Broadband Research Articles

Ultralow Voltage High-Performance Nanocellulose-Based Electro-Ionic Actuators for Soft Robots.

High-performance eco-friendly soft actuators showing large displacement, fast response, and long-term operational capability require further development for next-generation bioinspired soft robots. Herein, we report an electro-ionic soft actuator based on carboxylated cellulose nanocrystals (CCNC) and carboxylated cellulose nanofibers (CCNF), graphene nanoplatelets (GN), and ionic liquid (IL). The actuator exhibited exceptional actuation performances, achieving large displacements ranging from 1.6 to 12.3 mm under ultralow actuation voltages of 0.25-1.5 V. It also operated stably across a broad frequency band from 0.1 to 10 Hz and displayed a significant working stability of 99.3% after up to 240 cycles. Remarkably, the electro-active actuator demonstrated a fast response (0.39 s delay under 1.0 V at 0.1 Hz), and a long lifespan (with only a minor decrease of 2% for 2 years). The enhanced actuation performances of the actuator were attributed to its superior ionic conductivity, high charge storage ability, strong ionic interaction, and physical-chemical cross-linked networks. Furthermore, we successfully demonstrated the bioinspired applications of CCNC/CCNF-IL-GN actuators including micro-grippers, spiral-structure electroactive stents, biomimetic fingers, and bionic dragonfly wings. The proposed actuator and its bioinspired robot designs could offer a significant way for the development of next-generation eco-friendly soft actuators, soft robots, and biomedical microdevices in microenvironments requiring low-voltage environment.

Synthesis, characterization, and investigation of photoluminescence optima of In3+ and Gd3+ doped Eu1.90In0.10Ru2O7 and Eu1.90Gd0.10Ru2O7 materials

In this study, we investigated the photoluminescence properties and structure of the In3+ and Gd3+ doped Eu2Ru2O7-based pyrochlore materials. The samples were synthesized by solid state reaction technique, investigated structurally by X-ray powder diffraction (XRD), thermally by thermogravimetry, and differential thermal analysis, morphologically by scanning electron microscopy (SEM). The photoluminescence properties of Eu1.90In0.10Ru2O7 and Eu1.90Gd0.10Ru2O7 were investigated with photoluminescence spectrometer. X-ray diffraction patterns of all the samples showed that all samples had a cubic type pyrochlore crystal structure with a = b = c = 10.252 Å and α = β = γ = 90°. The XRD patterns demonstrate that neither the type nor the amount of doping ion alters the unit cell parameter. The SEM images of Eu1.90In0.10Ru2O7 and Eu1.90Gd0.10Ru2O7 reveal a regular morphology, with an average sample size ranging from 0.2 to 0.5 μm. The elementel (EDX) analysis confirm the absence of impurity elements and showing that the theoretical and experimental element ratios are consistent with EDX analysis expectations. The pyrochlore phosphors showed broad red emission band at ∼605 nm. This red emission can be attributed to the 5D0→7F2 transitions of Eu3+. The phosphor co-doped with In3+ ions has a considerably longer lifetime and photoluminescence intensity than the other phosphor. Eu1.90In0.10Ru2O7 and Eu1.90Gd0.10Ru2O7 phosphors, which show transitions in the red region (at 605/606 nm,5D0 →7F2), are suitable for optoelectronic and white LED applications.

Catalyst-assisted growth of CsPbBr3 perovskite nanowires.

Halide perovskites (HPs), particularly at the nanoscale, attract attention due to their unique optical properties compared to other semiconductors. They exhibit bright emission, defect tolerance, and a broad tunable band gap. The ability to directly transport charge carriers along the HPs nanowires (NWs) has led to the development of methods for their synthesis. Most of these methods involve some version of an oriented attachment step with various modifications. In this study, we introduce CsPbBr3 nanowires produced via the solution-solid-solid (SSS) catalyst-assisted growth mechanism for the first time. We explored the kinetics of this process and examined the connection between the catalyst phase and its reactivity. We show how HP NWs grow with different SSS catalysts (i.e., Ag2S, Ag2Se, CuS) and discuss the required conditions for successful synthesis utilizing this mechanism. This method opens up a new avenue for producing HP NWs, which can be used to design and form new types of hybrid nanostructures.

