Optical Band Shape Research Articles

Bamboo-mediated silver nanoparticles functionalized with activated carbon and their application for non-enzymatic glucose sensing

A precise sensor to quickly identify glucose concentration is important for diabetic patients. In this study, the silver nanoparticles (Ag NPs) were synthesized by a green method using bamboo leaves extract solution. These Ag NPs were used for the functionalization of bamboo activated carbon (BAC) through chemical route with various weight percentages AgNPs/BAC 1 wt%, AgNPs/BAC 2 wt%, AgNPs/BAC 3 wt%, and these are used as an active modified electrode to fabricate non-enzymatic electrochemical sensors for detection of glucose content (in blood samples of the patients). The optical band gap, morphology, shape, size, and functional compositions were studied using advanced analytical techniques such as X-ray diffraction, UV–visible, FESEM, TEM, and FTIR spectra analysis. Moreover, the screen-printed gold electrode (SPGE) was used as a bare electrode, and electrochemical performance was done with the help of cyclic voltammetry. The Ag NPs/BAC 2 wt% showed better catalytic activity towards the glucose detection with an excellent sensitivity of 1872.32 µA mM−1 cm−2 and a limit of detection (LOD) of 0.2 µM within the linear range of 1 mM-2 mM. Based on this study, the AgNPs/BAC 2 wt% sample can be assumed to be an eco-friendly, low-cost glucose biosensor.

Quantum-Classical Electron as an Organizing Principle in Nature

We are introducing briefly to the new theory of “quantum” transitions in molecular and chemical physics — quantum-classical mechanics, in which an electron behaves dynamically in two ways: both as a quantum and as a classical elementary particle. Namely, in the initial and final adiabatic states of molecular “quantum” transitions, the light electron exhibits its quantum properties. On the contrary, in the transient molecular state, the electron, provoking the so-called dozy chaos in the vibrational motion of very heavy nuclei “in order” to shift the equilibrium positions of their vibrations to new positions corresponding to the new distribution of the electron charge, because of the continuous energy spectrum in the transient state, manifests itself as a classical elementary particle. The article discusses mainly studied and some promising applications of the organizing role of an electron in nature. Among the well-studied applications, the quantum-classical organization of optical absorption band shapes in polymethine dyes and their J-aggregates is discussed. For example, the well-known narrow and intense J-band of J-aggregates is one of the striking examples of the implementation of the so-called Egorov resonance, in which the motion of the reorganization of the nuclei of the environmental medium significantly contributes to the electron transition in the optical pi-electron chromophore of J-aggregates. This effect can also be interpreted as the transfer of dozy chaos from the peak of the J-band into its wing by a chaotic motion of the quantum-classical pi-electron state of the J-chromophore. The dynamic role of the quantum-classical electron in the joint organization of the absorption and luminescence spectra, and an extension of quantum-classical mechanics to nonlinear optical processes are discussed. The probable leading role of quantum-classical electrons in the evolution of molecular matter and possibility of applications of quantum-classical mechanics to the study of cancer and viruses are discussed as a future research perspective.

Modal optimisation within the time-independent eigenstate-free Raman wavefunction formalism

The time-independent eigenstate-free Raman wavefunction approach, which is based on the vibrational inhomogeneous Schrödinger equation (ISE), is a promising alternative to the well-known sum-over-states and time-dependent methods for the calculation of optical bandshapes and resonance Raman intensities. The solution of the ISE, the Raman wavefunction (RWF), can be obtained within a vibrational configuration interaction (VCI) ansatz. In this method, the optimisation of vibrational modals can provide a better convergence of the calculated RWF towards the full VCI limit. For this purpose, the variational principle for the ISE problem is formulated. The variational condition for the modal functions leads to the complex inhomogeneous vibrational self-consistent field equations. The key aspects of the implementation of this approach are discussed. The performance of this method in comparison with the conventional scheme involving VCI bases of different quality is illustrated for the X ~ 2 A 2 ⟵ X ~ 1 A 1 transition in furan. The quantitative effects due to the modal optimisation are found to be relatively small, as compared to the impact of moderate extension of the configuration basis.

