Optical Absorption Band Research Articles

Hyperspectral imaging of lipids in biological tissues using near- and shortwave infrared transmission mode: A pilot study.

Label-free hyperspectral imaging (HSI) of lipids was demonstrated in the near-infrared (NIR) and shortwave infrared (SWIR) regions (950-1800 nm) using porcine tissue. HSI was performed in the transmission light-pass configuration, using a NIR-SWIR camera coupled with a liquid crystal tunable filter (LCTF). The transmittance spectra of the regions of interest (ROIs), which correspond to the lipid and muscle areas in the specimen, were utilized for the spectrum unmixing. The transmittance spectra in ROIs were compared with those recorded by a spectrophotometer using samples of adipose and muscle. The lipid optical absorption bands at 1210 and 1730 nm were first used for the unmixing and mapping. Then, we performed the continuous multiband unmixing over the entire available spectral range, thereby, considering a combination of characteristic absorption bands of lipids, proteins and water. The enhanced protocol demonstrates the best way of distinguishing small adipose inclusions of 1-10 μm size. This article is protected by copyright. All rights reserved.

Thermoluminescence of rose quartz from Minas Gerais, Brazil

This article reports the thermoluminescence (TL) properties of rose quartz from Minas Gerais (Brazil), a translucent pink variety of quartz. Firstly, the sample shows a pure α-quartz phase, based on X-ray diffraction results. Also, the mineral shows a wide optical absorption band at about 500 nm, typical of rose quartz. In addition, X-ray fluorescence showed a high percentage of purity (99.1% of the SiO2), and the inductively coupled plasma optical emission spectrometry (ICP OES) recorded the presence of elements such as Al, Ca, Fe and Ti. The TL measurements were carried out using a commercial Risø TL/OSL reader, model DA-20, equipped with a built in 90Sr/90Y beta source, used to irradiate the sample to different radiation doses (0.01 – 1Gy). The glow curve, measured at a heating rate of 1 K/s, consists of a prominent peak at 355 K followed by other low intensity peaks at higher temperatures. Measurements of the main peak are reproducibility with a coefficient of variation (C.V.) of ∼1.3% and a repeatability of ∼1.8%. Kinetic analysis of the main peak was carried out using experimental methods comprising Tm-Tstop technique, the initial rise method, peak shape estimation and various computational methods (TGCD, TLanal, TLDecoxcel and GlowFit). The peak obeys first order kinetics, with activation energy of 0.86 eV, and a frequency factor of the order of 1011 s−1. Finally, in the dose range studied, the peak shows a sublinear dose response after which supralinearity sets in.

Tuning the UV absorbing ability of CeO2 nanoparticles with F− doping

Ultraviolet (UV) absorbing material is the key to achieving high performance UV shielding device. Because of the large absorption ability on UV light and excellent long-term stability under UV irradiation, CeO2 nanoparticle is considered potential UV absorber for practical applications. However, the CeO2 related materials still face challenges since its UV absorbing capability is non-adjustable, which is unable to meet the changing requirement. In this work, we obtain serial CeO2 nanoparticles with tunable UV absorbing ability through F− doping. Using un-doped CeO2 nanoparticles with size of about 6 nm as starting material and trifluoroacetic acid as F− source, serial F− doped CeO2 marked as CeO2:F1, CeO2:F2, CeO2:F3 and CeO2:F4 are obtained through a post- fluorination strategy. The F− doping rarely changes the size of CeO2, but obviously changes the optical absorbing ability. As the F− content increases, the optical absorption band of the F− doped nanoparticles gradually shifts to short wavelength. Because of the highest F− content, CeO2:F4 sample displays the greatest blue shift with an absorption band of 345 nm. Calculation result reveals that the introduction of F− enlarges the energy band gap of CeO2, leading to the blue shift of the UV absorption band. Finally, serial coated glasses with tunable UV shielding ability are prepared. Using CeO2 nanoparticles or F− doped CeO2 nanoparticles as UV absorber, the optical absorption band of coated glasses could be tuned between 380 nm and 345 nm.

