Optical Absorption Behavior Research Articles

Optical properties of gapped graphene structure in the presence of electron-phonon interaction: A full band approach

We compute the optical conductivity of gapped graphene taking into account the effects of interaction between electrons and Einstein phonons beyond the usual Dirac-cone approximation. Our study is based on the Kubo formula that is established upon the retarded self-energy. Specially we report the frequency dependence of optical absorption of the structure. We find numerical results for frequency dependence of optical absorption for different values of gap parameter in the presence of Holstein phonons. We have also studied the effects of electron-phonon coupling strength and electronic concentration on the behavior of optical absorption of the gapped graphene structure. Our results show the increase of electronic chemical potential in doped case leads to appear optical band gap in the structure. This optical gap arises from Pauli blocking of vertical transitions when conduction band is doped. Electron-phonon coupling broadens the peak in the optical spectral and decreases the intensity of optical absorption. However the frequency position of the peak is not considerably affected by electron-phonon coupling.

Crystal growth, vibrational, optical, thermal and theoretical studies of a nonlinear optical material: 2-Methyl 3,5-dinitrobenzoic acid

Single crystals of 2-methyl 3,5-dinitro benzoic acid with reasonable size have been grown by slow evaporation solution growth method using ethanol as solvent. Quantum chemical calculation of 2-methyl 3,5-Dinitro benzoic acid was carried out by using DFT/B3LYP/6-31+G(d,p) method. The powder X-ray diffraction pattern was recorded and indexed. Both the experimental and theoretical vibrational spectrum validates the presence of functional groups. Polarizability, first order hyperpolarizability and the electric dipole moment values have been computed theoretically. The 1H and 13C NMR chemical shift of the molecule was calculated and compared with experimental results. TG/DSC analysis has been employed to understand the thermal and physio-chemical stability of the title compound. Frequency conversion property of the crystal was tested by Kurtz and Perry method. Optical absorption behavior of the grown crystal was examined by recording the optical spectrum and band gap energy was also estimated. The calculated HOMO and LUMO energy shows the charge transfer nature of the molecule.

Fluorescence emission properties of rhodamine B encapsulated organic-inorganic hybrid mesoporous silica host

Mesoporous silica material can be viewed as an ideal solid host for constructing desirable dye laser with tunable wavelength range. In this investigation, Rhodamine B molecules were successfully encapsulated into the pore of highly ordered MCM-41 and Phenyl-functionalized MCM-41 mesoporous silica by using a simple and facile postgrafting method. The as-gained Rhodamine B encapsulated mesoporous silica materials were successfully characterized by Fourier transform infrared spectroscopy, nitrogen adsorption-desorption and small angle X-ray diffraction. Particularly, the optical absorption and electrochemical behaviors investigated by UV-vis absorption spectra and electrochemical cyclic voltammogram indicate that the difference on the hydrophillic nature of different mesoporous silica hosts has great influence on the existence state of Rh B molecules, resulting lead to strong fluorescence and obvious blue-shift of the encapsulated Rhodamine B molecules in the proposed organic-inorganic hybrid mesoporous. Furthermore, it was pointed out that the significant host-guest interactions of mesoporous silica and Rhodamine B are related not only to the structure, but also to the environmental and surrounding polarity of the materials.

Evaluation of Nanostructure, optical absorption, and thermal behavior of poly(vinyl alcohol)/poly (N‐vinyl‐2‐pyrrolidone) based nanocomposite films containing coated SiO2 nanoparticles with citric acid and l(+)‐ascorbic acid

Nanocomposite films of poly(vinyl alcohol) (PVA)–poly(N‐vinyl‐2‐pyrrolidone) (PVP) blend filled with different weight percentages of nano‐silica were prepared using solution intercalation method. At first, to better dispersion and good compatibility of nano‐silica embedded in the polymer matrix, surface tailoring of it was carried out by two bio‐safe molecules, citric acid and l(+)‐ascorbic acid. Then, the effect of the modified nano‐silica (MS) on the PVA–PVP blend was studied. So, different characterization techniques were running including, Fourier transform infrared (FT‐IR) spectroscopy, X‐ray diffraction analysis (XRD), field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), ultraviolet–visible (UV–Vis) spectroscopy, and thermogravimetric analysis (TGA). POLYM. COMPOS., 39:2012–2018, 2018. © 2016 Society of Plastics Engineers

