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First principle calculations of electronic, band structural, and optical properties of BixSr1-xTiO3 perovskite
摘要： Based on the first-principles plane-wave ultrasoft pseudopotential method, we set up models of perovskite-type oxides BixSr1-xTiO3 (x=0, 0.25, 0.5, 0.625, 1), and the geomertry optimization, the electronic and band structure were studied. The calculation results show that the binding energy decreases in BixSr1-xTiO3 after Sr2+ replaced by Bi3+. The calculations of the band structure show that BixBa1-xTiO3 are direct band gap semiconductors. The partial substitution of Bi3+ ions can increase the band gap and the absorption spectra ranges shift blue, and the values of band gaps are in the order of Bi0.625Sr0.375TiO3>Bi0.5Sr0.5TiO3>Bi0.25Sr0.75TiO3>SrTiO3>BiTiO3, and the absorption spectrum becomes wider in the order of Bi0.625Sr0.375TiO3>BiTiO3>Bi0.5Sr0.5TiO3>Bi0.25Sr0.75TiO3>SrTiO3. Based on the density of states, the top of the valence band is hybridized by O-2p and Sr-5s and the bottom of the conduction band state is mainly constituted by the Ti-3d state and Bi-6p. The regulation of photo-catalytic activity of the perovskite SrTiO3 can be realized by Bi ions substituting for Sr ions, and Bi-based perovskite BiTiO3 will be a potential photocatalytic material.
关键词： band gap,electronic structure,density of states,absorption spectra,BixSr1-xTiO3
更新于2025-09-10 09:29:36
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Molecular Mechanics Simulations and Improved Tight-Binding Hamiltonians for Artificial Light Harvesting Systems: Predicting Geometric Distributions, Disorder, and Spectroscopy of Chromophores in a Protein Environment
摘要： We present molecular mechanics and spectroscopic calculations on prototype artificial light harvesting systems consisting of chromophores attached to a tobacco mosaic virus (TMV) protein scaffold. These systems have been synthesized and characterized spectroscopically, but information about the microscopic configurations and geometry of these TMV-templated chromophore assemblies is largely unknown. We use a Monte Carlo conformational search algorithm to determine the preferred positions and orientations of two chromophores, Coumarin 343 together with its linker, and Oregon Green 488, when these are attached at two different sites (104 and 123) on the TMV protein. The resulting geometric information shows that the extent of disorder and aggregation properties, and therefore the optical properties of the TMV-templated chromophore assembly, are highly dependent on the choice of chromophores and protein site to which they are bound. We used the results of the conformational search as geometric parameters together with an improved tight-binding Hamiltonian to simulate the linear absorption spectra and compare with experimental spectral measurements. The ideal dipole approximation to the Hamiltonian is not valid since the distance between chromophores can be very small. We found that using the geometries from the conformational search is necessary to reproduce the features of the experimental spectral peaks.
关键词： tobacco mosaic virus (TMV),linear absorption spectra,spectroscopic calculations,artificial light harvesting systems,Monte Carlo conformational search,tight-binding Hamiltonian,molecular mechanics,chromophores
更新于2025-09-10 09:29:36
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A Frequency Range Selection Method for Vibrational Spectra
摘要： Theoretical calculations of vibrational properties are widely used to explain and predict experimental spectra. However, with standard quantum chemical methods all molecular motions are considered, which is rather time-consuming for large molecules. As typically only a specific spectral region is of experimental interest, we propose here an efficient method that allows calculation of only a selected frequency interval. After a computationally cheap low-level estimate of the molecular motions, the computational time is proportional to the number of normal modes needed to describe this frequency range. Results for a medium-sized molecule show a reduction in computational time of up to one order of magnitude with negligible loss in accuracy. We also show that still larger computational savings are possible by using an additional intensity-selection procedure.
关键词： frequency range selection,IR absorption spectra,quantum chemical methods,vibrational spectra,computational efficiency
更新于2025-09-09 09:28:46
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Spectral signatures of fluorescence and light absorption to identify crude oils found in the marine environment
摘要： To protect the natural marine ecosystem, it is necessary to continuously enhance knowledge of environmental contamination, including oil pollution. Therefore, to properly track the qualitative and quantitative changes in the natural components of seawater, a description of the essential spectral features describing petroleum products is necessary. This study characterises two optically-different types of crude oils (Petrobaltic and Romashkino) – substances belonging to multi-fluorophoric systems. To obtain the spectral features of crude oils, the excitation-emission spectroscopy technique was applied. The fluorescence and light absorption properties for various concentrations of oils at a stabilised temperature are described. Both excitation-emission spectra (EEMs) and absorption spectra of crude oils are discussed. Based on the EEM spectra, both excitation end emission peaks for the wavelength-independent fluorescence maximum (Exmax/Emmax) – characteristic points for each type of oil – were identified and compared with the literature data concerning typical marine chemical structures.
