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Rational design of visible light panchromatic absorption laser dye molecules: The first principle study
摘要： Laser dye molecules play an important role in tunable lasers due to enhancing the laser radiation intensity and increasing the laser adjustable range. The broad spectral bandwidth and visible light absorption allows for the evaluation of multiple fluorescence quenching mechanisms such as excition formation, photoinduced electron transfer, and excited-state proton transfer. A series of organic dye molecules (LD1-4、LA2-5、LU1-5、LV1-4、LI1-4) consisting of simple electron donor (D), conjugated bridge (π) and electron acceptor (A) units were designed using first-principles calculations in order to evaluate their potential for applications in tunable lasers. Furthermore, the optical and electronic properties of the dye molecules are analyzed in detail using density functional theory (DFT) and time-dependent density functional theory (TDDFT), including spectral parameters, energy levels and orbital contributions of organic dye molecules. The results indicate that LI1-3 show high molar extinction coefficient, visible light full color absorption and obvious red-shifted compared to the experimentally synthesized dye LA3. In particular, the newly designed LI3 exhibits not only a 190 nm red-shifted and a higher molar extinction coefficient with an increment of 19%, but also has an extremely broad absorption spectrum covering entire visible absorption spectrum from 380 to 750 nm compared to LD1. We also find that the dyes with dithiophene groups and naphthalene group as the electron donors are better absorption spectrum than dyes with double bond group and benzene group. These calculated results will hopefully contribute to the further development of novel laser dye molecules and further provide scientific support and theoretical guidance for subsequent related research.
关键词： Absorption spectra,Laser dye,DFT/TDDFT,Panchromatic absorption
更新于2025-09-11 14:15:04
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Optical Properties of Buckled Bismuthene
摘要： In this paper, the optical properties of buckled bismuthene (a new 2D material) are studied in different strains. Different transitions in bismuthene’s band structure are mentioned and the optical advantages of buckled bismuthene are discussed. It is found that buckled bismuthene is strain independent infrared (IR) reducer and could be used in bio photonics.
关键词： 2D material,optical properties,reflection,group V monolayers,honeycomb lattice,absorption spectra,density functional theory,dielectric function,buckled bismuthene
更新于2025-09-11 14:15:04
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The Radioprotective Effects of Low-Intensity Laser Radiation on Rat Peripheral Blood Cells
摘要： The radioprotective effect of low-intensity laser radiation on blood cells was studied on Wistar rats. The following procedures was carried out: single total body γ-radiation (dose of 3 Gy) of rats; over-vein irradiation with continuous laser radiation (λ = 670 nm); and combined γ- and laser irradiation, which varied among different series of experiments according to the number of procedures and the energy density of the laser radiation (2.5 J/cm2, 1.25 J/cm2). The influence of γ- and laser radiation on the number of peripheral blood cells in rats, the activity of antioxidant defense enzymes (superoxide dismutase and catalase), and on the blood absorption spectra in regions sensitive to its oxygenation were studied. On the 4th day after γ-irradiation, the radioprotective effect of low-intensity laser radiation was manifested as an increase in the average number of leukocytes (up to 1.4 times) and lymphocytes (up to 1.8 times) in comparison with reduced γ-irradiation, in an increase in the relative lymphocyte proportion in the leukocyte population (up to 1.5 times), and in an increase in the activities of catalase and superoxide dismutase, which were decreased by the γ-irradiation. It was found that the changes in the number of erythrocytes, leukocytes, lymphocytes, and superoxide dismutase activity initiated by γ-radiation alone and by combined laser and γ-radiation differed in individual rats and depended on individual initial values. The molecular mechanisms of the observed photo-radiobiological effects are discussed.