Study of nonlinear optical absorption properties of V2O5 nanoparticles in the femtosecond excitation regime

In this work, we report for the first time, the nonlinear optical absorption properties of vanadium pentoxide (V2O5) nanoparticles in the femtosecond excitation regime. V2O5 nanoparticles were synthesized through solution combustion technique. The as-synthesized samples were further characterized using XRD, FESEM, EDAX, TEM and UV–visible spectroscopy. X-ray diffraction results revealed the crystalline nature of the nanoparticles. Electron microscopy studies showed the size of the nanoparticles to be ~200 nm. Open-aperture z-scan technique was employed to study the nonlinear optical absorption behavior of the synthesized samples using a 100-fs laser pulses at 800 nm from a regeneratively amplified Ti: sapphire laser. The mechanism of nonlinear absorption was found to be a three-photon absorption process which was explained using the density of states of V2O5 obtained using density functional theory. These nanoparticles exhibit strong intensity-dependent nonlinear optical absorption and hence could be considered for optical-power-limiting applications.

Facile synthesis of sulfate-doped Ag3PO4 with enhanced visible light photocatalystic activity

Sulfate-doped Ag3PO4 photocatalysts were successfully synthesized via a simple precipitation method. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed that SO42− ions were incorporated into the lattice of Ag3PO4 by replacing PO43−. The crystalline structure and optical absorption behavior of Ag3PO4 remain unchanged after SO42− doping. However, SO42−-doped Ag3PO4 catalyst with 0.50 at% SO42− concentration ratio exhibited remarkably enhanced photocatalytic activity, and completely decomposed rhodamine B (RhB) and methylene blue (MB) in 4 and 5min under visible light irradiation, respectively. Its degradation rate constant was more than 5 times higher than that of pristine Ag3PO4. The high photocatalytic performance is attributed to the fact that doping SO42− into Ag3PO4 lattice can improve the separation efficiency of photogenerated electron-hole pairs and hinder their recombination. In addition, the results of density functional theory (DFT) calculations indicate that SO42− substitution can effectively tune the electronic structures of Ag3PO4, thus resulting in high photocatalytic activity under visible light irradiation.

Improved nonlinear optical and optical limiting properties in non-covalent functionalized reduced graphene oxide/silver nanoparticle (NF-RGO/Ag-NPs) hybrid

Nonlinear optical (NLO) response under near infrared (800 nm) and visible (532 nm) laser excitations, of 100 fs (fs) and 5 ns (ns) pulse durations respectively, of reduced graphene oxide (RGO), non-covalent functionalized reduced graphene oxide (NF-RGO) and NF-RGO decorated with various concentration of silver nanoparticles (NF-RGO/Ag-NPs) have been investigated using the Open-aperture Z-Scan technique. For both femtosecond and nanosecond laser excitations, the studied graphene-based materials exhibit good nonlinear optical power limiting properties (OL), with NF-RGO/Ag-NPs sample prepared with 0.1 M AgNO3 showing the best nonlinear optical properties. For the ns regime, the optical limiting threshold decreased from 8.3 J/cm2 in NF-RGO to 4.3 J/cm2 in NF-RGO/Ag-NPs, while at fs regime, the nonlinear absorption coefficient (β) was found to increase with decrease in concentration of Ag-NPs in the hybrid. Two-photon absorption (2 PA) in combination with saturable absorption (SA) in femtosecond regime, and reverse saturable absorption (RSA) along with saturable absorption (SA) in the nanosecond regime, are responsible for the observed nonlinear optical absorption (NLA) behavior in these materials. These findings show that the as-synthesized NF-RGO/Ag-NPs hybrid is a relatively better material for nonlinear optical limiting applications.

