Absorption Band Edge Research Articles

Characterization and linear / nonlinear optical aspects of polyaniline (PANI) films incorporated with Ethylenediamine for low-cost limiting optical technologies

Polymer composite combined film with Polyaniline (PANI) and Ethylenediamine (EDA) were successfully synthesized via the spin coating technique on a glass substrate followed by different thermal annealing degrees and times. Successful incorporation of EDA into the PANI polymer matrix and the effect of the annealing temperature have been demonstrated by XRD, FTIR, FESEM and TEM. Using UV–Vis optical spectroscopy, we determine the absorption coefficient, band edge, and Urbach energy. The effects of different annealing temperatures and times on linear/nonlinear optical characteristics were investigated. The band gap of EDA-doped PANI films is reduced with the different thermal annealing from 3.43 eV to 3.19 eV, while the Urbach tail of the 100 °C/4h film which is 0.492 eV was decreased to 0.469 eV for 150 °C/1h sample. However, the absorbance and optical conductivity were both increased. Besides, the optical limiting effect assesses their potential to mitigate intense light. It was found from the study that for green wavelength 100 °C/4h film decreases the input power by 16.5 % whereas the 150 °C/1h sample shows superior limiting behavior of 99.96 %. It has been found that thermal annealing of the EDA-doped PANI films enhances the synthetic composite's optical characteristics, making the 150 °C/1h sample of EDA-doped PANI films appropriate for utilization in both energy applications and optoelectronics.

Narrow Band Gap Base Metal Double Perovskite Oxides Through Copper Doping of Ba2Ca0.66Nb1.33O6

This work examines the influence of copper doping on the structure, optoelectronic properties, and photocatalytic performance of transition metal double perovskite oxides of the Ba2Ca0.67Nb1.33O6 (BCN) family. A solid-state synthesis method was used to achieve partial substitution of Cu2+ in the Nb5+ site (Ba2Ca0.67Nb1.33-xCuxO6-δ, x = 0.05, 0.13, 0.26) and Ca2+ site (Ba2Ca0.67-xCuxNb1.33O6-δ, x = 0.13). The incorporation of copper in BCN resulted in significant changes in the structure and optoelectronic properties. Major differences were observed when Cu atoms occupied the Nb-site versus the Ca-site. The parent compound and Ca-site doped compounds crystallized in a P3 1 space group while Nb-site doped compounds showed increasing Fm3 mixed phase character. Cu doping resulted in a dramatic shift of the absorption band edge towards the visible region. Ca-site doping resulted in a primary band edge shift from 3.8 eV to 2.1. For the Nb-site doped compounds, the primary band-edge remained at 3.8 eV but a secondary band-edge appeared which progressively shifted to smaller energies as Cu doping increased. Ba2Ca0.67Nb1.20Cu0.13O6-δ and Ba2Ca0.67Nb1.07Cu0.26O6-δ exhibited strong absorption of near-infrared photons of wavelength well beyond 800 nm. The double perovskite oxides were utilized as photoanodes for photoelectrochemical water splitting, exhibiting both a visible photoresponse (until wavelengths as low as 520 nm) and good photochemical stability. This work showcases the possibility of forming new low band gap multi-element inorganic semiconductor oxides constituted entirely of base metals and oxygen.

In-Situ comparative study of photo-induced charge behavior in single-perovskite Cs3Bi2Br9 and double-perovskite Cs2AgBiBr6

