Optical Absorption Characteristics Research Articles

Facile Synthesis of Monodispersed Titanium Nitride Quantum Dots for Harmonic Mode-Locking Generation in an Ultrafast Fiber Laser.

As a member of the transition metal nitride material family, titanium nitride (TiN) quantum dots (QDs) have attracted great attention in optical and electronic fields because of their excellent optoelectronic properties and favorable stability. Herein, TiN QDs were synthesized and served as a saturable absorber (SA) for an ultrafast fiber laser. Due to the strong nonlinear optical absorption characteristics with a modulation depth of ~33%, the typical fundamental mode-locked pulses and harmonics mode-locked pulses can be easily obtained in an ultrafast erbium-doped fiber laser with a TiN-QD SA. In addition, at the maximum pump power, harmonic mode-locked pulses with a repetition rate of ~1 GHz (164th order) and a pulse duration of ~1.45 ps are achieved. As far as we know, the repetition rate is the highest in the ultrafast fiber laser using TiN QDs as an SA. Thus, these experimental results indicate that TiN QDs can be considered a promising material, showing more potential in the category of ultrafast laser and nonlinear optics.

First-principles calculations of the structural, electronic and optical properties of Cs2AgxNa1-xInBr6 double perovskites

Inorganic halide double perovskite materials A2B+B3+X6 have attracted extensive attention due to the diversity of the composition and electronic structure, physicochemical stability, and potential photoelectric applications. Considering that Cs2AgInBr6 and Cs2NaInBr6 compounds are both of direct band gap, while the band gap values are quite different, here, using first-principles calculations, we studied the crystal structural, electrical and optical properties of the Cs2AgxNa1-xInBr6(x = 0, 0.25, 0.5, 0.75, 1) compounds with tunable band gap. We show that the crystal structures of the Cs2AgxNa1-xInBr6 compounds changes with the × values, and that, with the increasing of Ag ion, the band gap of Cs2AgxNa1-xInBr6 shows a nearly linear decreasing trend within 1.5–3.04 eV. In addition, the optical absorption characteristics show that the Cs2AgxNa1-xInBr6 compounds processes wide potential optoelectronic applications for their tunable electronic properties.

Photogenerated cathodic protection properties of Ag/Ag3PO4/TiO2 nanocomposites

Using immersion-deposition and photoreduction methods, high-purity Ag3PO4 and Ag nanoparticles were compounded on the surface of TiO2 nanowires. The cathodic protection effect of Ag/Ag3PO4/TiO2 nanocomposites on 304 stainless steel, as well as the morphology, composition, and optical absorption characteristics of the material were studied. When the number of impregnation-deposition cycles of Ag3PO4 was 6 and the concentration of AgNO3 in the photoreduction process was 0.1 M, the prepared Ag/Ag3PO4/TiO2 nanocomposites provided the best cathodic protection to 304 stainless steel. Relative to the saturated calomel electrode, the protection potential reached −900 mV, and the protection current reached 130 µA/cm2.

Spectroscopic properties of Nd3+ ions in Li2O[sbnd]MO (M=Mg, Ca and Sr)[sbnd]Sb2O3 glasses

The primary objective of the present work is to study the spectroscopic properties of Nd3+ ions in Li2OMO (M=Mg, Ca and Sr)Sb2O3 glass system. The current glass samples have been synthesized by the melt-quenching technique. The physical and thermal properties of the prepared glass samples have been calculated. Optical absorption, IR, photoluminescence (PL) and decay characteristics were recorded at ambient temperature. The Judd–Ofelt (J-O) intensity parameters Ω2, Ω4 and Ω6 for Nd2O3 mixed glasses were calculated using absorbance spectra and found to be the order Ω2 > Ω6 > Ω4. The SrO mixed glass sample J-O parameter Ω2 is found to be the lowest and has the highest emission intensity, radiative probability (A) and branching ratio (β) compared to other two glass samples MgO and CaO. The lifetime of 4F3/2 transition has been experimentally recorded at λexc= 585 nm and found that SrO mixed glass is a favorable one and getting the highest quantum efficiency (η = 64.5%). The chromaticity coordinates confirmed that the prepared glass samples were potential under 585 nm excitation wavelength. The IR studies suggest that the structural disorder may reduce the low phonon losses and increase the PL output in SrO mixed glasses. The studied results may useful for enhancing optical amplification as well as potential to generate in solid state NIR laser applications at 1.066 µm.