Fe-substituted Co-Li bismuth borate glasses

Cobalt lithium bismuth borate glasses substituted with different amounts of iron in the compositional range of xFe2O3·(20 − x)CoO·30Li2O·10Bi2O3·40B2O3 (x = 0, 5, 10, 15 and 20 mol%) have been synthesized via melt quench route. The synthesized glasses are investigated for their crystallization kinetics behavior through non-isothermal differential scanning calorimetry (DSC) measurements and their optical absorption behavior through UV–Vis spectroscopic measurements. Thermal activation energies corresponding to the crystallization and glass transition properties are evaluated and reported. The variation in the characteristic temperatures (glass transition temperature, crystallization temperature and melting temperature) with change in heating rate and change in the composition of iron oxide is discussed. The optical absorption results are analyzed to evaluate the optical band gaps corresponding to indirect allowed and forbidden Mott transition. The band tailing parameter (B) corresponding to each Mott transition has also been evaluated and reported. The Urbach’s (ΔE) energy is calculated by analyzing the fundamental absorption edge, and the obtained results are reported.

Strain- and twist-engineered optical absorption of few-layer black phosphorus

Density functional and many-body perturbation theories calculations were carried out to investigate fundamental and optical bandgap, exciton binding energy and optical absorption property of normal and strain- and twist-engineered few-layer black phosphorus (BP). We found that the fundamental bandgaps of few layer BP can be engineered by layer stacking and in-plane strain, with linear relationships to their associated exciton binding energies. The strain-dependent optical absorption behaviors are also anisotropic that the position of the first absorption peak monotonically blue-shifts as the strain applies to either direction for incident light polarized along the armchair direction, but this is not the case for that along the zigzag direction. Given those striking properties, we proposed two prototype devices for building potentially more balanced light absorbers and light filter passes, which promotes further applications and investigations of BP in nanoelectronics and optoelectronics.

Growth, thermal, vibrational studies and quantum chemical calculations of 2,6-dibromo-4-nitrophenol: a new nonlinear optical crystal

Good-quality single crystals of 2,6-dibromo-4-nitrophenol have been grown by slow evaporation solution growth technique using ethanol as solvent. The lattice parameters of the grown crystal were confirmed from single-crystal XRD analysis. Quantum chemical calculations were carried out using DFT /B3LYP/6-31 G(d,p) method. The optimized geometrical parameters have been obtained from the computational technique, and the result shows good agreement with the experimental XRD data. Both the experimental and theoretical vibrational spectrum confirms the presence of functional groups. Optical absorption behaviour of the grown crystal was examined by recording the optical spectrum and band gap energy was also estimated. Theoretical investigation shows that the title compound exhibits non-zero first-order hyperpolarizability values and has microscopic non-linear optical behaviour which is 22 times more than that of urea. The calculated HOMO and LUMO energies reveal the charge transfer characteristic of the title compound. Frequency conversion property of the grown crystal was investigated using Kurtz and Perry powder technique.

An organic dye-polymer (phenol red-poly (vinyl alcohol)) composite architecture towards tunable -optical and -saturable absorption characteristics

Herein, we demonstrate that blending an organic dye (guest/filler), with a vinyl polymer (host template), is an inexpensive and simple approach for the fabrication of multifunctional photonic materials which could display an enhancement in the desirable properties of the constituent materials and, at the same time provide novel synergistic properties for the guest-host system. A new guest-host nanocomposite system comprising Phenol Red dye and poly (vinyl alcohol) as guest and host template, respectively, which exhibits tunable optical characteristics and saturable absorption behavior, is introduced. The dependence of local electronic environment provided by the polymer template and the interactions of the polymer molecules with the encapsulated guest molecules on the observed optical/nonlinear absorption behavior is discussed. An understanding of the tunability of the optical/ photophysical processes, with respect to the filler content, as discussed herein could help in the design of improved optical materials for several photonic device applications like organic light emitting diodes and saturable absorbers.