Observation of Cartesian light propagation through a three-dimensional cavity superlattice in a silicon photonic band gap crystal

We experimentally investigate peculiar light propagation inside a three-dimensional (3D) superlattice of resonant cavities that are confined within a 3D photonic band gap. To this end, we fabricated 3D diamondlike photonic crystals from silicon with a broad 3D band gap in the near-infrared and doped them with a periodic array of point defects. In position-resolved reflectivity and scattering microscopy, we observe narrow spectral features that match well with superlattice bands in band structures computed with the plane-wave expansion. The cavities are coupled in all three dimensions when they are closely spaced (aSL≤3a), and uncoupled when they are further apart. The superlattice bands correspond to light that hops in high-symmetry directions in 3D (“Cartesian light”) that opens applications in 3D photonic networks, 3D Anderson localization of light, and future 3D quantum photonic networks. Published by the American Physical Society 2024

Observing high dependence of red luminescence on localized symmetry in Mn4+ activated inverse spinel phosphors.

Localized symmetry has been shown to significantly impact the luminescence behavior of Mn4+ ions through the electron-phonon coupling process. Building on this characteristic, three types of inverse spinel structure oxides (Mg2XO4, where X = Ti, Ti/Ge, Ge) doped with Mn4+ were developed, exhibiting strong red emission when exposed to UV and blue light. A thorough examination reveals that the symmetric improvement of the Mn4+ sites within the octahedral environment leads to significant changes in their luminescence behavior, including a suppression of zero-phonon-line (ZPL) emission, a blueshift, and an extension of the luminescence lifetime. Moreover, variable-temperature PL spectra of phosphors are carefully measured. Low-temperature PL spectra demonstrate three distinct sharp emission peaks for Mg2GeO4:Mn4+, while Mg2TiO4:Mn4+ exhibits a broad emission band. The average primary phonon energies involved in the vibronic processes are determined through theoretical fitting of temperature-dependent PL intensities. Lastly, the luminescence dynamics associated with anti-Stokes, ZPL, and Stokes emissions are analyzed. The observed increase in luminescence lifetime indicates a significant impact of the localized environment on luminescence properties.

Two types of stimulated emission in HPHT diamond with a high concentration of NV centers

The paper presents the results of experimental observation of two types of stimulated emission (SE) under pulsed laser pumping at 532 nm in diamond with NV centers. A comprehensive spectroscopic characterization of multisectorial HPHT diamond plate was performed. At low pumping power, the stimulated emission from NV¯ centers was recorded as a broad (≥80 nm wide) band with a maximum at 706 nm in the {111} and {311} sectors of the diamond plate. As the pump power increased in the {111} sector, narrow-band stimulated emission (<10 nm wide) was detected, with a maximum at 716 nm and a luminescence impulse duration of 1.5–3 ns. As the pump density increased, a fine structure in the spectrum of narrow-band stimulated emission was revealed for the first time. The concentration of NV¯ centers in the {111} and {311} growth sectors was ≈10 ppm. However, there were considerable differences in the concentrations of C (35 and 3.5 ppm) and C+ centers (6.1 and 3.2 ppm, respectively). It was demonstrated that the presence of a high concentration of NV¯ centers is not the only necessary condition for the initiation of narrow-band SE in the 710–720 nm range. In the {311} sector, lighting at 360, 405, and 488 nm reduced the concentration of NV¯ centers by 15 % while increasing the concentration of C+ centers in the {311} sector. This effect is weak in the {111} sector. The authors suggested a model for narrow-band SE at the transition Valence Band → C+ with charge-state conversion of C↔C+ and NV0↔NV¯ centers. Further research on the dynamic processes is required in order to a detailed understanding of the operation of NV centers in diamond during SE generation.