Carboranethiol-Protected Propeller-Shaped Photoresponsive Silver Nanomolecule

We report the synthesis, structural characterization, and photophysical properties of a propeller-shaped Ag21 nanomolecule with six rotary arms, protected with m-carborane-9-thiol (MCT) and triphenylphosphine (TPP) ligands. Structural analysis reveals that the nanomolecule has an Ag13 central icosahedral core with six directly connected silver atoms and two more silver atoms connected through three Ag-S-Ag bridging motifs. While 12 MCT ligands protect the core through metal-thiolate bonds in a 3-6-3-layered fashion, two TPP ligands solely protect the two bridging silver atoms. Interestingly, the rotational orientation of a silver sulfide staple motif is opposite to the orientation of carborane ligands, resembling the existence of a bidirectional rotational orientation in the nanomolecule. Careful analysis reveals that the orientation of carborane ligands on the cluster's surface resembles an assembly of double rotors. The zero circular dichroism signal indicates its achiral nature in solution. There are multiple absorption peaks in its UV-vis absorption spectrum, characteristic of a quantized electronic structure. The spectrum appears as a fingerprint for the cluster. High-resolution electrospray ionization mass spectrometry proves the structure and composition of the nanocluster in solution, and systematic fragmentation of the molecular ion starts with the loss of surface-bound ligands with increasing collision energy. Its multiple optical absorption features are in good agreement with the theoretically calculated spectrum. The cluster shows a narrow near-IR emission at 814 nm. The Ag21 nanomolecule is thermally stable at ambient conditions up to 100 °C. However, white-light illumination (lamp power = 120-160 W) shows photosensitivity, and this induces structural distortion, as confirmed by changes in the Raman and electronic absorption spectra. Femtosecond and nanosecond transient absorption studies reveal an exceptionally stable excited state having a lifetime of 3.26 ± 0.02 μs for the carriers, spread over a broad wavelength region of 520-650 nm. The formation of core-centered long-lived carriers in the excited state is responsible for the observed light-activated structural distortion.

Passively Q-Switched and Mode-Locked Fiber Laser Based on a Zeolitic Imidazolate Framework-67 Saturable Absorber

Exploring new saturable absorber (SA) materials with excellent performance to achieve Q-switching and mode-locking operations is a hot topic in ultrafast laser research. The impressive specific surface areas, structural tunability, and high thermal and chemical stability of the zeolitic imidazolate framework (ZIF) materials make them promising candidates as high-performance SAs. In this work, we demonstrated the potential of the ZIF-67 SAs for ultrafast fiber laser applications. The nonlinear optical absorption characteristics of the ZIF-67 SAs at the telecommunication band were investigated by using the balanced twin-detector method. By incorporating the ZIF-67 SAs into the Er3+-doped fiber laser cavity, stable Q-switching and mode-locking operations were achieved. The research results are essential for promoting the application of novel hybrid nanomaterials in ultrafast lasers.

Influence of weathering exposure on UV light absorption in low density polyethylene LDPE grad-LA071

The effect of weathering exposure on optical absorption characteristics of LDPE grad-LA071 has been investigated in different durations of time. Generally, it is revealed that optical absorption of LDPE grad-LA071 decreases exponentially with wavelength in different durations of time. In addition, the optical absorption increased significantly with during time of exposure to weathering, especially for high frequencies, recommending that LDPE grad-LA071 is practical candidate as a selective filter for UV light. Therefore, LDPE grad-LA071 can be used as UV light masks in semiconductor devices and used as protective shields for solar cells to lower UV light exposure. Furthermore, LDPE grad-LA071 film can be used in packaging to increase the lifespan of various items such as electronics, furniture, food, and medications. The absorption spectra have been analyzed, finding a non-monotonically variation in the optical energy gap with durations of time of weathering exposure.