Quantum-classical mechanics: Luminescence spectra in polymethine dyes and J-aggregates. Nature of the small Stokes shift

Abstract It can be shown that the joint and full-fledged (beyond the adiabatic approximation) motion of light electrons and very heavy nuclei in molecular and chemical physics in the framework of quantum mechanics can be only singular. This singularity is damped in a new theoretical approach called dozy-chaos mechanics or quantum-classical mechanics. Earlier, the effectiveness of the damping procedure for the above singularity was demonstrated in the simplest case of quantum-classical mechanics (of quantum-classical transitions), namely, by quantum-classical mechanics of elementary electron-charge transfers in condensed media and its applications to the shape of optical absorption bands in polymethine dyes and their aggregates and to other problems. In this article, on the basis of the quantum-classical mechanics of elementary electron-charge transfers, we find out the nature of the luminescence band shape and the small Stokes shift in polymethine dyes and J-aggregates. The very small experimental value of the Stokes shift (1 nm in the J-band) is explained by two factors, both of which are associated with a high degree of self-organization of molecular quantum transitions in J-aggregates. The first of these is related to the stimulation of the electronic transition in the J-chromophore by the chaotic dynamics (weak dozy chaos) of the reorganization of the nuclear environment, which leads to the well-known narrow and red-shifted absorption J-band. The second factor is associated with the spontaneous loosening of the excited electronic state immediately before the act of the photon’s creation by the electron in spontaneous emission. For polymethine dyes and J-aggregates, the universal effect of spontaneous dynamic loosening turns out to be abnormally strong, it must be supposed, due to the very extended π -electron systems undergoing the quantum-classical transitions there. A quantitative explanation is also given for the position and shape of the optical bands in J-aggregates for luminescence and optical absorption in the case of an admixture of monomers of a polymethine dye in an aqueous solution. The experimental fact of the absence of the optical band of the monomers on the shortwave wing of the J-band of luminescence with its apparent presence on the shortwave wing of the J-band of optical absorption is explained by a significant increase in the dynamic self-organization of quantum-classical transitions in J-aggregates as compared to just a small increase in the dynamic self-organization of these transitions in monomers upon the change from optical absorption to luminescence.

Tuning the electronic properties and interfacial interactions of WS2/ZrO2(001) heterostructures by an external electric field, interlayer coupling and monolayer to few–layer of WS2 sheets

Abstract Understanding the connection between interfacial interactions and electronic properties are vital for the fabrication of ZrO2–based optoelectronic and nanoelectronics materials with desirable properties. In this study, the interfacial interactions, optical and electronic properties of WS2/ZrO2(001) heterostructures in the presence of an external electric field, interlayer coupling and monolayer to few–layer WS2 sheets is investigated for the first time using a first–principle calculation. The charge density distribution and Mulliken population charge analysis reveal that the charge carriers can effectively separate in the layered WS2/ZrO2 interface. The optical absorption spectra and band shape of these hybrid heterostructures are similar, with their bandgap decreases, as well as their charge transfer and redshift of the absorption edge increase upon increasing the number of WS2 sheets. Moreover, by varying the interlayer coupling or by applying a suitable external electric field with different strengths, the cohesion energy, work function and bandgap energy of WS2/ZrO2(001) heterostructure can be effectively tuned. These theoretical results are expected to offer useful insights into the design of future optoelectronic and nanoelectronic devices based on two–dimensional van der Waals heterostructures.

Nonempirical Simulations of Inhomogeneous Broadening of Electronic Transitions in Solution: Predicting Band Shapes in One- and Two-Photon Absorption Spectra of Chalcones.

We have examined several approaches relying on the Polarizable Embedding (PE) scheme to predict optical band shapes for two chalcone molecules in methanol solution. The PE-TDDFT and PERI-CC2 methods were combined with molecular dynamics simulations, where the solute geometry was kept either as rigid, flexible or partly-flexible (restrained) body. The first approach, termed RBMD-PE-TDDFT, was employed to estimate the inhomogeneous broadening for subsequent convolution with the vibrationally-resolved spectra of the molecule in solution determined quantum-mechanically (QM). As demonstrated, the RBMD-PE-TDDFT/QM-PCM approach delivers accurate band widths, also reproducing their correct asymmetric shapes. Further refinement can be obtained by the estimation of the inhomogeneous broadening using the RBMD-PERI-CC2 method. On the other hand, the remaining two approaches (FBMD-PE-TDDFT and ResBMD-PE-TDDFT), which lack quantum-mechanical treatment of molecular vibrations, lead to underestimated band widths. In this study, we also proposed a simple strategy regarding the rapid selection of the exchange-correlation functional for the simulations of vibrationally-resolved one- and two-photon absorption spectra based on two easy-to-compute metrics.

Nature of the optical band shapes in polymethine dyes and H-aggregates: dozy chaos and excitons. Comparison with dimers, H*- and J-aggregates.