Assessing the retrieval procedure of complex-valued forces from airborne pressure fields by means of DIC-based full-field receptances in simplified pseudo-inverse vibro-acoustics

Lightweight structural components in many engineering fields can be severely excited by airborne pressure fields, becoming a concern for their structural dynamics and reliability. Nowadays, the quality reached by optical measurements, in contactlessly estimating - as maps of displacements over force - complex-valued full-field receptances, allows an accurate description of the structural dynamics in a broad frequency domain, without any numerical structural model. This is even more relevant for lightweight components, otherwise affected by potential distortions, coming from the inertia of more traditional transducers. High-speed DIC structural testing is here combined with acoustic propagation in direct and pseudo-invertable vibro-acoustic FRFs, obtained by the simple Rayleigh integral approximation, here re-formulated to take advantage of the experiment-based full-field receptances, when a force excites a vibrating surface, which radiates sound pressure into air and vice-versa. Starting from airborne pressure fields, known in their spectra, the pseudo-inverse vibro-acoustics aims at identifying the force, with a broad frequency band, which can be transmitted to the excitation locations, previously used in defining the vibro-acoustic FRFs in the direct problem. Extended details and considerations on this full-field receptance-based vibro-acoustic approximation are thoroughly provided, with special attention to its complex-valued nature, to numerical precision and to broad dynamics' excitation signature, thanks to the accurate DIC-based testing of a real thin plate.

Portable real-time polarimeter for partially and fully polarized light.

We present a portable polarimeter capable of real-time visualization of partial and fully polarized light over a broad band of wavelengths. Our system utilizes a Raspberry Pi computer with a low-cost data acquisition "HAT" and an integrated photodetection circuit. Wide bandwidth operation is achieved through digital calibration of an arbitrary retardance waveplate presented herein. All mechanical, electrical, and software components are open source and available on a GitHub repository. This completely integrated approach provides an efficient tool for modern optics research laboratories and is well-suited for educational demonstrations.

Structure, microstructure, and ESR properties of concentration-dependent Zn1-xMnxO nanoparticles

In this study, the estimated stress, strain, and crystallite sizes of different Mn-doped ZnO nanoparticles were calculated using the Williamson-Hall method and compared with the values obtained from the Debye-Scherrer formula. Moreover, defects, and magnetic properties of Mn-doped ZnO nanoparticles at different concentrations were investigated. The sol-gel method was used to synthesize nanoparticles. The X-ray diffraction and Rietveld analysis results confirm that the desired structure is formed and that no secondary phase is present up to an Mn concentration of x=0.2. In and out of plane lattice parameters, cell volumes, bond length, atomic locality, and dislocation density (δ) were clarified. The grain size of the concentration-dependent samples was provided by scanning electron microscope. Photoluminescence (PL) spectra exhibited ultraviolet emission along with a broad band encompassing violet, blue, and red regions, attributed to defect-related and excitonic emissions. These emissions were notably influenced by synthesis conditions and doping elements and ratios. Electron spin resonance properties of the concentration-dependent samples were analyzed to figure out the g-factor through line widths of pike-to-pike (ΔHPP) of ESR spectra. Mn-doped ZnO nanoparticles exhibited ferromagnetism at room temperature.

Synthesis, Characterization and Photoluminescence Studies of near-UV excitable green-emitting NaBaScSi2O7: Eu2+ phosphor with high Internal Quantum Efficiency and Remarkable Thermal Stability

Green-emitting phosphor NaBaScSi2O7:Eu2+ was synthesized by “Amorphous Metal Complex” method using water soluble silicon compound. Eu2+ doped NaBaScSi2O7 exhibited a broad green emission band centered between 500 and 510 nm. The high luminescence intensity of the as-synthesized phosphors may owe to the synthesis procedure based on Amorphous Metal Complex (AMC) method which helps in the homogeneous distribution of Eu2+ ions in the matrix as well as the double annealing in graphite and H2/N2 reducing atmosphere. Upon excitation at 365 nm, the composition-optimized NaBaScSi2O7:Eu2+ exhibited strong green light peaking at 501 nm with the CIE chromaticity (0.146, 0.375) and a high internal quantum efficiency of about 77%. The thermally stable luminescence properties were also studied. The results indicate NaBaScSi2O7:Eu2+ as an attractive candidate for use as a conversion phosphor for Phosphor Converted White light-emitting diode (pc-WLEDs) applications.

An Activity-Based Sensing Approach to Multiplex Mapping of Labile Copper Pools by Stimulated Raman Scattering.

