminescence setup at the FinEstBeAMS beamline of the MAX IV laboratory
摘要： FinEstBeAMS is a new materials science beamline at the 1.5 GeV storage ring of the MAX IV Laboratory in Lund, Sweden. It has been built based on grazing incidence monochromatization of synchrotron light, which allows to cover a remarkably wide excitation energy range from ultraviolet to soft x-rays (4.5-1450 eV). A new mobile luminescence spectroscopy end station has been commissioned with design benefitting from the advantages of a high flux elliptically polarizing undulator light source. We report on the design of the luminescence end station, its technical realization and performance achieved so far. Special attention is paid to the experimental challenges for luminescence spectroscopy under grazing incidence excitation conditions. The first luminescence results obtained demonstrate a reliable performance of the advanced setup at FinEstBeAMS.
关键词： Luminescence spectroscopy,synchrotron radiation,wide gap compounds,VUV – XUV photoexcitation
更新于2025-09-23 15:23:52
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Study on Band-Gap Behaviors of 2D Hierarchical Re-Entrant Lattice Structures
摘要： An investigation of Poisson’s ratios and band gap behaviors of 2D hierarchical re-entrant lattice structures is conducted using finite element method (FEM). The structure with a hierarchy order n (n≥1) is constructed by replacing each outmost vertex of the re-entrant octagons of a hierarchical structure of hierarchy order n?1 with a smaller self-similar re-entrant octagon. The dispersion relation and transmission spectrum of the proposed hierarchical structures are analyzed based on the Bloch’s theorem. The effects of geometrical parameters, order of rotational symmetry and orientation angle of some types of re-entrant polygon cores on the lattice Poisson’s ratio and band gap structures are also investigated. Results show that the re-entrant structures with first order hierarchy exhibit a wider band gap and a stronger attenuation effect compared with structures without structural hierarchy. The first order 2D hierarchical re-entrant structure with a negative Poisson’s ratio of ?0.032 exhibits the widest band gap, 17.8% wider than that of the zeroth order 2D re-entrant structure. The order of rotational symmetry and the orientation angle of the re-entrant polygon cores of the lattice have a strong impact on the lattice Poisson’s ratio and band structures.
关键词： re-entrant,negative Poisson’s ratio,band gap,hierarchical structure,transmission spectrum
更新于2025-09-23 15:23:52