Spectral Range Research Articles

Realization of a Chiral Topological Whispering‐Gallery‐Mode Cavity in Gyromagnetic Photonic Crystals

AbstractPhotonic whispering‐gallery‐mode (WGM) cavities formed by total internal reflection of light around closed paths have played a central role in modern optics. Recently, extensive efforts have been devoted to achieving topologically photonic WGM cavities that are robust against defects or obstacles. However, previous experimental studies on topological photonic WGM cavities are limited to systems with time‐reversal symmetry (TRS) and weak topological protection due to the existence of backscattering channels. Here, the study reports the experimental realization of a chiral topological WGM cavity in a gyromagnetic photonic crystal with broken TRS. Using microwave near‐field measurements, it is directly observed that the chiral topological WGM cavities are inherently nonreciprocal and exhibit superior robustness against various obstacles with strong topological protection owing to the absence of backscattering channels. More interestingly, it is demonstrated that the resonance frequencies and free spectral range (FSR) of the chiral topological WGM cavities can be tailored by adjusting the insertion length of a metallic scatterer. The work extends the research realm of topological photonic WGM cavities and may find important applications in designing arbitrary‐shaped and nonreciprocal topological photonic cavities, filters, lasers, and frequency combs.

Fabrication of Black Silicon Antireflection Coatings to Enhance Light Harvesting in Photovoltaics

Black silicon has attracted significant interest for various engineering applications, including solar cells, due to its ability to create highly absorbent surfaces or interfaces for light. It enhances light absorption in crystalline solar cells, improving the efficiency of converting incident light into electricity for photovoltaic applications. This research focused on fabricating nanostructures that played a critical role in enhancing light absorption in the upper layers of solar cells. These nanostructures were created using the black silicon method, forming a layer known as “black silicon”. The coating not only improved the efficiency of crystalline solar cells but also enhanced their stability. The antireflection coating, composed of nanostructures with various shapes, including conical, pillar-like, and spike-like forms, achieved a reflectivity as low as 10% in the spectral range of 400–700 nm. This corresponded to a sample with α = 0.85 and a chuck bias of 4 W. An Inductively Coupled Plasma Reactive Ion Etching (ICP RIE) machine was employed to develop and control the specific shape, size, and density of the fabricated black silicon, which was then subjected to testing. The efficiency of the black silicon photovoltaic cell was 23.3%.

Resource-Efficient FPGA Architecture for Real-Time RFI Mitigation in Interferometric Radiometers

Interferometric radiometers operating at L-band, such as ESA’s SMOS mission, enable crucial Earth observations providing high-resolution measurements of soil moisture, ocean salinity, and other geophysical parameters. However, the increasing electromagnetic spectrum utilization has led to significant Radio Frequency Interference (RFI) challenges, particularly critical given the sensors’ fine temperature resolution requirements of less than 1 K. This work presents the hardware implementation of an advanced RFI detection and mitigation algorithm specifically designed for interferometric radiometers, targeting future L-band missions. The implementation processes 1-bit quantized signals at 57.69375 MHz from multiple receivers, employing time-frequency analysis and polarimetric detection techniques while optimizing Field Programmable Gate Array (FPGA) resource utilization. Novel optimization strategies include overclocked processing cores operating at 230.775 MHz, efficient resource sharing through operation serialization, and strategic memory management. The system achieves real-time processing capabilities while maintaining detection probabilities above 63% with false alarm rates below 1% for typical interference scenarios. Performance validation using synthetic datasets demonstrates robust operation across various RFI conditions, making this implementation suitable as part of the RFI detection and mitigation efforts for future interferometric radiometer missions beyond SMOS.