While organic-inorganic lead halide perovskites excel in optoelectronic applications, their use is limited by toxicity and degradation. Consequently, lead-free alternatives like Cs2AgBiBr6, offering greater stability and diverse applications, have been investigated. However, the fundamental structural, optical, and electronic properties of Cs2AgBiBr6 remain insufficiently understood. In this study, we compared the exciton dynamics and photo-induced charge separation in Cs3Bi2Br9 and Cs2AgBiBr6 films using in-situ surface techniques. Both materials display similar surface photovoltage (SPV) peaks in the 450–500 nm range, supporting the hypothesis of Bi 6s-6p orbital transitions in distorted [BiBr6]3− structures. Although many theories propose the presence of self-trapped excitons (STE) in bismuth-based perovskites, sufficient evidence has been lacking. Our observation of a significant redshift in the SPV peak compared to the band edge absorption peak supports STE hypothesis, with Cs2AgBiBr6 showing a more pronounced redshift due to its more complex electronic structure and stronger electron-phonon coupling. Additionally, we observed that Cs2AgBiBr6 exhibits superior charge separation efficiency compared to Cs3Bi2Br9. Notably, Cs2AgBiBr6 shows significantly shorter rise times, indicating more rapid photogenerated charge separation. However, both materials exhibit similar fall times, suggesting comparable charge recombination rates. Light-chopping-frequency dependent SPV measurements further reveal that Cs2AgBiBr6 has a higher charge separation rate than Cs3Bi2Br9. These findings underscore the potential of bismuth-based perovskites for optoelectronic applications and highlight the importance of a comprehensive understanding of their structure-property relationships.

A Class of Heptaphyrins with NIR Absorption Modulated by Metal Coordination and Nucleophilic Substitution.

The intensive interest in expanded porphyrins can be attributed to their appealing photoelectric and coordination behavior. In this work, an N-confused heptaphyrin 1 was synthesized by an acid-catalyzed [3+4] condensation reaction. The introduction of an N-confused pyrrolic unit into the heptaphyrin macrocycle led to the formation of a figure-eight-like conformation with nonsymmetrical "NNNN" and "NNNC" coordination cavities employable for bimetallic coordination. As a result, chelation of 1 with Zn(II) and Cu(II) afforded mono-Zn(II) complex 2 and bis-Cu(II) complex 3, respectively, with the metal atoms exhibiting distorted square-planar geometries. In complex 3, an oxygen atom is attached to the α-C atom of N-confused pyrrole D, and thus the N and C atoms of ring D participate in coordination within the two cavities. Interestingly, treatment of 1 with Cs2CO3 in MeOH resulted in regioselective substitution of all the seven para-F atoms in the meso-C6F5 groups as well as the α-H of ring D by eight methoxy moieties. Complex 3 displays a red-shifted absorption band edge of ca. 2200 nm, compared to that of ca. 1600 nm observed for 1. This work provides an example of incorporating an N-confused pyrrole to construct expanded porphyrins with distinctive coordination behavior and tunable NIR absorption.

Fine-Tuning the Microstructure and Photophysical Characteristics of Fluorescent Conjugated Copolymers Using Photoalignment and Liquid-Crystal Ordering.

Replicating the microstructural basis and the near 100% excitation energy transfer efficiency in naturally occurring light-harvesting complexes (LHCs) remains challenging in synthetic energy-harvesting devices. Biological photosynthesis regulates active ensembles of light-absorbing and funneling chlorophylls in proteins in response to fluctuating sunlight. Here, use of long-range liquid crystal (LC) ordering to tailor chain orientation and packing structure in liquid crystalline conjugated polymer (LCCP) layers for bio-mimicry of certain structural basis and light-harvesting properties of LHCs is reported. It is found that long-range orientational ordering in an LC phase of poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) copolymer stabilizes a small fraction of randomly-oriented F8BT nanocrystals dispersed in an amorphous matrix of F8BT chains, resembling a self-doped host-guest system whereby excitation energy funneling and photoluminescence quantum efficiencies are enhanced significantly by triggering 3D donor-to-acceptor Förster resonance energy transfer (FRET) and dominant intrachain emission in the nano-crystal acceptor. Further, photoalignment of nematic F8BT layers is combined with LC orientational ordering to fabricate large-area-extended monodomains exhibiting >60% crystallinity and ≈20nm-long interchain packing order. Remarkably, these monodomains demonstrate strong linearly polarized emission, whilst also promoting a new band-edge absorption species and an extra emissive interchain excited state as compared to the non-aligned films.