关键词： low-intensity laser radiation,blood absorption spectra,γ-radiation,blood cells,antioxidant defense enzymes
更新于2025-09-11 14:15:04
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Dot size variability induced changes in the optical absorption spectra of interdiffused quantum dot systems
摘要： In this work, we have quantified the effects of dot size variability on the interband optical absorption spectra of interdiffused III–V quantum dot (QD) systems through analytical models which agree well with experimental data. The variability function induced due to inhomogeneous nature of dot size distribution has been considered to be Gaussian in nature, where individual dots have been assumed to be lens-shaped having inhomogeneous material composition inside the dot. This is necessary to consider any realistic interdiffused system. Such an assumption is not in line-up with the conventional methodologies reported earlier on the subject, where the QD composition was considered to be homogeneous, presenting an ideal or quasi-ideal situation which may be applicable only for dot structures in absence of interdiffusion. Moreover, for the first time, the effects of dot size variability and interdiffusion on the optical spectra of QD systems have been analysed in the same platform. The effects of dot size deviation, QD aspect ratio, core group III content inside the dot, standard deviation, and so on, on the optical absorption spectra have been demonstrated.
关键词： Dot size variability,III–V semiconductors,Optical absorption spectra,Interdiffusion,Quantum dots
更新于2025-09-11 14:15:04
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Effect of Annealing on Optical Properties of Zinc Oxide Thin Films Prepared by Homemade Spin Coater
摘要： Zinc oxide (ZnO) thin films were deposited on the ordinary glass substrates by spin coating method. The precursor solution was prepared by mixing zinc acetate dihydrate in appropriate proportions with ethanol and diethanolamine (DEA). The obtained thin films were dried at 200oC for 15 minutes in hot air oven. Crystalline ZnO thin films were achieved following annealing process at temperatures 300o, 400o and 500oC for 2 hours. Thin films as- prepared were studied by X-ray diffraction and UV-visible spectroscopy. The films were transparent from near ultraviolet to infrared region. Optical band gap energy of ZnO was obtained 3.22 eV at 300oC. On annealing at 400o and 500oC, band gap energy was shifted at 3.14 eV and 3.05 eV respectively.
关键词： annealing,absorption spectra,sol-gel method,zinc oxide,band gap energy
更新于2025-09-11 14:15:04
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Electronic structures and spectroscopic signatures of silicon-vacancy containing nanodiamonds
摘要： The presence of midgap states introduced by localized defects in wide-band-gap-doped semiconductors can strongly affect the electronic structure and optical properties of materials, generating a wide range of applications. Silicon-divacancy defects in diamond have been recently proposed for probing high-resolution pressure changes and performing quantum cryptography, making them good candidates to substitute for the more common nitrogen-vacancy centers. Using group-theory and ab initio electronic structure methods, the molecular origin of midgap states, zero-phonon line splitting, and size dependence of the electronic transitions involving the silicon-vacancy center is investigated in this paper. The effects of localized defects on the Raman vibrational and carbon K-edge x-ray absorption spectra are also explored for nanodiamonds. This paper presents an important analysis of the electronic and vibrational structures of nanosized semiconductors in the presence of midgap states due to localized defects, providing insight into possible mechanisms for modulating their optical properties.
关键词： midgap states,electronic structure,optical properties,nanodiamonds,Raman vibrational spectra,quantum cryptography,x-ray absorption spectra,silicon-vacancy defects
更新于2025-09-10 09:29:36
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AgI-BiOI-graphene composite photocatalysts with enhanced interfacial charge transfer and photocatalytic H2 production activity
摘要： BiOI-based photocatalysts were proved to exhibit photocatalytic H2 production activity. AgI-BiOI-graphene showed better H2 production activity than BiOI and BiOI-graphene. The surface chemistry, electronic property, phase structure, morphology, optical property and photocatalytic performance of these photocatalysts were studied. The interfacial electronic states of the photocatalysts were investigated through their C K-edge near-edge X-ray-absorption fine-structure (NEXAFS) spectra. Based on the in situ NEXAFS spectra measured with and without illumination, a mechanism about the transport of photoelectron from AgI to graphene through BiOI is proposed for the photocatalytic H2 production process. The incorporation of graphene restricted the three-dimensional self-assembly of BiOI nanocrystals and led to the formation of less extensively crystallized BiOI domains through a confined-space effect. Addition of AgNO3 precursor altered the crystal structure of BiOI from flower-like to horizontally stacked flat plates. The results of NEXAFS spectra, photoluminescence spectra and photocurrent tests reveal that the improved photocatalytic activity of the AgI-BiOI-graphene photocatalyst is attributable to the interfacial interaction among AgI, BiOI and graphene, which enhanced the separation of photogenerated electrons to generate H2. AgI-BiOI-graphene photocatalyst was a stable photocatalyst for the production of H2. After three cycles, 86 % activity of recycled photocatalysts was retained.