Unveiling the broadband optical properties of Bi2Te3: Ultrahigh refractive index and promising applications

van der Waals topological insulators, characterized by their high-index dielectric response, offer a promising materials platform for nanophotonics. Among these materials, Bi2Te3 has one of the highest refractive indices and extinction coefficients. However, the precise determination of Bi2Te3 optical properties remains challenging owing to its complicated physical model, which includes an oxide layer, topological conducting states, and optical anisotropy. Here, we resolve this problem and develop an accurate optical model for Bi2Te3 in a broad (450–1500 nm) spectral range. Our study shows that an oxide layer plays a major role in optical model for these wavelengths, while the influence of topological conducting states and optical anisotropy is minimal. Our model allows us to obtain accurate Bi2Te3 optical constants and demonstrate their use in biosensors, thermal theranostics, and topological phase singularities. Moreover, we observe a polarization transition of topological phase singularity for Bi2Se3, which opens a new direction for the development of topological phase effects. Therefore, our results open new avenues for photonic applications of Bi2Te3 optical properties.

Discrimination of leaf diseases in Maize/Soybean intercropping system based on hyperspectral imaging

In order to achieve precise discrimination of leaf diseases in the Maize/Soybean intercropping system, i.e. leaf spot disease, rust disease, mixed leaf diseases, this study utilized hyperspectral imaging and deep learning algorithms for the classification of diseased leaves of maize and soybean. In the experiments, hyperspectral imaging equipment was used to collect hyperspectral images of leaves, and the regions of interest were extracted within the spectral range of 400 to 1000 nm. These regions included one or more infected areas on the leaves to obtain hyperspectral data. This approach aimed to enhance the accurate discrimination of different types of diseases, providing more effective technical support for the detection and control of crop diseases. The preprocessing of hyperspectral data involved four methods: Savitzky-Golay (SG), Standard Normal Variate (SNV), Multiplicative Scatter Correction (MSC) and 1st Derivative (1st Der). The 1st Der was found to be the optimal preprocessing method for hyperspectral data of maize and soybean diseases. Competitive Adaptive Reweighted Sampling (CARS), Successive Projections Algorithm (SPA) and Principal Component Analysis (PCA) were employed for feature extraction on the optimal preprocessed data. The Support Vector Machines (SVM), Bidirectional Long Short-Term Memory Network (BiLSTM) and Dung Beetle Optimization-Bidirectional Long Short-Term Memory Network (DBO-BiLSTM) were established for the discrimination of maize and soybean diseases. Comparative analysis indicated that, in the classification of maize and soybean diseases, the DBO-BiLSTM model based on the CARS extraction method (1st Der-CARS-DBO-BiLSTM) demonstrated the highest classification rate, reaching 98.7% on the test set. The research findings suggest that integrating hyperspectral imaging with both traditional and deep learning methods is a viable and effective approach for classifying diseases in the intercropping model of maize and soybean. These results offer a novel method and a theoretical foundation for the non-invasive, precise, and efficient identification of diseases in the intercropping model of maize and soybean, carrying positive implications for agricultural production.

Tunable FSRS measurements with reduced background signals: Using an etalon filter to generate picosecond pump pulses in the 460-650nm range.

Generating wavelength-tunable picosecond laser pulses from an ultrafast laser source is essential for femtosecond stimulated Raman scattering (FSRS) measurements. Etalon filters produce narrowband (picosecond) pulses with an asymmetric temporal profile that is ideal for stimulated resonance Raman excitation. However, direct spectral filtering of femtosecond laser pulses is typically limited to the laser's fundamental and harmonic frequencies due to very low transmission of broad bandwidth pulses through an etalon. Here, we show that a single etalon filter (15cm-1 bandwidth; 172cm-1 free spectral range) provides an efficient and tunable option for generating Raman pump pulses over a wide range of wavelengths when used in combination with an optical parametric amplifier and a second harmonic generation (SHG) crystal that has an appropriate phase-matching bandwidth for partial spectral compression before the etalon. Tuning the SHG wavelength to match individual transmission lines of the etalon filter gives asymmetric picosecond pump pulses over a range of 460-650nm. Importantly, the SHG crystal length determines the temporal rise time of the filtered pulse, which is an important property for reducing background and increasing Raman signals compared with symmetric pulses having the same total energy. We examine the wavelength-dependent trade-off between spectral narrowing via SHG and the asymmetric pulse shape after transmission through the etalon. This approach provides a relatively simple and efficient method to generate tunable pump pulses with the optimum temporal profile for resonance-enhanced FSRS measurements across the visible region of the spectrum.