The effect of SiO2 crystallization in enhancing the luminescence of Dy3+-Sm3+ co-doped glass ceramics for cool white light application.

The present work investigates the structural and luminescence behaviour of Dy3+-Sm3+ co-doped glass ceramics obtained through heat treatment of precursor glasses. The growth of SiO2 polycrystalline particles and evolution of these crystallites in the glass domain are witnessed via XRD and FESEM study. The presence of network vibrational bands, hydroxyl groups and the increased quantity of bridging oxygens (BOs) in glass ceramics are analysed through FTIR spectroscopy study. The absorption study (UV-Visible-NIR) showed the possible electronic transitions of Dy3+ and Sm3+ ions. The red shift in the absorption band edges and the lower bandgap values are obtained as a result of improved heat treatment in glass ceramics. Emission studies show the enhanced luminescence intensity of glass ceramics under 350 and 402 nm excitations. Decay measurement of glass ceramics showed the improved lifetimes of Dy3+ and Sm3+ ions to have appeared in microseconds (×10-6s). The colour characteristics of glass ceramics analysed using CIE colour chromaticity diagram and correlated colour temperature (CCT) values suggest the neutral to cool white light emissions. Therefore, prepared glass ceramics with SiO2 polycrystalline phase are considered to be suitable materials in cool white LEDs applications.

Comparison of electronic structures, thermodynamic, optical and mechanical properties of MgB2 and MgMB4(M=Al, Pb, W) based on first-principles

As an important superconducting material, MgB2 has a wide range of applications in electronics and communication fields. The optimization of its properties has been a hot research topic. In this paper, it uses first-principles calculations to delve into the impact of doping Type-I superconducting elements M (M = Al, Pb, W) on the properties of MgB2. The main focus is on exploring improvements in thermodynamic, optical and mechanical properties in conjunction with the analysis of electronic properties. For thermodynamic properties, MgPbB4 demonstrates significant variation in entropy and free energy as temperature increases, reaching 356.84 KJ/mol and −411.46 KJ/mol, respectively, at 2000 K. Regarding optical properties, the absorption band edge disappears and the range widens with the introduction of M elements. Specifically, MgWB4 exhibits the highest reflectivity R (0) and static dielectric constant ε1 (0) in the [001] direction, measured at 0.49 and 32.2, respectively. In terms of mechanical properties, the elastic modulus of MgAlB4 and MgWB4 enhances notably with B/G ratios less than 1.75, indicating their brittleness. MgWB4, in particular, stands out with the highest elastic modulus and the weakest elastic anisotropy AU (0.703), exhibiting a spatial distribution nearer to spherical. Conversely, MgPbB4 transforms the material into a ductile one, with reduced elastic modulus and the strongest anisotropy AU (4.963). This study can provide a more comprehensive perspective for the future design of MgB2-based materials.

Copper doped hybrid 2D ZnO-stearic acid nanocomposite for boosting photocatalytic degradation of organic pollutants under simulated solar light

This study explores the enhancement of photocatalytic performance in 2D ZnO-stearic acid (SA) composites through copper (II) doping. Materials containing 1–10 mol% Cu (II) were synthesized by coprecipitation and characterized using X-ray photoelectron spectroscopy, electron paramagnetic resonance, UV–visible and vibrational spectroscopies, as well as X-ray diffraction. These analyses confirmed the formation of single-phase composites with structures resembling the ZnO-SA precursor, but exhibiting discrete Zn/Cu doping, forming Zn1-xCuOx-SA materials. Scanning electron microscopy and Energy dispersive X-ray spectroscopy analysis revealed layered structure and the elemental compositions of the samples. High-resolution transmission electron microscopy (HR-TEM) images confirm the layered morphology of the Zn0.95Cu0.05O-SA sample, underscoring its two-dimensional material characteristics. Absorption band edge of the undoped hybrid ZnO is centered in the UVA zone, while copper-doped samples expanded into the visible range. Photoluminescence (PL) spectra exhibit multiple emission peaks related to defects within ZnO host. An intensity slight decrease in PL intensity is observed with increasing copper concentration, indicated a low recombination rate. Photoelectrochemical testing showed that Cu doping reduces charge recombination and increases current density, thereby improving photocatalytic degradation of pollutants such as indigo carmine and 4-chlorophenol under simulated sunlight. The optimally doped Zn0.95Cu0.05O-SA displayed significant efficiency improvements, degrading contaminants up to four times faster than the undoped composite and maintaining consistent performance over multiple cycles. Additional testing linked these photocatalytic improvements to enhanced charge separation and electron/hole transfer facilitated by Cu2+ ions, thereby boosting photocatalytic activity.