Molecular imaging with analyte-responsive probes offers a powerful chemical approach to studying biological processes. Many reagents for bioimaging employ a fluorescence readout, but the relatively broad emission bands of this modality and the need to alter the chemical structure of the fluorophore for different signal colors can potentially limit multiplex imaging. Here, we report a generalizable approach to multiplex analyte imaging by leveraging the comparably narrow spectral signatures of stimulated Raman scattering (SRS) in activity-based sensing (ABS) mode. We illustrate this concept with two copper Raman probes (CRPs), CRP2181 and CRP2153.2, that react selectively with loosely bound Cu(I/II) and Cu(II) ions, respectively, termed the labile copper pool, through copper-directed acyl imidazole (CDAI) chemistry. These reagents label proximal proteins in a copper-dependent manner using a dye scaffold bearing a 13C≡N or 13C≡15N isotopic SRS tag with nearly identical physiochemical properties in terms of shape and size. SRS imaging with the CRP reagents enables duplex monitoring of changes in intracellular labile Cu(I) and Cu(II) pools upon exogenous copper supplementation or copper depletion or genetic perturbations to copper transport proteins. Moreover, CRP imaging reveals reciprocal increases in labile Cu(II) pools upon decreases in activity of the antioxidant response nuclear factor-erythroid 2-related factor 2 (NRF2) in cellular models of lung adenocarcinoma. By showcasing the use of narrow-bandwidth ABS probes for multiplex imaging of copper pools in different oxidation states and identifying alterations in labile metal nutrient pools in cancer, this work establishes a foundation for broader SRS applications in analyte-responsive imaging in biological systems.

Advanced design and analysis of dual element MIMO antenna for Ultra-Wideband Applications

This investigation uses the Genetic Optimization Method to convert a wide-band MIMO antenna into a UWB (3.1GHz–10.6 GHz) MIMO antenna. Initially, a 22 × 42, mm2 wideband 2X2 MIMO antenna was designed using commercial Flame Retardant-4 material. The structure of the antenna patch was designed using half-circular forms on the half-ground plane. The designed MIMO antenna operates throughout a large frequency range of 4.8–9.8 GHz. While it was successful in achieving broad band characteristics, this MIMO antenna was unable to reach ultra-wide band characteristics. The MIMO antenna was operated in UWB ranges by a parametric study, which indicated that the resonating characteristics can be significantly modified by inserting a rectangular slot into the ground plane. Throughout the operational range, it was important to be concerned about improved gain and good isolation. Accordingly, optimization was carried out in order to accomplish the essential, multi-objective goals. The difficult multi-objective design goal is now reduced to an optimization challenge by means of genetic algorithm based random search. One of the performance goals that this optimization strategy aimed to fulfil was an increase in isolation to –20 dB across the entire Ultra-Wideband, with S11 being below –10 dB from 3.1 to 10.6 GHz. It is recommended to randomly select the parameters from their respective ranges for this work. This led to the selection of an optimizer based on random searches. In the operating range, the UWB has a respectable gain of 4 dB to 6 dB and increased isolation to –20 dB, according to the genetic algorithm optimizer’s execution of the predefined multiple-objective task.

Anionic polymers formed by dinuclear rhodium units and dicyanide silver/gold moieties

The synthesis, characterization and structural determination of four complexes with formula (PPh4)n{[Rh2(μ-O2CPh)4][Au(CN)2]}n (1) and Kn{[Rh2(μ-O2CR)4][M(CN)2]}n (M = Au, R CH2OEt (2), CH2OMe (3); M = Ag, R CH2OMe (4)) are described. In all cases, the [CN-M-CN]– (M = Au, Ag) group is bridging the axial positions of the dirhodium units giving one-dimensional chains. The packing of the chains in the solid state depends on the nature of the carboxylate group of the dimetallic unit, the counterion present in the complex and the metal itself. The most striking change is observed in the Kn{[Rh2(μ-O2CCH2OMe)4][Au(CN)2]}n complex (3), where the chains are positioned perpendicular to each other with an Au⋯Au interchain distance of 2.963 Å. The emission studies of this complex upon excitation at 350 nm show a clear broad emission band centered at 430 nm, while no luminescence is observed for the other compounds. The appearance of emission properties only in the case of complex 3 can be explained by its short aurophilic interactions.