Results on the theoretical explanation of the shape of optical bands in polymethine dyes, their dimers and aggregates are summarized. The theoretical dependence of the shape of optical bands for the dye monomers in the vinylogous series in line with a change in the solvent polarity is considered. A simple physical (analytical) model of the shape of optical absorption bands in H-aggregates of polymethine dyes is developed based on taking the dozy-chaos dynamics of the transient state and the Frenkel exciton effect in the theory of molecular quantum transitions into account. As an example, the details of the experimental shape of one of the known H-bands are well reproduced by this analytical model under the assumption that the main optical chromophore of H-aggregates is a tetramer resulting from the two most probable processes of inelastic binary collisions in sequence: first, monomers between themselves, and then, between the resulting dimers. The obtained results indicate that in contrast with the compact structure of J-aggregates (brickwork structure), the structure of H-aggregates is not the compact pack-of-cards structure, as stated in the literature, but a loose alternate structure. Based on this theoretical model, a simple general (analytical) method for treating the more complex shapes of optical bands in polymethine dyes in comparison with the H-band under consideration is proposed. This method mirrors the physical process of molecular aggregates forming in liquid solutions: aggregates are generated in the most probable processes of inelastic multiple binary collisions between polymethine species generally differing in complexity. The results obtained are given against a background of the theoretical results on the shape of optical bands in polymethine dyes and their aggregates (dimers, H*- and J-aggregates) previously obtained by V.V.E.

Structure-property relationship of D-A type copolymers based on thienylenevinylene for organic electronics

A series of D-A type conjugated polymers based on (E)-1,2-bis(3-dodecyllthiophen-2-yl)ethene (TV) as electron donor unit and with different repeating subunits, PTVBO8, PTVBT8, PTVTBO12, and PTVTBT12 were synthesized for use in organic field effect transistors and bulk heterojunction organic photovoltaics. Upon incorporation of alkoxy substituents in acceptor units, benzooxadiazole (BO) and benzothiadiazole (BT), polymer solubility improved and higher molecular weight polymers were obtained. In addition, all copolymers showed favorable thermal stability (Td > 300 °C), and low band gap properties (1.49–1.67 eV). The thiophene-flanked TV-TBX copolymers, PTVTBO12 and PTVTBT12, exhibited higher molecular weight and superior device performance in both OFETs and OPVs compared with the TV-BX copolymers. The electronic energy levels of copolymers were strongly influenced by the nature of acceptor units, while optical band gaps and shape of molecular orientation of polymer chains were affected by the presence or absence of thiophene spacer. Charge carrier mobilities in TV-TBX copolymers were 1 order of magnitude greater than in TV-BX copolymers. OFETs based on a PTVTBT12 with TG/BC configuration displayed the highest hole mobility of 0.48 cm2 V−1 s−1. The photovoltaic device containing a PTVTBO12:PC71BM (1:2 w/w) blend system exhibited best performance with a Voc of 0.56 V, a short-circuit current density (Jsc) of 13.1 mA cm−2, a fill factor (FF) of 69%, and a power conversion efficiency (PCE) of 5.0%.

Toward fully nonempirical simulations of optical band shapes of molecules in solution: a case study of heterocyclic ketoimine difluoroborates.

This study demonstrates that a hybrid density functional theory/molecular mechanics approach can be successfully combined with time-dependent wavepacket approach to predict the shape of optical bands for molecules in solutions, including vibrational fine structure. A key step in this treatment is the estimation of the inhomogeneous broadening based on the hybrid approach, where the polarization between solute and atomically decomposed solvent is taken into account in a self-consistent manner. The potential of this approach is shown by predicting optical absorption bands for three heterocyclic ketoimine difluoroborates in solution.

Improving the Accuracy of Excited-State Simulations of BODIPY and Aza-BODIPY Dyes with a Joint SOS-CIS(D) and TD-DFT Approach.

BODIPY and aza-BODIPY dyes constitute two key families of organic dyes with applications in both materials science and biology. Previous attempts aiming to obtain accurate theoretical estimates of their optical properties, and in particular of their 0-0 energies, have failed. Here, using time-dependent density functional theory (TD-DFT), configuration interaction singles with a double correction [CIS(D)], and its scaled-opposite-spin variant [SOS-CIS(D)], we have determined the 0-0 energies as well as the vibronic shapes of both the absorption and emission bands of a large set of fluoroborates. Indeed, we have selected 47 BODIPY and 4 aza-BODIPY dyes presenting diverse chemical structures. TD-DFT yields a rather large mean signed error between the experimental and theoretical 0-0 energies with a systematic overshooting of the transition energies (by ca. 0.4 eV). This error is reduced to ca. 0.2 [0.1] eV when the TD-DFT 0-0 energies are corrected with vertical CIS(D) [SOS-CIS(D)] energies. For BODIPY and aza-BODIPY dyes, both CIS(D) and SOS-CIS(D) clearly outperform TD-DFT. The present computational protocol allows accurate data to be obtained for the most relevant properties, that is, 0-0 energies and optical band shapes.