Spectator Exciton Effects in Nanocrystals III: Unveiling the Stimulated Emission Cross Section in Quantum Confined CsPbBr3 Nanocrystals.

Quantifying stimulated emission in semiconductor nanocrystals (NCs) remains challenging due to masking of its effects on pump-probe spectra by excited state absorption and ground state bleaching signals. The absence of this defining photophysical parameter in turn impedes assignment of band edge electronic structure in many of these important fluorophores. Here we employ a generally applicable 3-pulse ultrafast spectroscopic method coined the "Spectator Exciton" (SX) approach to measure stimulated-emission efficiency in quantum confined inorganic perovskite CsPbBr3 NCs, the band edge electronic structure of which is the subject of lively ongoing debate. Our results show that in 5-6 nm CsPbBr3 NCs, a single exciton bleaches more than half of the intense band edge absorption band, while the cross section for stimulated emission from the same state is nearly 6 times weaker. Discussion of these findings in light of several recent electronic structure models for this material proves them unable to simultaneously explain both measures, proving the importance of this new input to resolving this debate. Along with femtosecond time-resolved photoluminescence measurements on the same sample, SX results also verify that biexciton interaction energy is intensely attractive with a magnitude of ∼80 meV. In light of this observation, our previous suggestion that biexciton interaction is repulsive is reassigned to hot phonon induced slowdown of carrier relaxation leading to direct Auger recombination from an excited state. The mechanism behind the extreme slowing of carrier cooling after several stages of exciton recombination remains to be determined.

The Impact of Partial Carrier Confinement on Stimulated Emission in Strongly Confined Perovskite Nanocrystals.

Semiconductor lead halide perovskites are excellent candidates for realizing low threshold light amplification due to their tunable and highly efficient luminescence, ease of processing, and strong light-matter interactions. However, most studies on optical gain have addressed bulk films, nanowires, or nanocrystals that exhibit little or no size quantization. Here, we show by means of a multitude of optical spectroscopy methods that small CsPbBr3 nanocrystals (NCs) exhibit a progressive red shift of the band-edge transition upon addition of electron-hole pairs, at least one carrier of which occupies a 2-fold degenerate, delocalized state in agreement with strong confinement. We demonstrate that this combination results in a threshold for biexciton gain, well below the limit of one electron-hole pair on average per NC. On the other hand, both the luminescent lifetime and the optical Stark effect of 4.7 nm CsPbBr3 NCs indicate that the oscillator strength of the band-edge transition is considerably smaller than expected from the band-edge absorption. We assign this discrepancy to a mixed confinement regime, with one delocalized and one localized charge carrier, and show that the concomitant reduction of the oscillator strength for stimulated emission accounts for the surprisingly small material gain observed in small NCs. The conclusion of mixed confinement aligns with studies reporting small and large polarons for holes and electrons in lead halide perovskite nanocrystals, respectively, and creates opportunities for understanding multiexciton photophysics in confined perovskite materials.