Oxygen vacancies in KTiOPO4 : Optical absorption from hybrid DFT

Density functional theory is used to calculate the optical absorption of oxygen vacancies in potassium titanyl phosphate ($\mathrm{K}\mathrm{Ti}\mathrm{O}\mathrm{P}{\mathrm{O}}_{4}$, KTP) crystals. A modified hybrid functional is used for the description of the midgap defect states and the optical excitation energies. Oxygen vacancies in the $+2$ charge state lead to rather minor modification of the bulk KTP optical response, while the $+1$ and neutral charge states give rise to characteristic midgap optical absorption covering the whole near-infrared and visible spectrum. Its intensity is strongly polarization dependent and strongest for light polarized parallel to the $z$ axis. The modification of the KTP optical absorption by oxygen vacancies predicted here corroborates the picture that the gray-track formation in KTP, i.e., its photochromic damage, is related to a successive charging of oxygen vacancies.

Optical and luminescence properties of Er3+ doped Sb2O3–Li2O‒MO (M=Mg, Ca and Sr) glasses

Sb2O3–Li2O–Er2O3glasses mixed with various modifier oxides viz., MgO, CaO and SrO have been prepared by the melt quenching technique in this present work. Optical absorption, photoluminescence and decay characteristics were measured at room temperature. The Judd-Ofelt (JO) parameters Ω2, Ω4 and Ω6 for Er2O3 mixed glasses were calculated using absorbance spectra. The emission spectra excited λexc = 380 nm exhibited emission transitions 4F7/2, 2H11/2, 4S3/2, 4F9/2 → 4I15/2 (Vis region) and 4I13/2 → 4I15/2 (NIR region) of Er3+ doped glasses. Numerous characteristics of radiative parameters viz., AR, βR, τR, and σEP for Er2O3 enriched glasses were analyzed and reported, based on JO parameters and the emission spectra. Overall, the results indicated that Er3+ mixed glasses exhibited a substantial increase in the green emission (2H11/2, 4S3/2 → 4I15/2) intensity of all glass samples. When compared with the other two glasses, the SrO mixed glass having the highest quantum efficiency (η = 88.2%) of green emission. The structural modifications of Er3+ ions due to modifier oxides were identified by IR spectral studies.

Effect of Cr co-doping on the optical absorption and emission characteristics of Yb:YVO4 single crystals grown by OFZ technique

Cr co-doped Yb:YVO4 (Cr:Yb:YVO4) single crystals with concentrations of 1.0 and 1.5 at.% of Cr and 3.0 at.% of Yb were grown by the optical floating zone technique. X-ray diffraction analysis on the grown crystals revealed that the lattice parameters of Cr:Yb:YVO4 crystals do not depend on the Cr doping concentration. The dislocation etch pit density estimated from the etching study was found to be 103/cm2. The observed fringes of nearly uniform thickness and spacing in birefringence interferometry for [100] plate and conoscopy pattern for [001] plate indicate the compositional and optical homogeneity of the crystal. Further, the influence of the Cr doping concentration on the 2A1→2B2 transition (at ∼1100 nm) and 2A1→2E transition (at ∼640 nm) due to Cr5+ ion were analysed using two orthogonal polarized light with electric field perpendicular (π-polarization) and parallel (σ-polarization) to [001] axis. These absorption peaks of Cr ion were found to be sensitive to the polarization of incident light. The absorption transition 2A1→2B2 around 1100 nm are permitted for π-polarization and on the other hand, the absorption transition 2A1→2E at 640 nm are permitted only for σ-polarization. The characteristic broader absorption band around ∼1100 nm is of importance as it is useful for self-Q-switching in a laser gain medium. The absorption coefficient corresponding to Cr5+ ions at 1100 nm increases with the increase in Cr doping concentration. The band-gap for σ-polarized light is slightly higher than π-polarized light and decreases with Cr doping. The increase in the estimated Urbach energy (50–122 meV) with the increase in the Cr doping concentration confirms that the defect states close to the band edge increase thus decrease the band gap. Further the photoluminescence intensity is in-line with the absorption data and decreases with increase in the Cr concentration from 0 to 1.5 at.%.