Plasmon-Enhanced Optoelectronic Graded Neurons for Dual-Waveband Image Fusion and Motion Perception.

Motion recognition based on vision detectors requires the synchronous encoding and processing of temporal and spatial information in wide wavebands. Here, the dual-waveband sensitive optoelectronic synapses performing as graded neurons are reported for high-accuracy motion recognition and perception. Wedge-shaped nanostructures are designed and fabricated on molybdenum disulfide (MoS2) monolayers, leading to plasmon-enhanced wideband absorption across the visible to near-infrared spectral range. Due to the charge trapping and release at shallow trapping centers within the device channel, the optoelectronic graded neurons demonstrate remarkable photo-induced conductance plasticity at both 633 and 980nm wavelengths. A dynamic vision system consisting of 20 × 20 optoelectronic neurons demonstrates remarkable capabilities in the precise detection and perception of various motions. Moreover, neural network computing systems have been built as visual motion perceptron to identify target object movement. The recognition accuracy of dual-wavelength fused images for various motion trajectories has experienced a remarkable enhancement, transcending the previous level of less than 80% to impressive values exceeding 99%.

A Tutorial on the Strong Gravity Effects in Black Hole X-Ray Spectra

This is a tutorial on the strong gravity effects (motion of massive and massless particles in a curved spacetime, evaluation of redshift factors, estimate of physical quantities in different reference frames, etc.) necessary to calculate the electromagnetic spectra of geometrically thin and optically thick accretion disks around black holes. The presentation is intentionally pedagogical, and most calculations are reported step by step. In the disk–corona model, the spectrum of a source has three components: a thermal component from the disk, a Comptonized component from the corona, and a reflection component from the disk. This tutorial reviews only the strong gravity effects, which can be decoupled from the physical processes involving the interaction between matter and radiation. The formulas presented here are valid for stationary, axisymmetric, asymptotically flat, circular spacetimes, so they can be potentially used for a large class of black hole solutions.

Hybrid Terahertz Emitter for Pulse Shaping and Chirality Control

AbstractTerahertz (THz) radiation (0.3 to 30 THz) fills the crucial gap between the microwave and infrared spectral range. THz technology is important for applications ranging from imaging to telecommunication to biosensing, but these applications often require precise control and manipulation of the THz frequency and polarization state, which typically requires modulators external to the THz source. A hybrid THz emitter that overcomes this limitation by integrating two THz emitters into a single device to enable pulse shaping and chirality control of the emitted radiation without any external components is demonstrated. The two sources are a spintronic emitter (SE) and a semiconductor photoconductive antenna (PCA). The two emitters respond independently to external parameters: the PCA is controlled by the applied bias voltage, while the SE is controlled by the applied magnetic field. Moreover, a dual‐wavelength excitation scheme allows for control of the relative time delay between the THz emission from each constituent. These properties of the hybrid emitter enable precise control of the mixing of the two signals to control the frequency, polarization, and chirality of the overall THz radiation. This on‐chip hybrid emitter thus provides a powerful platform for engineered THz radiation with wide‐ranging potential applications.

High-temperature measurements of acetylene VUV absorption cross sections and application to warm exoplanet atmospheres