Synthesis, characterization and performance evaluation of a novel flower-like Zn[sbnd]Zr MOF/FeWO4/BiOBr/Ti photoanode with type II heterojunction and visible light response

The performance of a photocatalytic fuel cell (PFC) depends on its photoelectrode. In this work, a novel three-dimensional flower-like hierarchical photoanode ZnZr MOF/FeWO4/BiOBr/Ti was synthesized, characterized and applied in PFC to degrade rhodamine B and generate electricity simultaneously. The characterization results of XRD, SEM, EDS, FI-IR, DRS, and XPS show that the photoanode was successfully prepared. The loading of FeWO4 and ZnZr MOF widened the nanosheet spacing of BiOBr, which enhanced the light absorption intensity, broadened the light absorption band edge from 467.6 nm to 490.2 nm, and increased the photocurrent density from 0.0149 mA/cm2 to 0.156 mA/cm2. The maximum photocurrent density, maximum power density, degradation rate, and FF of the PFC with the prepared photoanode were respectively 0.256 mA·cm−2, 22.65 μW·cm−290.48 % (1 h), and 0.216, which were far higher than those of PFCs with mono and binary photoanodes. The strong photocatalytic performance of the photoanode is attributed to the type II heterojunction formed between BiOBr and FeWO4, which helps to separate electron-hole pairs. The main reactive materials responsible for degrading rhodamine B are h+ and ·O2-. This research provides a new idea for developing an efficient visible light response photoanode.

Impact of Cu2+ precursor on physical and photoelectrochemical properties of electrodeposited nanostructured CuS thin films for biosensor applications

Nanostructured CuS films were synthesized on FTO substrates employing low-cost electro deposition technique. XRD, Raman, SEM, UV–visible spectroscopy, photocurrent, PL, Mott-Schottky, and electrochemical impedance spectroscopy (EIS) measurements were used to examine physical and photoelectrochemical properties of samples. XRD results indicated that CuS films have hexagonal crystal structure where the crystallite size raises from 32 to 53 nm with increasing the Cu2+ molarity. Raman results displayed two peaks at 270 and 450 cm−1 that related to A1g transverse optical mode (TO) and A1g longitudinal optical (LO) mode for the vibrations of the S–S stretching and Cu–S bonds, respectively. SEM images displayed that fabricated CuS cover the substrate surface entirely, where grains are distributed uniformly with increasing the Cu+2 molarity. UV–visible measurements exhibited an absorption band edge between 450 and 550 nm as a characteristic of CuS films direct band gap. PL results presented strong blue-green emission at about 500 nm for CuS thin films. The photocurrent studies demonstrated that the CuS films are p-type semiconductors where the current density increases from 0.8 mA/cm2 to 1.1 mA/cm2 with the Cu2+ molarity increasing. The EIS analysis confirmed that charge transfer resistance reduces with increasing molarity. Mott- Schottky measurements established that carrier concentrations and the flat band varied from 5 × 1019 to 6.7 × 1019 cm−3 and from 1.1 to 0.75V, respectively. The fabricated CuS film was tested as glucose biosensor where a fast response and higher stability were noticed. Our results indicated that nanostructured CuS films are gifted candidates for optoelectronics applications especially biosensors.

Single‐Step Chemical Vapor Deposition of Methyl Ammonium Lead Halide Perovskite for p–i‐n Solar Cells

AbstractMetal halide perovskite solar cells being one of the fastest emerging technologies for renewable energy still has to become more industry friendly in a way that will allow using it for thin film modules or tandems with conventional silicon devices. The simplest way to achieve this is to use chemical vapor deposition (CVD) technique for tandem production. In this work, we show a method for a single step production of MAPbI3 films in a simple two‐zone CVD reactor from lead diacetate and methyl‐ammonium iodide powders. Obtained films show highly ordered cubic MAPbI3 phase with a thickness of 400–500 nm, good photoluminescence response and absorption band edge similar to spin‐coated film. We used those films to produce p‐i‐n solar cells with ITO/NiO/MAPbI3/C60/Cu structure. The best cell showed negligible 0.23 % PCE right after the manufacturing but significantly improved to 5.5 % PCE after 8 hours of storage in the dark. The main limiting factor affecting the efficiency is low current density, which we attribute to non‐optimized growth conditions; however, our approach is a first step to a single step CVD deposition of MAPbI3 on any type of substrates including texturized silicon subcells for better overall efficiency