Synthesis of NixMg1-xO nano particles solid solution by sol-gel self combustion method and investigation of its structural and optical properties

In this paper, the NixMg1-x O (0.1 ≤ x ≤ 0.4) solid solution nano-powder was synthesized by new and soft non-alkoxide sol-gel self-combustion method. In this method, Ni(NO3)3·6H2O, Mg(CH3COO)2·4H2O and Citric acid (CA), were used as Ni2+, Mg2+ ion and gelling and combusting source, respectively. Then, by thermal gravimetric analysis (TGA) the chemical reaction and the appropriate temperature to form a stable compound were determined. The influences of molar ratio of component (x) on structural and optical properties of samples have been investigated by X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and Fourier transform infrared (FTIR) analysis. By increasing in x, all the samples are shown decreasing ecreasing in lattice parameter (a) and crystallite size (D), which indicates the contamination of magnesium oxide with nickel and the formation of NixMg1-xO solid solution. The Band gap was decreased by increasing in x which shows that Ni2+ ions in MgO structure causes some modifications in the energy levels and the optical absorbance characteristics associated with F centers due to oxygen defect centers.

Microstructure Study and Linear/Nonlinear Optical Performance of Bi-Embedded PVP/PVA Films for Optoelectronic and Optical Cut-Off Applications.

Hybrid polymer films of polyvinyl pyrrolidone (PVP)/polyvinyl alcohol (PVA) embedded with gradient levels of Bi-powder were prepared using a conventional solution casting process. XRD, FTIR, and SEM techniques have been used to examine the micro/molecular structure and morphology of the synthesized flexible films. The intensities of the diffraction peaks and transmission spectrum of the PVP/PVA gradually declined with the introduction of Bi-metal. In addition, filler changes the microstructure surface of the pure film. The modification in the microstructure leads to an enhancement in the optical absorption characteristic of the blend films. The indirect allowed transition energy was calculated via Tauc’s and ASF (Absorption Spectra Fitting) models. The decrease in the hybrid film’s bandgap returns to the localized states in the forbidden region, which led the present films to be suitable for photo-electric, solar cell, etc., applications. The relation between the transition energy and the refractive index was studied. The enhancement in the refractive index with Bi-metal concentrations led to use the as-prepared films in optical sensors. The rise of Bi-metal concentrations leads also to the improvement of the nonlinear susceptibility and refractive parameters. The optical limiting characteristics revealed that the higher concentration dopant films reduce the light transmission intensity which is appropriate for laser attenuation and optical limiting in photonic devices. The results suggest that hybrid films are promising materials in a wide range of opto-electronic applications.

NbCX (X = F, Cl, Br, I) with Highly Anisotropic Optical, Mechanical and Electric Transport Properties

Two-dimensional materials with anisotropic properties (for example, mechanical, optical, and electrical transmission anisotropy) have been sought for a long time, especially two-dimensional materials with strong electrical transport anisotropy. Here, we report a class of two-dimensional NbCX(X=F,Cl,Br,I) monolayers with stable performance. Using density functional theory combined with the method of non-equilibrium Green's function, we found that the optical absorption characteristics of two-dimensional NbCX are highly dependent on the crystal lattice direction. The calculated electrical transport properties also show that the NbCX monolayer exhibits strong anisotropy in the bias voltage range of 0.1∼2.0 V. NbCX prefers to transmit current in the a direction, which can be orders of magnitude up to µA. The anisotropy, adjustable band gap and unique transport properties of two-dimensional NbCX can have potential applications in nano-optoelectronics.

Nonlinear optical absorption characteristics and ultrafast carrier dynamics of one-dimensional strongly correlated cuprate nanosheets

Developing novel optical materials with large and ultrafast nonlinear optical (NLO) response is significant for photonics and optoelectronics. Cuprates as the representative one-dimensional (1D) strongly correlated material show promising NLO properties, but relevant research is quite rare. Here, using Ca2CuO3 nanosheets as the prototype, we systematically explored the NLO performance and ultrafast carrier dynamics of these cuprate nanosheets prepared by a ball-milling process. The obtained Ca2CuO3 nanosheets exhibited convertible NLO behavior from saturable absorption (SA) to reverse saturable absorption (RSA) with strong absorption coefficient, induced by increasing wavelengths and duration of excitation pulse. In addition, we revealed their ultrashort relaxation time in (sub-)picosecond scale for photogenerated carriers, mainly owing to the midgap state-assisted recombination by emitting multiple phonons and spinons. Furthermore, the similar NLO feature also investigated in isostructural Sr2CuO3 and Ba2CuO3 nanosheets further indicated the excellent NLO performance of 1D strongly correlated cuprates. This work opens up a new avenue for future photonics with 1D strongly correlated materials as the novel platforms.