Most observed exoplanets have high equilibrium temperatures (T$_ eq $ > 500 K). Understanding the chemistry of their atmospheres and interpreting their observations requires the use of chemical kinetic models including photochemistry. The thermal dependence of the vacuum ultraviolet (VUV) absorption cross sections of molecules used in these models is poorly known at high temperatures, leading to uncertainties in the resulting abundance profiles. The aim of our work is to study experimentally the thermal dependence of VUV absorption cross sections of molecules of interest for exoplanet atmospheres and provide accurate data for use in atmospheric models. This study focuses on acetylene (C$_ $H$_ We measured absorption cross sections of C$_ $H$_ $ at seven temperatures ranging from 296 to 773 K recorded in the 115-230 nm spectral domain using VUV spectroscopy and synchrotron radiation. These data were used in our 1D thermo-photochemical model, to assess their impact on the predicted composition of a generic hot Jupiter-like exoplanet atmosphere. The absolute absorption cross sections of C$_ $H$_ $ increase with temperature. This increase is relatively constant from 115 to 185 nm and rises sharply from 185 to 230 nm. The abundance profile of C$_ $H$_ $ calculated using the model shows a slight variation, with a maximum decrease of 40<!PCT!> near 5 times 10$^ $ bar, when using C$_ $H$_ $ absorption cross sections measured at 773 K compared to those at 296 K. This is explained by the absorption, higher in the atmosphere, of the actinic flux from 150 to 230 nm due to the increase in the C$_ $H$_ $ absorption in this spectral range. This change also impacts the abundance profiles of other by-products such as methane (CH$_ $) and ethylene (C$_ $H$_ We present the first experimental measurements of the VUV absorption cross sections of C$_ $H$_ $ at high temperatures. Similar studies of other major species are needed to improve our understanding of exoplanet atmospheres.

Contribution of interference to the magneto-optical transverse Kerr effect in white light

Objectives. When measuring the transverse Kerr effect on thin-film structures, interference effects have a great influence on the result obtained. In conference presentations, some researchers have reported on the use of white light in experiments. In their opinion, despite the thickness of the studied layers being much less than the wavelength of light, white light can help avoid interference effects and/or resonant excitation of plasmon waves. The aim of the present work is to verify the validity of such statements using simulation.Methods. In order to solve this problem, the method of computer simulation was used. A numerical solution of equations was compiled for a model structure for various thicknesses and materials of layers.Results. The simulation results show that interference effects in different parts of the spectrum when using white light sources do not neutralize each other. The magnitude of the effect is affected not only by the thickness of the structure layers, but also by the shape of the source emission spectrum, as well as the sensitivity curve of the photodetector. In this case, the output of the measured value of the effect to a plateau at relatively large thicknesses of the magnetooptical film is due to the light being absorbed in the thickness of the magneto-optical film and is negligibility of the back reflection of light from the substrate.Conclusions. The presented technique takes into account the influence of interference effects when measuring the equatorial Kerr effect in white light or using other sources having a wide spectral range, thus improving the interpretation of experimental results. The results are relevant to the development and research of the physical foundations for creating new and improving existing devices in micro-, nano-, and solid-state electronics, as well as quantum devices, including optoelectronic devices and converters of physical quantities.

Computational investigation of the phase stability, electronic, optical, phonon spectrum, and elastic behavior of layered perovskites Ca2XO4 (X = Zr, Hf) for optoelectronic applications.

A significant class of solid-state materials, Ruddlesden-Popper (RP) perovskites are well-known for their rich chemical compositions that make them excellent electrocatalysts. Therefore, in this work, we conduct thorough analysis of RP perovskites, specifically Ca2XO4 (X = Zr, Hf). We delve into the structural, electronic, optical, and mechanical properties presenting their insights for the first time. Our investigations reveal that Ca2XO4 (X = Zr, Hf) exhibits stable tetragonal phase structures, with energies (E0) of - 10,522.93eV and - 33,520.14eV, respectively. The calculated in terms of the ground state determines to possess distinct values such as - 4.79 eV/atom for LiScTe2 and - 3.95 eV/atom for Ca2ZrO4 and Ca2HfO4. Notably, the semiconductor characteristics of Ca2ZrO4 and Ca2HfO4 are underscored by their respective wide direct band gap of 5.02eV and 5.30eV. Then, we discuss the optical parameters encompassing the dielectric function, absorption coefficient, optical conductivity, refractive index, and energy loss function. is described as ductile, whereas is defined as brittle. Our outcomes underscore remarkable ability of these materials to absorb ultraviolet radiation from the electromagnetic spectrum, positioning them as promising candidates for optoelectronic applications. We made these calculations by employing first-principles approach rooted in density functional theory (DFT) and utilizing the Perdew-Burke-Ernzerhof-Generalized Gradient Approximation (PBE-GGA) and Tran and Blaha-modified Becke-Johnson (TB-mBJ) functional within the WEIN2K framework. In this framework, Kramers-Kronig relations are used to obtain crucial optical parameters. Mechanical behavior is assessed by employing Voigt-Reuss-Hill approximation (VRH) fulfilling the Born's criteria which emphasizes that these materials are equally appropriate for a broad range of mechanical applications.