Core and Shell Contributions to the Phonon Spectra of CdTe/CdS Quantum Dots

The parameters of the shell and interface in semiconductor core/shell nanocrystals (NCs) are determinant for their optical properties and charge transfer but are challenging to be studied. Raman spectroscopy was shown earlier to be a suitable informative probe of the core/shell structure. Here, we report the results of a spectroscopic study of CdTe NCs synthesized by a facile route in water, using thioglycolic acid (TGA) as a stabilizer. Both core-level X-ray photoelectron (XPS) and vibrational (Raman and infrared) spectra show that using thiol during the synthesis results in the formation of a CdS shell around the CdTe core NCs. Even though the spectral positions of the optical absorption and photoluminescence bands of such NCs are determined by the CdTe core, the far-infrared absorption and resonant Raman scattering spectra are dominated by the vibrations related with the shell. The physical mechanism of the observed effect is discussed and opposed to the results reported before for thiol-free CdTe Ns as well as CdSe/CdS and CdSe/ZnS core/shell NC systems, where the core phonons were clearly detected under similar experimental conditions.

Charge transfer effect: a new assignment of the abnormal optical absorption band of gold nanoparticles

As a significant accompanying phenomenon of surface-enhanced Raman scattering (SERS), the addition of foreign molecules to colloidal gold or silver nanoparticles results in a new abnormal optical absorption (AOA) band, which usually appears in the long-wavelength region. The assignment of this AOA band has long been debated as an important issue that is desired to be addressed in the SERS field, which is crucial for a clear understanding of the SERS enhancement mechanism and beneficial to surface plasmonics. In this study, both the calculated and measured optical absorptions of gold nanoparticle monomers and dimers as well as their interactions with adsorbed molecules, showed that the AOA band in the long-wavelength region which was assigned to the characteristic longitudinal localized surface plasmon resonance (LSPR) effect of gold nanoparticle chain aggregates in conventional SERS electromagnetic theory, should be attributed to the charge-transfer resonance absorption from gold nanoparticles to adsorbed molecules. This was further confirmed by the corresponding SERS effects. As the excitation wavelength at 785 nm was resonant with the broad AOA band centered at 750 nm, the SERS peaks of the adsorbed pyridine molecules could be dramatically enhanced due to the charge-transfer resonance effect. In contrast, under an excitation wavelength of 532 nm, the SERS peaks appeared very weak, although the excitation wavelength was resonant with the LSPR absorption band of the individual gold nanoparticles.

A first-principles study of the unsynthesized Indium halide perovskites RbInX3 (X= F, Cl, Br, I) for photovoltaic and photocatalytic applications

Due to their relevant properties, lead-free halide perovskites have attracted wide attention in the scientific community. This study investigates the structural, mechanical, electronic, optical, and photocatalytic properties of the Indium-based halide perovskites RbInX3 (X= F, Cl, Br, I) based on the density functional theory (DFT) using the WIEN2k package. The results show that RbInI3 exhibits a metallic behavior, while RbInBr3, RbInCl3, and RbInF3 exhibit semiconducting behavior with bandgap energies of 0.67, 1.43, and 2.45 eV, respectively. The high optical absorption and corresponding band gap energies make them good candidates for photovoltaic applications. In addition, the RbInF3 compound exhibits good photocatalytic performance since it satisfies the thermodynamic requirements needed to trigger the water-splitting reaction. This study also allows us to analyze the influence of halogen substitution on the properties of the compound RbInX3. Moreover, it will open the way to the experimental community as it is the first to study the properties of these perovskites.

Efficient photocatalytic hydrogen evolution and CO2 reduction by HfSe2/GaAs3 and ZrSe2/GaAs3 heterostructures with direct Z-schemes.