Examining the contribution of Cu and Sr codoping on luminescence properties of borate crystals

Four crystals of Ba12(BO3)6[BO3][LiF4] (LBBF) with different ratios of co-dopants, Cu and Sr, were grown from high-temperature solutions. The LBBF structure is built from a porous [Ba12(BO3)6]6+ framework with channels along the optical axis filled with anionic groups. It was found that LBBF:Cu,Sr accommodates copper ions in the channels of the structure in both mono- and divalent states with the concentration of Cu + exceeding that of Cu2+, and Sr2+ replaces Ba2+ in the framework. At a constant concentration of copper and an increase in the concentration of strontium in the initial solution, the concentration of Cu+ in LBBF does not change monotonically but has a maximum. The broad photoluminescence band at about 410–440 nm is associated with the emission of Cu+ ions, while the bands at about 310–317 nm and 600 nm are related to Cu2+. All emissions demonstrate considerable temperature quenching in the range from 77 to 300 K. The LBBF:Cu crystals exhibit intense thermoluminescence (TL) in the range from 100 to 250 K after low-temperature X-ray irradiation, and peaks at about 315 and 380 K after room-temperature irradiation. With combined doping with strontium, the TL peaks shift to the region of higher temperatures, 365 and 410 K, without weakening the high-temperature component, which intensity linearly depends on radiation dose.

Influence of side-methyl substitution position on the phase state and microwave dielectric properties of triphenylacetylene-based liquid crystals.

Liquid crystal materials are well known in display applications, and their unique birefringence and electrical tunability can be utilised in microwave devices. This innovative technology modulates and filters microwave signals, replacing conventional semiconductors for a broad operational frequency band and tunable phase shift. Although isothiocyanatobiphenylacetylene-based liquid crystals exhibit low viscosity and large dielectric anisotropy, their applications in microwave communication are hampered by their broad near-crystalline phase temperature ranges. To address this limitation, this study designed and synthesized six fluorinated biphenylacetylene liquid crystal compounds with various benzene ring side-methyl substitutions (n = 3-5). The molecular structures, liquid crystal phases, and microwave dielectric properties were evaluated. Our findings indicate that compounds with methyl substitution at the Y2 position exhibited reduced melting points, an expanded nematic phase temperature range (ΔT n ≈ 92.3 °C), and an absence of near-crystalline phases. These compounds still maintain high microwave dielectric constants within the 9-30 GHz frequency band (Δε r = 0.9-1.3) and reduced maximum permittivity losses compared to their non-methyl-substituted counterparts, thereby improving the efficiency in the microwave frequency band. In contrast, the Y1 position substitution results in a significantly narrower nematic phase temperature range (approximately 2.6 °C on average) and a substantial decrease in the dielectric constant, with a Δε r reduction of about 0.3 compared to the Y2 substitution. This work shows that the side-methyl substitution can improve the performance of triphenylacetylene-based liquid crystals in microwave communication, providing valuable insight to aid the discovery of novel microwave liquid crystals.

9,10-Bis(5H-dibenzo[b,f]azepino)anthracene

The title compound with a donor–π–donor (D–π–D) type triad structure was synthesized by Buchwald–Hartwig amination using 9,10-dibromoanthracene and 5H-dibenzo[b,f]azepine, and characterized by 1H, 13C{1H} NMR, HRMS, and X-ray diffraction analysis. The azepine–anthracene–azepine units are nearly orthogonal to each other, with a torsion angle of 88°. A broad and weak absorption band around 410–480 nm and the low emission character (ΦF = 0.01) suggest the weak intramolecular charge transfer from the azepine to the anthracene unit due to the twisted structure.

Excitation-Power-Dependent Color Tuning in a Single Sn-Doped CdS Nanowire.

Multicolor emission and dynamic color tuning with large spectral range are challenging to realize but critically important in many areas of technology and daily life, such as general lighting, display, multicolor detection and multi-band communication. Herein, we report an excitation-power-dependent color-tuning emission from an individual Sn-doped CdS nanowire with a large spectral range and continuous color tuning. Its photoluminescence (PL) spectrum shows a broad trap-state emission band out of Sn dopants, which is superposed by whispering-gallery (WG) microcavity due to the nanostructure size and its structure, besides the CdS band-edge emission. By simply changing the excitation power from 0.25 to 1.36 mW, we demonstrate that the typical Sn-doped CdS nanowire with the weight ratio of 10:1 of CdS and SnO2, the emission color can change from red to orange to yellow to green. In view of the stable properties and large spectral range, the Sn-doped CdS nanowires are very promising potential candidates in nanoscale optoelectronic devices.