The effects of strain and interface engineering on the PbS/PbSe/CsPbI3 heterojunction

Abstract This paper investigates the PbS/PbSe/CsPbI3 heterojunction based on first-principles calculations within the framework of density functional theory and demonstrates the effects of different strains on the structural, electronic, optical properties. PbS/PbSe, PbSe/CsPbI3 and PbS/CsPbI3 all possess relatively low lattice mismatch rates (2.3%, 2.4% and 4.6%) and similar octahedral structures. The PbS/CsPbI3 heterojunction reduces carrier transfer losses between different materials. By serving as the functional layer, PbSe can alter the electron–hole recombination losses at the heterostructure interface, broaden the spectral response range, and change the electronic density around the atoms at the heterostructure interface. All three heterojunctions are direct band gap semiconductors (ΔEg: PbS/PbSe-PbSe/CsPbI3-PbS/CsPbI3, 0.632–0.856–0.523 eV). The spectral comparison shows that PbS/PbSe/CsPbI3 > PbSe/CsPbI3 > CsPbI3, indicating that PbS/PbSe/CsPbI3 exhibits superior stability, charge density transfer, and optical performance with a redshift in absorption spectra. Additionally, the band gap and optical properties of PbS/PbSe/CsPbI3 can be adjusted by applying strain, thereby affecting its optical absorption intensity. This work provides a theoretical foundation for improving the performance of PbS/PbSe/CsPbI3 heterojunction as visible-near infrared optoelectronic materials.

Recent Developments in Applications of G-CuO Nanocomposites for Photocatalytic Dye Removal

Abstract The extensive application of synthetic dyes across industries poses significant environmental challenges, particularly concerning water quality degradation. Regarding the possible solutions, copper oxide (CuO) stands out as a feasible candidate. Being a p-type Nano-heterogeneous semiconductor with a bandgap of 1.2–2.71 eV, CuO is a reasonable choice and widely studied photocatalyst for addressing such challenges. When the wavelength exceeded the UV-visible region, its functionality showed deterioration. At the same time, there are difficulties associated with reproducibility and reusability, as well as rapid electron-hole recombination, which prevent the widespread application of this technology within this spectral range. In an attempt to eliminate this defect, researchers have been investigating strategies to activate CuO under visible light, with one promising approach being carbon nanomaterials such as graphene to form carbon-CuO composites. The unique properties of graphene, i.e., its large surface area and excellent electron mobility, make it a remarkable candidate for the enhancement of CuO photoactivity. This study highlighted the recent progress in the synthesis of graphene-based CuO photocatalysts, with the main characteristic of extending the light absorption capacity of CuO into the visible spectrum. It reveals achievements in material innovations and applications, with a focus on photocatalytic dye degradation. These breakthroughs are a sign that the field is growing in popularity and is evolving.

Phase-coded coherent microwave pulse generation based on an actively mode-locked optoelectronic parametric oscillator

An approach for generating phase-coded coherent microwave pulse trains at high frequencies is proposed and demonstrated based on an actively mode-locked optoelectronic parametric oscillator (AML-OEPO), where an electrical mixer is inserted into the cavity of an optoelectronic oscillator (OEO) to achieve both mode locking and parameter oscillation. The driving signal applied to the mixer is a low-frequency sinusoidal signal with voltage polarity coding, where the frequency is the same as the free spectral range (FSR) of the OEO cavity, and the duration of each voltage polarity coding bit is identical to the loop delay. As a result, phase-coded coherent microwave pulse trains can be generated, where the pulse interval is equal to the loop delay due to the active mode locking effect, and the phase coding period is equal to a multiple integer of the loop delay due to parameter oscillation. The enhancement of the signal period and the highly coherent characteristic are beneficial for breaking the contradiction between unambiguous detection range and ranging resolution in pulse radars. In the experiment, phase-coded microwave pulse trains with either 13-bit barker codes or 7-bit M codes are generated at 15.026 GHz. The autocorrelation calculation result of the phase-coded microwave pulse train with 13-bit barker codes shows a high peak-to-sidelobe ratio, verifying high coherence.