The elaborate configuration of the heterostructure is crucial and challenging to achieve high solar-to-hydrogen efficiency or CO2 reduction efficiency . Here, we predict two heterostructures composed of HfSe2, ZrSe2, and GaAs3 monolayers. The maximum of 42.71%/35.12% with the heterostructures can be reached with the perfect match between the bandgap and band edges. The configurations of the heterostructures are discovered from 12 possible stacking types of the three monolayers. The formation energy, potentials of band edges, carrier mobilities, and optical absorption were used to identify the feasibility of the CO2 reduction reaction (CO2RR), the hydrogen evolution reaction (HER), and the oxygen evolution reaction (OER). The and based on overpotentials and bandgaps and the Gibbs free energies (ΔGs) are evaluated to quantificationally access the photocatalytic performance of the constructed heterostructures. The results demonstrate that high can be obtained for the solar photocatalytic Z-schemes with the HfSe2/GaAs3 and ZrSe2/GaAs3 heterostructures, and these values can be further enhanced through strain engineering. Moreover, small changes in ΔGs were observed for HER, OER, and CO2RR. Therefore, the two heterostructures have excellent performance in photocatalytic hydrogen evolution and CO2 reduction. The results of the electronic properties revealed that the delicate matching of the projected band edges of the monolayers in the heterostructures is responsible for the high photocatalytic performance.

First principles study of electronic and optical properties of S-type heterostructures MoSi<sub>2</sub>N<sub>4</sub>/GeC

In this article, the first principles calculation method is used to study the MoSi<sub>2</sub>N<sub>4</sub>/GeC heterostructures, and calculate its structural, electronic, and optical properties. And the effects of different biaxial strains and vertical electric fields on the band structure and optical absorption characteristics of the heterostructures are also investigated. MoSi<sub>2</sub>N<sub>4</sub>/GeC heterostructure is an indirect bandgap semiconductor with a bandgap of 1.25 eV, with the built-in electric field direction pointing from the GeC layer to the MoSi<sub>2</sub>N<sub>4</sub> layer. In addition, its photogenerated carrier transfer mechanism conforms to the S-type heterostructures mechanism, thus improving the oxidation reduction potential of photocatalytic water decomposition, making it fully meet the requirements of photocatalytic water decomposition with pH = 0–14. Under biaxial strain, the band gap first increases and then decreases with the increase of compressive strain, and the light absorption performance in the ultraviolet region increases with compressive strain increasing. The band gap decreases as tensile strain increases, and the light absorption performance in the visible light region is enhanced in comparison with its counterpart under compressive strain. Under a vertical electric field, the band gap increases with positive electric field increasing, and decreases with negative electric field increasing. In summary, MoSi<sub>2</sub>N<sub>4</sub>/GeC heterostructures can be used as an efficient photocatalytic material in some fields such as optoelectronic devices and photocatalysis.

Энергетический спектр и спектр оптического поглощения экзоэдрального фуллерена С-=SUB=-70-=/SUB=-Br-=SUB=-10-=/SUB=- в модели Хаббарда

Energy spectrum exohedral fullerene С70Br10 with the Cs symmetry groups have been obtained within the Hubbard model and static fluctuation approximation. The energy states have been classified using the methods of group theory, and the allowed transitions in the energy spectra of molecule С70Br10 have been determined. On the basis of the energy spectrum of exohedral fullerene С70Br10 is given an interpretation of experimentally observed optical absorption bands molecule С70Br10.

Энергетический спектр и оптические свойства бромида фуллерена С-=SUB=-70-=/SUB=-Br-=SUB=-10-=/SUB=- в модели Хаббарда

The energy spectrum of molecule C70Br10 of symmetry group Cs were obtained within the Hubbard model in the mean-field approximation. Using group theory methods, the classification of energy states was carried out, and the allowed transitions in the energy spectrum of bromide fullerene C70Br10 of symmetry group Cs were determined. On the basis of this spectrum, an interpretation of experimentally observed optical absorption bands of molecule C70Br10 is proposed.