Review of Thermoplastic Drawing with Bulk Metallic Glasses

This study summarizes the recent progress in thermoplastic drawing of bulk metallic glasses. The integration of drawing with templated embossing enables the fabrication of arrays of high-aspect-ratio nanostructures whereas the earlier drawing methodologies are limited to a single fiber. The two-step drawing can produce metallic glass structures such as, vertically aligned nanowires on substrates, nanoscale tensile specimens, hollow microneedles, helical shafts, and micro-yarns, which are challenging to fabricate with other thermoplastic forming operations. These geometries will open new applications for bulk metallic glasses in the areas of sensors, optical absorption, transdermal drug-delivery, and high-throughput characterization of size-effects. In this article, we review the emergence of template-based thermoplastic drawing in bulk metallic glasses. The review focuses on the development of experimental set-up, the quantitative description of drawing process, and the versatility of drawing methodology.

Red-shifted optical absorption in films of azo-polyurea - polystyrene blends: Structural correlations and implications

We report the optical absorption characteristics in thin film coatings of a blend of two polymers: azo-polyurea (azo-PU) and polystyrene (PS). It is shown using UV–visible spectroscopy that the absorption spectrum of the resultant blend undergoes a distinct and decisive redshift towards the visible wavelength regime, accompanied by broadening and overlapping of the characteristic absorption peaks. Light exposure studies reveal that the red-shifted optical absorption induces trans to cis isomerization of the blended polymer films upon exposure to visible wavelengths, which would otherwise occur typically only by stimulus from ultraviolet wavelengths. The extent of redshift in the absorption maxima and broadening in the absorption spectrum of the polymer blend films are found to be sensitive to the amounts of the constituent polymers. The changes in spectral configuration are understood in terms of lattice structural changes that occur in azo-PU chains due to the incorporation of PS, in particular the disarrangement in hydrogen bonding. It is suggested that the modified optical absorption characteristics would endow significant advantages, such as the possibility of replacing UV with visible light in applications requiring cis → trans and trans → cis isomerization, as well as photoswitchability due to trans-cis-trans cycling.

Influence of iron (III) oxide on the optical, mechanical, physical, and radiation shielding properties of sodium-barium-vanadate glass system

The physical, optical, mechanical, and radiation absorption features of a Sodium-barium-vanadate glass system containing iron (III) oxide were obtained by direct calculations and Monte Carlo simulations in this study. The investigated glasses have a chemical definition given as (20 – x)Na2O + 25BaO + 55V2O5 + xFe2O3 (where x = 0, 5 10, 20 mol% represents SBV-Fe0–3). The mass density from 3.732 to 4.326 g cm−3 while molar volume decreased from 40.40 to 39.37 cm3 mol−1 as the Fe2O3 insertion ratio rose in the glasses. Replacing Na2O with Fe2O3 in the glasses led to a decrease in the refraction index, reflectance loss, and metalization criterion of the glasses, while on the other hand the optical transmittance increased. The Young's, longitudinal, bulk, and shear moduli all increased as the glass density improved. The gamma radiation shielding competence evaluated from FLUKA simulations and confirmed by XCOM calculations revealed that the incident photon energy and the chemical structure of the glasses influenced the photon absorbing capacity of the glasses. The linear attenuation coefficient decayed from 0.4852 to 0.1409 cm−1 for SBV-Fe0 while that of SBV-Fe1, SBV-Fe2, and SBV-Fe3 decayed from 0.5021 to 0.1479 cm−1, 0.5203 to 0.1544 cm−1, and 0.5573 to 0.1656 cm−1 accordingly as energy increases from 0.284 to 2.506 MeV. Similarly, the mass attenuation coefficient, effective atomic number and other estimated photon absorption quantities all point to an improved absorption capacity with the trend SBV-Fe0 < SBV-Fe1 < SBV-Fe2 < SBV-Fe3. Further, the ΣR of the glasses have values of 1.2162, 1.1977, 1.1919, and 1.213 cm−1 for the SBV-Fe0–3 respectively. Analysis of the thermal neutron cross section of the glasses reveals that the inclusion and subsequent increase of the Fe2O3 content of the SBV-Fe glasses has a positive impact on the thermal neutron interaction parameters. SBV-Fe glasses are valuable materials for radiation absorption functions when compared with common shields.