Oriented rutile TiO2 nanorod arrays for efficient quantum dot-sensitized solar cells with extremely high open-circuit voltage

TiO2 nanoparticles are typically employed to construct the porous films for quantum dot-sensitized solar cells (QDSCs). However, undesirable interface charge recombination at grain boundaries would hinder the efficient electron transport to the conducting substrate, giving rise to the decline of open-circuit voltage (Voc). In this work, vertically aligned architectures of oriented one-dimensional (1D) TiO2 nanorod arrays hydrothermally grown on substrates pave a way in designing highly efficient QDSCs with efficient radial-directional charge transport. SEM, TEM, XRD, and Raman spectroscopy were employed to characterize the as-prepared TiO2 nanorods, showing the rutile phase with single-crystalline structure. The homogeneous deposition of CdS/CdSe QDs on the surface of TiO2 nanorods has been achieved by in-situ grown strategies (i.e., successive ionic layer absorption and reaction, and chemical bath deposition). An extremely high Voc value up to 0.77V has been achieved for CdS/CdSe QDSCs based on the well-ordered 1D nanorod arrays. To the best of our knowledge, it is the highest Voc reported for TiO2-based QDSCs. Dependencies of photovoltaic performance, optical absorption, and interfacial charge behavior on the length of nanorods were systematically investigated. A 1.7μm nanorod-array photoelectrode-based QDSC delivers a remarkable power conversion efficiency up to 3.57% under simulated AM 1.5 100mWcm−2 illumination, attributed to the balance of competition between the increase of QD loading and suppression of interfacial recombination. This work highlights the combination of QDs with high absorption coefficient 1D architectures possessing efficient charge transport for constructing high efficiency solar cells.

Modification of morphological, mechanical, optical and thermal properties in polycaprolactone-based nanocomposites by the incorporation of diacid-modified ZnO nanoparticles

In this paper, nanocomposite (NC) films of polycaprolactone (PCL)/ZnO-DA were prepared by casting/solvent evaporation method. For this purpose, ZnO nanoparticles were first modified with diacid (DA) based on bioactive amino acid (N-trimellitylimido-l-alanine), at room temperature using methanol as solvent and ultrasound irradiation method. Then, PCL/ZnO-DA NCs were obtained by addition of various weight percentages (2, 4, and 6 wt%) of ZnO-DA into the PCL matrix, under vigorous stirring and subsequent ultrasonic irradiation. The structural characterization of the NC films was carried out using Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. It was found that relative changes in the peaks and morphology were observed, as the concentration of filler was increased. In addition, embedding the NPs into PCL exhibited a reduction in thermal stability of NCs as compared to the pure PCL. FE-SEM and TEM morphological analysis did not show any aggregation of the NPs in the prepared NCs. It was also found that chemical composition of NC films had influenced their optical absorption and mechanical behaviors.

Influence of thermally induced structural and morphological changes, and UV irradiation on photoluminescence and optical absorption behavior of CdS nanoparticles

Polycrystalline cubic CdS nanoparticles (NPs) with a crystallite size () ~3 nm were synthesized by chemical precipitation method at room temperature. Thermal induced structural and morphological changes have been investigated using x-ray diffraction, high-resolution transmission electron microscope, x-ray fluorescence, Fourier transform infrared and Raman spectroscopy. The influence of these changes on optical absorption and photoluminescence (PL) characteristics have been studied. It was found that increasing annealing temperature (Ta), results in structural phase transitions at 300 and 700 °C, increasing and red shift of the optical band gap () due to the improvement in crystallinity. The photoluminescence emission spectrum of nonstoichiometric CdS (Cd-rich) nanopowder reveals emission bands at 365, 397, and 434 nm. Furthermore, PL spectrum of colloidal solution exhibits additional green and red emission bands at 535, 570 and 622 nm. To explain the mechanism of PL emission in CdS NPs, trapping and radiative recombination levels have been identified and the corresponding energy band diagrams are suggested. Annealing process results in an overall enhancement in PL intensity due to the improvement in crystallinity associated with the reduction of nonradiative surface state defects. Irradiation of CdS NPs colloidal solution at UV irradiation dose <13 J cm−2 leads to the enhancement of PL quantum efficiency and blue shift of (i.e. photo-brightening) due to the decrease in the particle size deduced from Brus equation , This behavior is due to UV irradiation effects such as photopolymerization, the formation of CdSO4 passivation layers due to photooxidation and the reduction in by photocorrosion process. At UV irradiation dose <13 J cm−2, PL emission intensity continuously enhances without any change in both and . This behavior is discussed in terms of electron filling model. Boltzmann curve fitting successfully describes the dependence of both and on UV irradiation dose.