Energy Spectrum and Optical Absorption Spectra of exohedral Fullerene C-=SUB=-70-=/SUB=-Br-=SUB=-10-=/SUB=- within the Hubbard Model

Energy spectrum exohedral fullerene C70Br10 with the Cs symmetry groups have been obtained within the Hubbard model and static fluctuation approximation. The energy states have been classified using the methods of group theory, and the allowed transitions in the energy spectra of molecule C70Br10 have been determined. On the basis of the energy spectrum of exohedral fullerene C70Br10 is given an interpretation of experimentally observed optical absorption bands molecule C70Br10. Keywords: Hubbard model, Green's functions, energy spectrum, fullerenes, nanosystems, fullerene C70, exohedral fullerene C70Br10.

Gold-nanoparticles induced transition in YVO4 crystal: From saturable to reverse saturable absorption

The embedded gold (Au) nanoparticles (NPs) are synthesized inside the yttrium vanadate (YVO4) crystal by direct Au ion implantation. The formed Au nanospheres are with average diameter of ∼5 nm, generating a clear optical absorption band centered at 595 nm due to the localized surface plasmon resonance (LSPR). With the doping of Au NPs, the nonlinear optical properties of YVO4 crystal are also modified, endowing the substrate with new features. Using femtosecond open-aperture Z-scan investigation under variable laser intensities, the Au NPs-modified YVO4 exhibits saturable absorption (SA) property at moderate excitation irradiances due to the plasmonic effect of embedded Au NPs, whilst transits to reverse saturable absorption (RSA) under higher pump irradiances. As an example for practical applications, we demonstrate a 1-μm pulse laser generation utilizing Au NPs-embedded YVO4 crystal as the saturable absorber. This work suggests that ion beam synthesis of metallic NPs may be a suitable way to tailor properties of functional crystals to achieve diverse applications in optics.

Synergistic effect of covalent functionalization and intrinsic electric field on β-Ga2O3/graphene heterostructures

β-Ga2O3/graphene heterostructure engineering has been regarded as an effective method to improve the optoelectronic performance of the β-Ga2O3 device. Here, hydrogenation/fluorination covalent functionalized graphene (HC/FC) was employed, and the synergistic effect of covalent functionalization and intrinsic electric field (Ein) was introduced to further improve and understand the interfacial properties of the heterostructure. Under the covalent functionalization, type-II band alignment with UV-infrared dual-band absorption was found for β-Ga2O3/HC heterostructure, while reserved type-II band alignment with hole doping was realized for p-type β-Ga2O3/FC heterostructure. Upon introducing the synergistic effect of covalent functionalization and Ein for β-Ga2O3/hydro-fluorinated graphene (HCF) heterostructure, except for the above similar characters, both the band offsets and optical absorption are further enhanced in β-Ga2O3/HCF heterostructures. When the direction of intrinsic Ein points to the contact interface, the Fermi level of β-Ga2O3/F-HCF was much closer to the valence band of β-Ga2O3. It was thought that the synergistic effect of covalent functionalization and Ein was more beneficial to promote the application of p-type β-Ga2O3. These findings were deeply revealed by the band levels, electrostatic potential, and charge transfer introduced. Our results were expected to provide useful insight into the synergistic effect of covalent functionalization and intrinsic Ein as well as to enhance the application potential of β-Ga2O3/graphene-based optoelectronic devices.

Structural, Optical, and Morphological Characterization of Silica Nanoparticles Prepared by Sol-Gel Process