关键词： X-ray absorption spectra,Near edge X-ray absorption fine structure,Interfacial electronic states,Photocatalytic H2 production,BiOI
更新于2025-09-10 09:29:36
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Comparison and convergence of optical absorption spectra of noble metal nanoparticles computed using linear-response and real-time time-dependent density functional theories
摘要： The real-time time-dependent density functional theory (RT-TDDFT) is rapidly gaining prominence as an alternative approach to capture optical properties of molecular systems, which warrants the necessity to benchmark the traditional linear response (LR) method and the RT approach. We calculate the absorption spectra of noble metal nanoparticles with a variety of sizes and shapes to demonstrate the consistency of the two methods over a broad range of energy. The RT spectrum obtained using a grid-based basis set with pseudopotentials achieves results in good agreement with the LR spectrum obtained with large QZ4P atom-centered basis sets. Factors that lead to convergence of the spectra are considered. In addition, the real-time variation of the electron density is visualized to show the collective oscillation of electron density for the plasmon modes of noble metal nanoparticles. The RT approach is most useful when calculating wide absorption spectra of larger gold or silver nanoparticles.
关键词： optical absorption spectra,noble metal nanoparticles,RT-TDDFT,LR-TDDFT,plasmon modes
更新于2025-09-10 09:29:36
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On the Fractal Absorption Spectra of Polymers in the Low-Frequency Part of the Terahertz Range
摘要： The power dependence α(ν) ∝ νμ, where μ > 0 is the power exponent which is noninteger in the general case, is observed for amorphous polymers with a small absorption coe?cient α in the low-frequency part of the terahertz range, which approximately corresponds to the frequencies ν from 0.1 to 2–3 THz. This dependence is fractal, which is due to the fractal structure of the polymer macromolecules. In this work, we ?nd the power-law index at room temperature for the absorption coe?cient of some amorphous polymers. This index is determined on the basis of the dynamics of transmission of a broadband picosecond terahertz pulse through the polymer sample, i.e., using the method of the pulse terahertz spectroscopy in the time-domain representation.
关键词： terahertz range,fractal absorption spectra,polymers,fractal structure,power-law index
更新于2025-09-10 09:29:36
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Tailoring the Structural and Optical Parameters of Eu3+:CeO2-SiO2 Nanopowder Via Thermal Treatment
摘要： Nanocrystalline Eu3+:CeO2-SiO2 powder samples were prepared by sol-gel technique. This technique is suitable for large-scale production and it is also a cost effective process. The prepared samples were annealed at different temperatures which were characterized by many complementary techniques. The formation of cubic fluorite structure of CeO2 nanocrystal with a uniform distribution was confirmed by x-ray diffraction (XRD) and transmission electron microscopy (TEM). The average nanocrystalline size has been calculated as 3, 7 and 15 nm using Debye-Scherrer formula for different annealed samples. The calculated nanocrystalline sizes were compared with W-H plot and TEM histograms. It was investigated that FWHM of diffraction peaks decreases with increase in temperature results in increase nanocrystalline size. The FTIR spectroscopy provides the valuable information and identification of different chemical group/bonds present in the prepared samples. It is found that if we fixed the dopant concentration, then particle size, morphology and band gap energy of prepared nanopowder can be tailored by applying the annealing conditions. Comparative studies of absorption spectra and corresponding band gap energies have been done and a red shift has been observed in absorption spectra with thermal treatment. The shift of the optical absorption edge of prepared nanopowder towards lower energies increases its utilization in the visible region specially photocatalytic activity.
关键词： Thermal annealing,Absorption spectra,Structural properties,Nanopowder,Band gap energy
更新于2025-09-10 09:29:36