Synthesis, characterization, structural and optical absorption behavior of SnxSbySz powders

The SnSb4S7, SnSb2S4, Sn4Sb6S13, Sn2Sb2S5 and Sn3Sb2S6 materials were synthesized by the Bridgmann technique. The five pellets were characterized by X-ray diffraction, Raman spectroscopy and diffuse reflectance spectroscopy. The changes observed in Raman spectra were due to the influence of the composition. Kubelka–Munk model and inversion method were used to determine the band gap energies of the samples. The absorption edges were determined using the first derivative of diffuse reflectance spectra. The band gap varies between 1.17 and 1.06eV.

Synthesis, surface properties and optical characteristics of CuV2O6 nanofibers

In3+-doped CuV2O6 nanofibers were prepared via the hydrothermal synthesis method, which produced fibers with a typical diameter of 100 nm, and a length of 1–5 μm. The nanofibers grew in a preferred [020] direction. The crystal phase together with the structure was studied via X-ray polycrystalline diffraction (XRD) and the Rietveld refinement. The surface characteristics of this nanostructure were measured with a scanning electron microscope (SEM), energy dispersive spectra (EDS), transmission electron microscopy (TEM), and N2–adsorption–desorption isotherms. Photo-activities were evaluated by optical absorption, luminescence, and decay behaviors. The band-gap structures and positions were investigated. The vanadate has an efficient optical absorption from the UV to the visible wavelength region with an indirect allowed transition characterized by the narrow gap energy of 1.96 eV. The photocatalysis was investigated by the photo-degradation of RhB solutions irradiated by visible light. Correspondingly, CuV2O6:In3+ nanofibers possess quenched luminescence and have a more efficient photocatalytic activity on the RhB degradation. Photocatalytic mechanisms were proposed based on the experimental results, the band-energy positions, and the trapping experiments. The coexistence of V4+/V5+ ions and induced-color centers was discussed on the proposed photocatalytic mechanism. The results demonstrated the promising potency of such In3+-doped CuV2O6 nanofibers for technological applications due to their high photo-activity and good cycling performance with the fiber morphology.

Optical observation of different conformational isomers in rubrene ultra-thin molecular films on epitaxial graphene

Optical differential reflectance spectroscopy in combination with low-energy electron diffraction and scanning tunneling microscopy is used to investigate (ultra-)thin rubrene films grown on epitaxial graphene. The optical absorption behavior is compared to thin films on graphite(0001), muscovite mica(0001), and amorphous glass. All the optical spectra can be explained by the presence of two different spectral components, namely a high-energy and a low-energy component. We assign these two optical species to two different conformations of the rubrene molecule.

Optical visualization and polarized light absorption of the single-wall carbon nanotube to verify intrinsic thermal applications