In the current years, silica nanoparticles have become more favorable in various disciplines like medicine, nano-biotechnology, the food industry, and drug delivery due to their tunable physicochemical characteristics. In this paper, the silica nanoparticles were synthesized by hydrolysis and condensation of tetra-ethyl-ortho-silicate (TEOS) in an ethanolic medium using ammonia as a stimulator in the reaction. The chemical bond structures of silica nanoparticles were analyzed by Fourier Transform Infrared Spectroscopy (FT-IR) which confirmed the existence of the Si-O bonds according to the different absorption peaks of the samples. The amorphous structure of these nanoparticles was certified by finding the board peaks in the X-Ray Diffraction (XRD) patterns. The elemental chemical composition of silica nanoparticles was investigated by Energy Dispersive X-Ray Spectroscopy (EDX) where 61.48wt % of silicon and 23.48wt% of oxygen were found. Almost round-shaped spherical and uniform silica nanoparticles with smooth surfaces were investigated by Scanning Electron Microscopy (SEM) measurement. The different particle sizes of silica nanoparticles within the range of 95±5.59 to 280±7.8 nm were found by controlling the concentration of TEOS. The optical absorption spectra and band gap calculations were also analyzed by Ultraviolet-Visible (UV-Vis) spectrophotometry for the different concentrations of TEOS. The results revealed that with increasing the concentration of TEOS, the absorption spectra of silica nanoparticles increased and their optical bandgap decreased from 3.92 eV to 3.79 eV.

Heptazine-Based Ordered-Distorted Copolymers with Enhanced Visible-Light Absorption for Photocatalytic Hydrogen Production.

Poly(heptazine imide) (PHI), one of the attractive allotropes of polymeric carbon nitride, has recently received extensive attention in photocatalysis due to its extended conjugation for fast separation and transfer of the charges. However, pristine PHI bears an intrinsic optical absorption band edge at 460 nm, which largely restrains the visible light utilization. Herein, the narrow-bandgap PHI (N-PHI) with an ordered-distorted interface was fabricated from polycondensation of the mixture of NaSCN, cyanuric chloride, and LiCl. Results revealed that the enhanced optical absorption and the promoted separation and transfer of the charge carriers at the interface greatly improved the photocatalytic performance, which endowed N-PHI with an apparent quantum yield of 20 % for hydrogen production at 450 nm.

Transition-metal ions in β-Ga2O3 crystals: Identification of Ni acceptors

Transition-metal ions (Ni, Cu, and Zn) in β-Ga2O3 crystals form deep acceptor levels in the lower half of the bandgap. In the present study, we characterize the Ni acceptors in a Czochralski-grown crystal and find that their (0/−) level is approximately 1.40 eV above the maximum of the valence band. Both Ni2+ (3d8) and Ni3+ (3d7) acceptors are present in the as-grown crystal. Also present are unintentional Ir3+ (5d6) and Ir4+ (5d5) donors. The neutral Ni3+ acceptors have a low-spin S = 1/2 ground state and are easily monitored with electron paramagnetic resonance (EPR). Principal values of the g matrix for these acceptors are 2.131, 2.138, and 2.233. Although paramagnetic, the singly ionized Ni2+ acceptors are not seen with EPR at X band (9.4 GHz). The Ir4+ donors are monitored with EPR and with infrared absorption spectroscopy. Exposing the Ni-doped β-Ga2O3 crystal to 275 nm light at room temperature increases the concentration of Ni3+ ions and reduces the concentration of Ir4+ ions as electrons move from the acceptors to the donors. After illumination, heating the crystal above 375 °C restores the initial concentrations of the Ni3+ and Ir4+ ions. Broad optical absorption bands peaking near 303 and 442 nm are attributed to the Ni3+ acceptors.

Photothermal property investigation of V2CTx MXene and its use for all-optical modulator

MXenes, as novel two-dimensional materials, have garnered significant attention in the field of lasers and photonics owing to their outstanding electronic and optical properties. The results pertaining to the photothermal properties and nonlinear absorption characteristics of V2CTx MXene presented herein demonstrate the application of photothermal effect-based polarization rotation for all-optical signal modulation. In our analysis, first, the nonlinear absorption coefficient of a V2CTx thin film was measured using an open-aperture z-scan technique. The estimated nonlinear absorption coefficient was approximately −9.26 × 103 cm/GW at 1560 nm. Next, density functional theory calculations were conducted to determine the electronic band structure and optical absorption spectrum of V2CTx MXene. Following this, photothermal properties of V2CTx MXene were characterized in terms of the photothermal effect-based polarization rotation using 980 nm control and 1550 nm probe beams. The power-dependent temperature slope and conversion efficiency of the phase shift were measured to be 0.15 °C/mW and 0.02 π/mW, respectively. Finally, an all-optical modulator was experimentally implemented using the photothermal effect-based polarization rotation. The rise and fall time constants were estimated to be approximately 311 and 321 μs, respectively.