Effect of annealing temperature on physical properties and photoelectrochemical behavior of electrodeposited nanostructured NiO thin films for optoelectronic applications

Our paper used a low-cost electrodeposition technique to grow Nickel Oxide (NiO) thin films on fluorine-doped tin oxide (FTO) substrate. As-deposited films were annealed at different temperatures (350, 400, 450, and 500 °C). X-ray diffraction (XRD), Raman spectroscopy (RAM), scanning electron microscopy (SEM), UV–vis spectrophotometer, photoluminescence (PL), Cyclic voltammetry (CV), photocurrent (PC), electrochemical impedance spectroscopy (EIS), and Mott-Schottky analysis (MS) were used to study and investigate the effect of annealing temperatures on the structural, morphological, electrical, and optical properties of prepared thin films. XRD patterns proved the cubic phase of all NiO samples with the preferential orientation in (111) direction. SEM results showed that the grain size increased with increasing annealing temperature. The optical transmission was studied by a UV–vis spectrophotometer, where high transmittance for NiO thin films was found to vary in the range of 73–84 % in the visible wavelength region, depending on the annealing temperatures. At the same time, UV–visible measurements indicate an absorption band edge at 311 nm, mainly recognized as a characteristic direct band gap for prepared NiO. The optical gap calculated from the Tauc relation showed a decreasing trend from 3.97 to 3.86 eV with increasing annealing temperature from 300 °C to 500 °C. PL spectra of synthesized samples revealed two distinct emission peaks at around 400 nm and 490 nm. RAM analysis confirmed the presence of three characteristic peaks related to the vibration of Ni–O bonds. The NiO film annealed at 500 °C displays the highest specific capacitance value by CV analysis. The P-type conductivity of manufactured arrays and enhanced electrical properties were confirmed by PC, EIS, and MS analysis. The highest carrier concentration values (9.19 × 1018 cm−3) and flat band potential (0.82 V) were obtained for samples annealed at 500 °C. Our outcomes proved that NiO-500 °C thin films are ideal candidates for optoelectronic applications.

Environmental-Friendly Ag2S QD-Multilayer MoSe2 van Der Waals Heterostructure for High-Performance Broadband Photodetection.

Broadband photodetectors have drawn intensive attention owing to their wide application prospects in optical communication, imaging, astronomy, and so on. Two-dimensional transition-metal dichalcogenides (TMDs) are considered as highly potential candidates for photodetection applications, benefiting from their excellent photoelectric properties. However, most of the photodetectors based on TMDs suffer from low performance in the near-infrared (NIR) region due to the weak optical absorption efficiency near their absorption band edge, which severely constrains their usage for broadband optoelectronics. Here, by taking advantage of the high absorption coefficient and environment-friendly property of Ag2S quantum dots (QDs), the hybrid of multilayer MoSe2/Ag2S QDs is demonstrated with a high-performance broadband photodetection capability (532-1270 nm). The favorable energy band alignment of MoSe2/Ag2S QDs facilitates effective separation and collection of photogenerated carriers, and the heterostructure device exhibits significant enhancement of performance compared to the bare MoSe2 device. High responsivity, detectivity, and external quantum efficiency of 25.5 A/W, 1.45 × 1011 Jones, and 1070% are obtained at a low working voltage of 1 V under 980 nm illumination. The responsivity of the device can reach up to 1.2 A/W at 1270 nm wavelength, which is competitive to the commercial NIR photodetectors. Meanwhile, broadband imaging capability is demonstrated. Our work may open up a facile and eco-friendly approach to construct high-performance broadband photodetectors for next-generation compact optoelectronic applications.