Efficient and automatic calculation of optical band shapes and resonance Raman spectra for larger molecules within the independent mode displaced harmonic oscillator model

In this work, an improved method for the efficient automatic simulation of optical band shapes and resonance Raman (rR) intensities within the "independent mode displaced harmonic oscillator" is described. Despite the relative simplicity of this model, it is able to account for the intensity distribution in absorption (ABS), fluorescence, and rR spectra corresponding to strongly dipole allowed electronic transitions with high accuracy. In order to include temperature-induced effects, we propose a simple extension of the time dependent wavepacket formalism developed by Heller which enables one to derive analytical expressions for the intensities of hot bands in ABS and rR spectra from the dependence of the wavepacket evolution on its initial coordinate. We have also greatly optimized the computational procedures for numerical integration of complicated oscillating integrals. This is important for efficient simulations of higher-order rR spectra and excitation profiles, as well as for the fitting of experimental spectra of large molecules. In particular, the multimode damping mechanism is taken into account for efficient reduction of the upper time limit in the numerical integration. Excited state energy gradient as well as excited state geometry optimization calculations are employed in order to determine excited state dimensionless normal coordinate displacements. The gradient techniques are highly cost-effective provided that analytical excited state derivatives with respect to nuclear displacements are available. Through comparison with experimental spectra of some representative molecules, we illustrate that the gradient techniques can even outperform the geometry optimization method if the harmonic approximation becomes inadequate.

Influence of Temperature and Pressure on Shape and Shift of Impurity Optical Bands in Polymer Glasses

The shape, broadening, and shift of optical absorption spectra of molecular impurity centers in polymer glasses are considered in terms of inhomogeneous energy distributions and coupling of electronic transitions to vibrations. Persistent spectral hole burning was applied for frequency-selective probing of zero-phonon lines. The shift and broadening of spectral holes were studied between 5 and 50 K and by applying a hydrostatic He gas pressure up to 200 bar. Broadband absorption spectra were recorded between 5 and 300 K in poly(methyl methacrylate) and polyethylene. In addition to "normal" thermal broadening, due to the first- and second-order electron phonon coupling, several narrowing components were predicted on the basis of frequency dependent hole behavior. Thermal expansion of the matrix and the relaxation of local strains, previously accumulated on cooling below the glass temperature can lead to shrinking of the inhomogeneous width. A Voigt treatment of absorption band shapes reveals that the Gaussian component can indeed suffer remarkable narrowing. Inhomogeneous band shapes and the frequency-dependent thermal and baric line shifts were rationalized with the aid of a pair of two-body Lennard-Jones potentials. The shift of potential well minima is a crucial factor influencing solvent shifts, inhomogeneous band shapes, pressure shift coefficients, and quadratic electron phonon coupling constants.

Pressure Effect on the Optical Bandshape of Solid Oxygen

The magnetism in solid oxygen, especially in different high-pressure phases, is not completely understood but can be studied indirectly by spectroscopic techniques. Therefore, we measured and modeled pressure effects on the optical band shape of vibronic two-molecule transitions 3 3 → 1Δg3 . Corresponding spectra at ambient and elevated (P < 10 GPa) hydrostatic pressure and low temperature were very complex but could be clearly assigned to a zero phonon line (ZPL), which in solid oxygen is presented by the exciton−magnon doublet, and its phonon sideband. After the deconvolution of the spectra (ZPL and sideband), the frequency and integrated intensity of the band origin were plotted as functions of pressure. We tried to develop a theory and to model the combined excitation (exciton + magnon + phonons); then we could derive theoretical relations that we compared to experimental data: (i) the splitting of the exciton−magnon doublet increases with pressure because of the growth of all (resonance and exchange) interactions in the basal ab-plane; (ii) the integrated intensity of the ZPL decreases with pressure because the equilibrium positions of molecular oscillators in the ground and optically excited crystal states are shifted relative to each other; (iii) the total band intensity increases with pressure as the combined excitations are assisted by intermolecular exchange interaction due to the decrease in the distance between molecules participating in this transition.