The predicted extraordinary properties of carbon nanotubes (CNTs) from theoretical calculations have great potential for many applications. However, reliable experimental determination of intrinsic properties at the single-tube level is currently a matter of concern, and many challenges remain because of the unhandled and nanoscale size of individual nanotubes. Here, we demonstrated a prototype to detect the intrinsic thermal conductivity of the single-wall carbon nanotube (SWCNT) and verify the significant non-resonant optical absorption behavior on tiny nanotubes by integrating the nanotube and ice into a new core-shell design. In particular, a reversible optical visualization method based on the individual suspended ultra-long SWCNT was first developed by wrapping a nanotube with ice in the cryogenic air environment. The light-induced thermal effect on the hybrid core-shell structure was used to melt the ice shell, which subsequently acted as a temperature sensor to verify the intrinsic thermal conductivity of the core-like nanotube. More interestingly, we successfully determined for the first time the thermal response phenomenon of the tiny absorption cross section in SWCNT in the vertical-polarization configuration and the significant non-resonant absorption behavior in the parallel-polarization configuration. These investigations will provide a better understanding for the unique optical behaviors of CNT and enable the detection of intrinsic properties of various one-dimensional nanostructures such as nanotubes, nanowires, and nanoribbons. Growing ice on a carbon nanotube not only enables the nanotube to be optically imaged but also permits its thermal properties to be measured. Isolated single-walled carbon nanotubes with diameters of just a few nanometres are usually impossible to observe using an optical microscope. Now, Xiao Zhang and other scientists in China have discovered a non-destructive and reversible way to optically observe carbon nanotubes and measure their thermal properties. Their method involves growing a few-micrometre-thick layer of ice on a suspended nanotube by placing it in a cryogenic environment. The researchers then melted the ice by irradiating the ice-coated nanotube with a laser beam, while inferring the nanotube s temperature from a shift in its Raman signal. From this information, they could determine the intrinsic thermal conductivity and the light absorption behavior of the nanotube.

Crystallization kinetics, optical and dielectric properties of Li2O⋅CdO⋅Bi2O3⋅SiO2 glasses

Crystallization kinetics, optical absorption and electrical behavior of lithium cadmium silicate glasses with different amount of bismuth oxide were investigated using non-isothermal crystallization approach, UV–VIS–NIR spectroscopy and impedance spectroscopy, respectively. These glasses were synthesized by normal melt quenching technique. Variation in physical properties, viz. density, molar volume with Bi2O3:SiO2 ratio were related to the structural changes occurring in the glasses. The glass transition temperature (Tg), crystalline peak temperature (Tp) and melting temperature (Tm) of these glasses were determined using differential scanning calorimeter at various heating rates. The dependence of Tg and Tp on heating rate has been used for the determination of the activation energy of glass transition and crystallization. Thermal stability parameters have revealed high stability of the glass prepared with 40mol% of Bi2O3 content. The crystallization kinetics for the glasses was studied by using the Kissinger and modified Ozawa equations. Appearance of a sharp cut-off and a wide and reasonable transmission in VIS–NIR region makes these glasses suitable for IR transmission window. The cut-off wavelength, optical band gap and Urbach’s energy have been analyzed and discussed in terms of changes in the glass structure. By analyzing the impedance spectra, the ac and dc conductivities, activation energy for dc conduction (Edc) and for relaxation (EM″) were calculated. The results obtained from dc conductivity confirm the network forming role of Cd2+ ion in the glasses. The scaling of the conductivity spectra has been used to interpret the temperature dependence of the relaxation dynamics. The observed conductivity spectra follows power law with exponent ‘s’ which decreases with temperature and satisfies the correlated barrier hopping (CBH) model. The perfect overlying of normalized plots of electrical modulus on a single ‘master curve’ depicts temperature as well as composition independent dynamical process at several frequencies.

Synthesis, characterization and optical properties of in situ ZnFe2O4 functionalized rGO nano hybrids through modified solvothermal approach

Graphene, honeycomb structure of carbon having exceptional characteristics have attracted researcher’s interest and is now being studied and used in numerous technological areas and next generation nano devices. In this research work, reduced graphene oxide was functionalized with magnetic nano crystals, i.e. ZnFe2O4 via modified solvothermal approach. X-ray diffraction and Micro Raman spectroscopy was used to confirm structural aspects of synthesized graphene oxide and ZnFe2O4 pristine magnetic nano crystals and the functionalized rGO-ZnFe2O4 nano hybrid. Morphology were analyzed through SEM showing that the particles sizes were in between 24 and 27nm range attached to reduced graphene oxide sheets while composition and valence state of functional groups were analyzed through XPS. UV–Vis spectroscopy was carried out for analyzing their optical absorption behavior. Their optical characteristics were explained in depth in relation with their structural aspects and functionalization behavior.