Optical and electromagnetic absorption features of hierarchical pampon and cauliflower-like magneto/dielectric composite based absorber for C and X bands application

Hydrothermal and in-situ polymerization methods were used to successfully fabricate a pompon flower-like CoGd0.5Fe1.5O4 (CG) as a magnetic component and a cauliflower-like poly(indole-co-Py) (PP) co-polymer as a dielectric component for microwave absorption. The physico-chemical properties of CG/PP samples were determined via XPS, XRD, FTIR, BET, UV–vis, EDS, and FESEM analysis. VNA and VSM were used to evaluate the dielectric and electromagnetic properties of the CG and PP samples. The results of the absorption capability tests revealed that bi-layer samples outperformed single layer samples in terms of microwave dissipation capability. The thickness and arrangement of each layer in bilayer absorber effectively adjusted via MATLAB simulation. As a consequence, the effective absorption bandwidth in the bilayer absorber has been increased and covers the C and X bands entirely with a thickness of only 2 mm, in which 1 mm of CG composite layer with 1 mm of thickness is placed as an absorbing layer and a PP composite layer with 1 mm of thickness is considered as a matching layer. The hierarchical structure of both components (pompon and cauliflower-like morphology) may increase interfacial polarization, relaxation loss, and consequently attenuation constant of the absorber as well as improve impedance matching characteristics and decrease in density. Synergistic effects between two distinct layers containing magnetic and dielectric components may further increase the absorption feature.

Modification of optical emission in electrospun PVA nanofibers: effect of cerium oxalate crystals doped with neodymium and praseodymium

ABSTRACT Development of functional nanofibers from transparent polymer systems attracted attention of researchers recently. Doping of functional nanoparticles in a suitable polymer matrix in the nanofiber forms enables them as active materials for photonic, electronic and for energy generation applications. Cerium oxalate crystals in its pure and rare earth-doped form are found to be a potential system for such investigations. Cerium oxalate crystals and its praseodymium (Pr3+)- and neodymium (Nd3+)-doped forms were synthesized by single diffusion gel growth method. These crystals, in the powder form, were incorporated in PVA matrix to form nanofibers (NFs) by electrospinning technique. Morphological studies were done by scanning electron microscopy (SEM). From the X-ray powder diffraction analysis, monoclinic structure of Ce2(C2O4)3 was confirmed. The notable changes observed in the FTIR spectra revealed interactions between the cerium ions and polymer PVA. The optical absorption characteristics of pure and doped PVA NFs were done by UV–Visible absorption spectroscopy. The photoluminescence spectrum of the rare earth-doped cerium oxalate-PVA NFs showed that the fiber had strong emission in the blue-green region.

Synthesis and Characterization of Enantiopure Chiral Bis NHC-Stabilized Edge-Shared Au10 Nanocluster with Unique Prolate Shape

Herein we report the first chiral Au10 nanoclusters stabilized by chiral bis N-heterocyclic carbene (bisNHC) ligands. ESI-MS and single-crystal X-ray crystallography confirmed the molecular formula to be [Au10(bisNHC)4Br2](O2CCF3)2. The chiral Au10 nanocluster adopts a linear edge-shared tetrahedral geometry with a prolate shape. DFT calculations provide insight into the electronic structure, optical absorption, and circular dichroism (CD) characteristics of this unique Au10 nanocluster. CD spectra demonstrate chirality transfer from the chiral bisNHC ligand to the inner Au10 nanocluster core. Examination of ESI-MS and UV-vis spectra show that cluster [Au9(bisNHC)4Br]Br2 is formed initially and then transformed into the Au10 nanocluster in solution.