关键词： seawater,Excitation-emission spectra,fluorescence spectroscopy,oil pollution,absorption spectra
更新于2025-09-09 09:28:46
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White light-emitting Dy <sup>3+</sup> -doped transparent chloroborosilicate glass: synthesis and optical properties
摘要： Dy3+-doped chloroborosilicate glasses with the composition 35.7SiO2-25.5B2O3-17BaO-3.4K2O-3.4Al2O3-15BaCl2 (mol%) were prepared using melt quenching technique. The glass transition temperature (Tg) was ~610°C. In UV-Vis-NIR absorption spectra characteristic absorption bands of Dy3+ appeared at 322, 347, 364, 388, 795 and 880 nm due to spectral transitions from the 6H15/2 level to various higher levels of Dy3+ ion. The excitation spectrum was recorded at within 200–550 nm by monitoring emissions at 576 nm. The excitation bands at 392, 428, 453 and 472 nm were attributed to the 6H15/2 → 4I13/2, 4G11/2, 4I15/2 and 4F9/2 transitions, respectively. Prominent emission bands were observed at wavelengths of 484, 576, 664 and 754 nm when excited at 447 nm. The bands correspond to the transitions 4F9/2→6H15/2, 4F9/2 → 6H13/2, 4F9/2 → 6H11/2, and 4F9/2 → 6H9/2 6F11/2 respectively. The emitted light from all the samples were found to be white. Their colour coordinates lie within the white range. The sample containing 0.5 wt% Dy2O3 emitted white light with the colour coordinates x=0.351, y=0.335, which are the very closest to pure white light and whose colour temperature of 4716 K is similar to daylight. Such white light-emitting transparent glasses promise to be enormously useful for various photonic applications.
关键词： white light generation,chloroborosilicate glass,Dy3+-doped glass,photoluminescence,absorption spectra
更新于2025-09-09 09:28:46
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Analytical fitting of temperature-dependent spin-flip transitions in absorption spectra of Cr3+-doped silicate glasses
摘要： Temperature-dependent optical absorption spectra have been recorded for Cr3+ doped silicate glasses between 10 K and 773 K. Due to the intermediate ligand field strength of the Cr3+ coordination environment, overlap of the lowest-energy spin-allowed 4A2 → 4T2 band and the two spin-forbidden transitions to the 2E and 2T1 states at approximately 650 nm results in interference dips. An analytical model equation is fitted to the spectra and electronic structure parameters extracted. This represents the first time that variations of these parameters with temperature are obtained over a large temperature range, revealing characteristics of all three overlapping d-d transitions.
关键词： Chromium(III) doped glasses,absorption spectra,spectra calculations,interference dips,temperature
更新于2025-09-04 15:30:14
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Bismuth doped lead-free two-dimensional tin based halide perovskite single crystals
摘要： Heterovalent-metal doping is an efficient tool to tune the optoelectronic properties of the famous halide perovskites. Previous studies have focused on the heterovalent-doping in three-dimensional (3D) halide perovskites. However, there is a lack of such doping in two-dimensional perovskites which possess unique optoelectronic properties and improved chemical stability as compared to 3D analogues. Here, we present successful doping of Bismuth into the lattice of lead-free, two-dimensional perovskite PEA2SnBr4 single crystals. Structural characterizations demonstrate that the doped crystals possess identical crystal structure and layered morphology with the pristine one. Intriguingly, we find the PL peak and spectral shape can be tailored by tuning the concentration of Bi dopants. Femtosecond transient absorption spectroscopy is performed to understand the underlying mechanism related to tunable PL behaviors, and a clear picture of the Bismuth-doping impact is provided.
关键词： Global analysis fit,Femtosecond transient absorption spectra,Self-trapped excitons,Photoluminescence,Heterovalent-metal doping
更新于2025-09-04 15:30:14