Potassium and Boron Co-Doping of g-C3N4 Tuned CO2 Reduction Mechanism for Enhanced Photocatalytic Performance: A First-Principles Investigation.

Graphitic phase carbon nitride (g-C3N4, abbreviated as CN) can be used as a photocatalyst to reduce the concentration of atmospheric carbon dioxide. However, there is still potential for improvement in the small band gap and carrier migration properties of intrinsic materials. K-B co-doped CN (KBCN) was investigated as a promising photocatalyst for carbon dioxide reduction via the Density Functional Theory (DFT) method. The electronic and optical properties of CN and KBCN indicate that doping K and B can improve the catalytic performance of CN by promoting charge migration and separation. In terms of the Gibbs free energy change, the CO2 reduction reaction catalysed by KBCN results in CH3OH, and its optimal pathway is CO2 → *CO2 → *COOH → CO → *OCH → HCHO → *OCH3 → CH3OH. Compared with CN, the doping elements K and B shift the rate-determining step from CO2 → *CO2 to *CO2 → *COOH. The K and B elements co-doping tuned the charge distribution between the catalyst and the adsorbate and reduced the Gibbs free energy of the rate-determining step from 1.571 to 0.861 eV, suggesting that the CO2 reduction activity of KBCN is superior to that of CN. Our work provides useful insights for the design of metallic-nonmetallic co-doped CN for photocatalytic CO2 reduction (CO2PR) reactions.

Study of the Photovoltaic Parameters of Inorganic Solar Cells Based on Cu&lt;i&gt;2&lt;/i&gt;O and CuO

A theoretical study of the photovoltaic parameters of inorganic solar cells based on ZnO/Cu2O and ZnO/CuO heterojunctions was carried out to improve the energy conversion efficiency. The influence of the thickness, charge carrier concentration and band gap of Cu2O and CuO films, as well as ZnO, on the photovoltaic parameters of solar cells has been studied. The simulation results showed that the efficiency of solar cells is significantly affected by the contact potential difference, the diffusion length of minority charge carriers, the amount of generated photocurrent and the recombination rate. The maximum efficiency of a solar cell based on ZnO/Cu2O was obtained equal to 10,63%, which is achieved with a band gap, thickness and charge carrier concentration in Cu2O equal to 1.9 eV, 5 μm and 1015 cm–3 and band gap, thickness and the concentration of charge carriers in ZnO is equal to 3,4 eV, 20 nm and 1019 cm–3, as well as the displacement of the edges of the conduction bands is 0.8 eV. For a solar cell based on ZnO/CuO, a maximum efficiency of 18.27% was obtained with a band gap, thickness and charge carrier concentration in CuO equal to 1.4 eV, 3 μm and 1017 cm–3, as well as a displacement of the conduction band edges of 0.03 eV. The obtained results of modeling solar cells can be used in the design and manufacture of inexpensive and efficient photovoltaic structures.

Energy Band Alignment and Defect Synergistic Regulation Enable Air-Solution-Processed Kesterite Solar Cells With the Lowest VOC Deficit.

The major challenge in preparing high-performance Cu2ZnSn(S,Se)4 solar cells is the large open circuit voltage deficit (VOC-def). A new strategy utilizing the synergistic substitution of Ag and In dual cations has been proposed to simultaneously address the problems of undesirable interface band alignment and high-density detrimental bulk defects, obtaining decreased carrier recombination rate and increased minority carrier lifetime. The shorter In-S/Se bonds move the CBM higher by generating stronger repulsive force than the Sn-S/Se bonds, thus adjusting the interface band alignment. Ag substitution can effectively suppress Cu─Zn disorder, while Ag, In dual substitution can further passivate Sn-related defects and solve the issue of low carrier concentration in Ag single-substituted samples. Besides, the superior carrier property of In-Se materials significantly enhanced the device carrier lifetime and minority carrier diffusion length. The state-of-the-art air-solution-processed CZTSSe device without any addition treatment with 14.33% efficiency and 580mV VOC is obtained, possessing the lowest VOC-def value currently available in the CZTSSe field (VOC/VOC SQ = 64.7%). This work emphasizes the synergistic modulation of band alignment, defect level, grain growth, and carrier transportation by dual cation substitution, which paves a convenient and effective way to realize high-performance solar cells and photovoltaic devices.