Silicon-based light-emitting transistor with Ge(Si) nanoislands embedded in a photonic crystal: Control of the spectrum and spatial distribution of the emission

Light-emitting transistors (LETs) represent the next step in the development of light-emitting diodes (LEDs), offering additional control over emission. In this work, the transport properties and spatial distribution of electroluminescence (EL) in the spectral range of 1.2–1.7 μm were studied for lateral p+-i-n+ LEDs based on silicon-on-insulator structures with self-assembled Ge(Si) islands embedded in photonic crystals. It is shown that due to the low mobility of holes and their effective trapping in the islands, the maximum EL yield is observed at the i/p+ junction of the LED. It is demonstrated that the sign and magnitude of the bias voltage applied to the substrate (to the gate) have a significant influence on the transport and emission properties of the LEDs with Ge(Si) islands, turning them into LETs. In particular, applying a negative gate voltage shifts the position of the maximum emission region from the i/p+ to the i/n+ junction of the LET, which is related to the formation of a hole conductivity channel near the buried oxide layer. The embedding of a specially designed photonic crystal in the i-region of the LET makes it possible to manage the spectral properties of the near-IR emission by changing the sign of the gate voltage. The results obtained may be useful for the future development of optoelectronic devices.

Archetypal crop trait dynamics for enhanced retrieval of biophysical parameters from Sentinel-2 MSI

We present a new method for estimating biophysical parameters from Earth Observation (EO) data using a crop-specific empirical model based on the PROSAIL Radiative Transfer (RT) model, called an ‘archetype’ model. The first-order model presented uses maximum biophysical parameter magnitude, phenological and soil parameters to describe the spectral reflectance (400–2500 nm) of vegetation over time. The approach assumes smooth variation and archetypical coordination of crop biophysical parameters over time for a given crop. The form of coordination is learned from a large sample of observations. Using Sentinel-2 observations of maize from Northeast China in 2019, we map reflectance to biophysical parameters using an inverse model operator, synchronise the parameters to a consistent time frame using a double logistic model of LAI, then derive the model archetypes as the median value of the synchronised samples. We apply the model to estimate time series of biophysical parameters for different cereal crops using an ensemble framework with a weighted K-nearest neighbour solution, and validate the results with ground measurements of different crops collected near Munich, Germany in 2017 and 2018. The results show R values greater than 0.8 for leaf area index (LAI) and leaf brown pigment content (Cbrown), with an RMSE of 0.94 m2/m2 for LAI and 0.15 for Cbrown. The chlorophyll content (Cab) and canopy water content (CCw) were retrieved at a higher level of accuracy, with R values around 0.9 and an RMSE of 6.59μg/cm2 for Cab and 0.03 g/cm2 for CCw. Comparison of forward-modelled hyperspectral reflectance with independent ground measures shows that the retrieved parameters account for 90% of the variation in canopy reflectance, with an overall RMSE of around 0.05 in reflectance units. The retrievals for all terms are mostly within 1σ when measurement and prediction uncertainty are taken into account, except for some early and late season issues in leaf and canopy water due to the complexity of canopy structure and understory during these periods. The approach provides a new form of constraint for the simultaneous estimation of biophysical parameters from EO and greatly reduces the rank of the problem. It is suitable for monitoring crop conditions where biophysical parameters vary smoothly over time consistently with each archetype form. The approach can be refined for other canopy types and canopy representations and could provide strong constraints on expected smoothly-varying canopy features to aid in the interpretation of EO signals across different regions of the electromagnetic spectrum.