A theoretical study of the effect of disorder of the transition dipole moments of molecules on the shape of optical bands of molecular aggregates

Aggregates with substitutional disorder, in which molecules of different types have different transition dipole moments, are considered. The relations between the absorption spectra of aggregates with disordered and nondisordered transition dipole moments are obtained for two limiting cases: (1) the case when there is no statistical correlation between the transition energies and transition dipole moments of the molecules and (2) the case of total correlation, when the transition energies and transition dipole moments are strictly related to each other. For aggregates that are characterized by substitutional disorder along with diagonal disorder, an effective method of calculation of the optical bands is developed. Numerical calculations of the absorption bands of aggregates consisting of molecules of two types are carried out at different values of the parameters.

Absorption spectrum of Ge-doped silica samples and fiber preforms in the vacuum ultraviolet region

We report absorption measurements in the vacuum ultraviolet (VUV) spectral region on Ge-doped silica samples grown through chemical vapor deposition (CVD) and fiber preforms grown through modified chemical vapor deposition (MCVD) with GeO 2 doping concentration from 0.3 to 4.0 mol%. We observed in all spectra an absorption band at 5.15 eV and a structure at about 7.0 eV. We observed differences in the absorption spectrum between Ge-doped silica samples and fiber preforms in the shape and relative amplitude of optical absorption bands. The intensity of defect-related bands depends on the Ge concentration and distribution. Differences in Ge concentration and distribution are due to the preparation methods and growing conditions.

Mathematical modeling of spectral selective absorption and reflection of light by metal-dielectric composites

Metal-dielectric absorbing composite coatings are widely used in solar cell elements, as ‘black’ coatings in optical instruments. An approach to theoretical evaluation of spectral dependent absorption and Fresnel reflection coefficients for a concentrated system of absorbing spherical metal particles imbedded in a dielectric matrix is presented. The approach is based on the renormalized cluster expansion for the dielectric function of a disordered system of strongly absorbing dipole scatterers. Dipole—dipole interaction depending on the particle concentration are taken into account. The calculation procedure predicts optical behavior of particulate metal composite coatings on glass. As an example of the use of the method calculated spectra of the absorption and Fresnel reflection coefficients for silver and copper particle systems in a transparent dielectric matrix are presented. Changes of the position, the intensity and the shape of optical absorption spectral bands due to concentration effects and formation of shells around metal particles are discussed.

Effect of intermolecular vibronic coupling on nonradiative transitions and optical absorption of dimers

The theory of intermolecular vibronic coupling of dimers is considered. It will be shown that even small intermolecular interaction has significant effect on nonradiative lifetime and optical absorption band shape of dimers. Results of calculations are compared to experimental data on optical absorption and nonradiative lifetime of Mg-methyl bacteri-opheophorbide-d dimers.

Electron transfer optical bands of charge-ordered mixed valence compounds. Quasidynamical model

An approximate quasidynamical model is proposed to describe electron transfer bands of mixed-valence charge-ordered crystals. Within the scope of this model the adiabatic approximation is employed for order parameter calculation. The dynamical (quantum-mechanical) single-cluster problem is solved in the molecular field approach. The electron-transfer (intervalance) optical band shape is investigated in detail for different phase states of a mixed-valence crystal. Intervalence absorption band shape and position provide important data on key parameters of mixed-valence cystals, i.e. double exchange, vibronic and intercluster interaction parameters. Comparison of results obtained for the semiclassical and quasidynamical models is presented for different values of vibronic coupling, double exchange and intercluster interaction. The semiclassical approximation is shown to be not applicable for the description of some important spectral regions of intervalence bands.

Disorder and the non-radiative decay of Cr3+-doped glasses

This paper describes experimental studies of the distribution of crystal field sites occupied by Cr3+ ions in different glasses. The effects of this site-to-site disorder on the optical band shape of 4T2 ↔ 4A2 and 2E ↔ 4A2 transitio ns and their temperature dependences are calculated, on the assumption that the disorder distribution function is a Gaussian and compared with experimental results.

Optical characterization of tunable solid-state laser gain media

The transition metal ions are optical centres that promise tunable laser operation at room temperature over much of the visible and near-infrared regions. This review presents the essential characteristics used in optical assessment of possible laser-active solids and some of the theory required to understand the experimental results. Also presented is a survey of the main features of the optical absorption-emission cycle, luminescence decay profiles, optical bandshapes and excited-state absorption for Ti3+, Cr3+ and Co2+ ions in (essentially) octahedral environments. Finally, materials characteristics (for example, radiative against non-radiative decay, excited-state absorption and disorder) that limit laser performance are discussed.