A new copper hybrid compound based on 3,3'-diaminodiphenylsulfone as ligand: Growth, crystal structure, spectroscopic analysis, and thermal behavior

A new copper compound with general formula [H2L]2(CuCl4(H2O)2).2Cl·2H2O [L = 3,3′-diaminodiphenylsulfone] was synthesized, at room temperature, by slow evaporation method. The morphology was observed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscope (EDS). The single crystal X-ray analysis indicates that the studied compound crystallizes in the P-1 triclinic space group. The packing pattern is characterized by organic and inorganic layers alternation stabilized by means of hydrogen interactions. Hirshfeld Surface analysis in combination with 2D fingerprint plots reveal the quantitatively relative contributions of these intermolecular interactions. Infrared and Raman spectroscopic analysis were performed to distinguish the different chemical functional groups and their environments in this compound. Additionally, the optical study was inspected by UV–visible and photoluminescence measurements. The compound exhibits three optical absorption bands at 245, 308 and 554 nm, with 1.54 and 1.64 eV indirect and direct gap energies values, respectively. Thermal analysis (TGA and DSC) was also investigated.

Face-Centered Cubic Silver Nanoclusters Consolidated with Tetradentate Formamidinate Ligands.

Growing attention has been paid to nanoclusters with face-centered cubic (fcc) metal kernels, due to its structural similarity to bulk metals. We demonstrate that the use of tetradentate formamidinate ligands facilitate the construction of two fcc silver nanoclusters: [Ag52(5-F-dpf)16Cl4](SbF6)2 (Ag52, 5-F-Hdpf = N,N'-di(5-fluoro-2-pyridinyl)formamidine) and [Ag53(5-Me-dpf)18](NO3)5 (Ag53, 5-Me-Hdpf = N,N'-di(5-methyl-2-pyridinyl)formamidine). Single-crystal X-ray structural analysis revealed that the silver atoms in both clusters are in a layer-by-layer arrangement, which can be viewed as a portion of the fcc packing of silver. The nitrogen donors of amidinate ligands selectively passivate the {111} facets. All silver atoms are involved in the fcc packing, that is, no staple motifs are observed due to the linear arrangement of the four N donors of the dpf ligands. The characteristic optical absorption bands of Ag52 and Ag53 have been studied with a time-dependent density functional theory. This work provides a facile access to assembling atomically precise fcc-type nanoclusters and shows the prospect of amidinates as protecting ligands in synthesizing metal nanoclusters.

Single-layer and bilayer MoSTe for photocatalytic water splitting: Role of optical absorption correction and band edge distribution

Single-layer and bilayer Janus transition metal dichalcogenides (TMDCs) attain great attention for possible application in solar water splitting. The crucial issues for solar water splitting are the band edge positions and optical absorption of photocatalysts. However, for this large group of Janus TMDCs materials, their optical absorption correction by the effective unit cell volume and the charge distribution of band edges, were not investigated in most previous works. To clarify these issues, we herein studied the electronic and optical properties of typical single-layer and bilayer MoSTe using first-principles calculations. Remarkably, when corrected by the effective unit cell volume, the optical absorption of bilayer MoSTe is not enhanced when compared to that of single-layer MoSTe. On the other hand, single-layer MoSTe possesses no solar water-splitting ability for lack of suitable band edges, when the charge distribution of band edges is considered. Furthermore, favorable band edges for water splitting were achieved in bilayer MoSTe. In brief, this work emphasized the optical absorption correction by the effective unit cell volume and the charge distribution of band edges when searching for 2D photocatalysts stacking by Janus monolayers.