The Impact of Water Clouds on the Prospective Emission Spectrum of Teegarden’s Star b as Observed by LIFE

Nontransiting terrestrial planets will be accessible by upcoming observatories of which LIFE is an example. Planet b orbiting Teegarden’s Star is one of the optimal targets for such missions. We use a one-dimensional atmospheric model with real gas radiation, a multispecies pseudo-adiabatic convection-condensation scheme, and a water cloud scheme to estimate the impact of the cloud coverage on the emission spectrum of the target, as well as to assess how sensitive LIFE could be to changes in outgoing flux caused by these clouds. Though the emergent flux decreases with a higher cloud coverage, it does not decrease by more than 1 order of magnitude as the coverage increases from 0% to 90%. This allows LIFE to retain a high sensitivity to the cloud cover fraction for wavelengths longer than 7 μm. In this spectral range, with at least 1 bar of N2, LIFE is able to distinguish cloud cover fractions as small as 10% given an integration time of 24 hr, and yields much better precision with a week-long integration. An integration time of 1 week also allows the resolution of local variations in spectral flux, which can lead to easier molecule identification. This ability remains if the planet is a CO2-dominated Venus analog. Partial pressures of N2 lower than 1 bar may create a degeneracy with the cloud cover fraction. LIFE shows promising potential for detecting and characterizing atmospheres even with a high cloud coverage, and retaining a fine sensitivity to relatively small differences in cloud cover fractions.

Removal of tetracycline using an ultrastable Pt-decorated-BNCB photocatalyst under efficient solar-driven conditions

The pursuit of optimizing the photocatalytic performance of the novel perovskite-like Bi4NbO8X materials remains a vibrant area of research. In this paper, we report the successful synthesis of the Bi4Nb4O8Cl0.935Br0.065 (BNCB) composite photocatalyst, loaded with Pt nanoparticles, utilizing a combination of solid-state reaction and sodium borohydride reduction methods. Notably, the surface plasmon resonance (SPR) effect exhibited by Pt broadened the spectral response range, while the Schottky junction formed at the Pt/BNCB interface significantly accelerated the separation of photogenerated electron-hole pairs and facilitated the swift migration of photogenerated electrons towards Pt. Experimental outcomes underscore the superior photocatalytic degradation efficacy of the Pt/BNCB composite towards tetracycline (TC), achieving a degradation rate of up to 67%, significantly outperforming pure BNCB. Pt/BNCB exhibits excellent photocatalytic degradation and excellent stability in various pH and ionic environments. Collectively, this work presents a novel approach for designing highly efficient and stable perovskite-type photocatalytic materials, holding immense potential for applications in environmental remediation.

Plasmon and N-vacancy synergistically enhanced tubular carbon nitride-based S-scheme heterojunction photocatalyst with one stone five birds function: Pathways, DFT calculation and mechanism insight

From the perspectives of innovation and broad-spectrum, tubular carbon nitride-based photocatalyst, viz., Ag/AgI/g-C3N4 S-scheme heterojunction photocatalyst, with enhancement of nitrogen vacancy and localized surface plasmon resonance (LSPR) effect is reasonably devised and manufactured via combining hydrothermal, calcination and photo-reduction techniques. The optimal specimen displays high photocatalytic activity in removal of dyes (such as crystalline violet, 100.00 %/60 min), antibiotics (such as levofloxacin, 88.72 %/50 min) and Cr6+ (100.00 %, 30 min), photocatalytic hydrogen evolution (1023.3 μmol h−1 g−1) and H2O2 generation (866.2 μmol h−1 g−1), achieving broad-spectrum natures, viz., realizing the function of “one stone five birds”. The broad-spectrum natures are attributed to the synergisms of nitrogen vacancy, LSPR effect of Ag, hollow tube structure and S-scheme heterojunction, which facilitate the separation and migration of photo-generated carriers and inject “hot electrons” generated by Ag into the conduction band of Ag/AgI/g-C3N4, increase the specific surface area and broaden the spectral response range. Further, the degraded intermediates of crystalline violet and levofloxacin and possible degradation pathways are rationally advanced by the aid of LCMS spectra, and synergistically enhanced photocatalytic mechanism of Ag/AgI/g-C3N4 hollow tube S-scheme heterojunction is confirmed based upon a series of sound experiments, fs-TA spectra, in-situ XPS and DFT calculation, etc.