FABRIKASI SEL SURYA BERBASIS MATERIAL PEROVSKIT MAPbI3 SEBAGAI SUMBER ENERGI TERBARUKAN

The increasing for energy need encourages all parties to develop alternative energy sources with the concept of renewable energy, which utilizes resources that are always available in nature, such as sunlight energy. The device that can convert sunlight into electrical energy is a solar cell. In this research, solar cells were made based on the MAPbI3 perovskite material as an active material which functions as an absorber to absorb photons of sunlight. The solar cell device was fabricated with the FTO/c-TiO2/mp-TiO2/MAPbI3/PTAA/Au device structure using the OSPD-FDC (one step precursor deposition-fast deposition crystallization) method. The UV-Vis characterization results show that the absorption area of MAPbI3 starts from the wavelength range of 325 nm to 800 nm and shows the presence of an absorption band edge which is a special characteristic of perovskite materials. Meanwhile, characterization of photovoltaic properties produces a power conversion efficiency value of 13% with Jsc, Voc and FF values of 23 mA/cm2, 1.1 V, and 54% respectively

Effect of natural non-metallic impurities on the electronic structure and optical properties of sphalerite ZnS

Impurity-bearing sphalerite is widely found in nature and plays a vital role in photocatalysis. A systematic theoretical study of the crystal structure, band gap and optical properties of ZnS containing Si, Se and P impurities, respectively, is carried out using density functional theory calculations. The results show that non-metallic atoms in the interstices narrow the ZnS bandgap, improving the electrical conductivity of sphalerite. Analysis of the optical properties reveals that ZnS containing non-metallic impurities produces light absorption at higher energies. Meanwhile, the presence of all three impurities leads to a red shift in the absorption band edge of ZnS, which favors the extension of the light absorption range of sphalerite. The effect of the Si impurity is greater than that of the remaining two impurities, with the highest red shift. This research contributes to the application of sphalerite (ZnS) containing natural impurities in the field of new luminescent materials.

Preparation of TiO2/Ni‐NG Mesoporous Microspheres and Photocatalytic Hydrogen Evolution Properties

AbstractThe regulation of surface active sites and structures is a key factor affecting the performance of photocatalysts. In order to prepare monodisperse anatase TiO2 mesoporous microspheres with higher specific surface area, smaller pore size and particle size, a dual‐surfactant orientation assembly method was selected. Graphene (NG) was selected as a cocatalyst to compound with mesoporous TiO2 and nickel doping was performed on the cocatalyst to improve the photocatalytic hydrogen production activity of the semiconductor photocatalyst. Through proper regulation and rational design, the semiconductor photocatalyst with desired properties was prepared. SEM characterization of mesoporous titanium dioxide (TiO2/Ni‐NG) with graphene cocatalyst proved that TiO2 nanospheres have good monodispersion, and TiO2 nanospheres are well supported on graphene cocatalyst. The composite material belonged to mesoporous group with the pore size being mainly distributed between 10–20 nm. The loading of graphene and Ni‐NG cocatalyst increased the absorption band edge by 9 nm and 38 nm, respectively, and the band gap decreased by 0.07 eV and 0.16 eV, respectively. The selection of graphene as cocatalyst improved the hydrogen production activity of photocatalyst and nickel doping was very effective in the modification of graphene. For reaction time of 2.5 h, the H2 production of TiO2/Ni‐NG material reached 1.767 mmol/g which was 7.27 times that of TiO2/NG composite material.

Sensitive Thermochromic Behavior of InSeI, a Highly Anisotropic and Tubular 1D van der Waals Crystal.

Thermochromism, the change in color of a material with temperature, is the fundamental basis of optical thermometry. A longstanding challenge in realizing sensitive optical thermometers for widespread use is identifying materials with pronounced thermometric optical performance in the visible range. Herein, it is demonstrated that single crystals of indium selenium iodide (InSeI), a 1D van der Waals (vdW) solid consisting of weakly bound helical chains, exhibit considerable visible range thermochromism. A strong temperature-dependent optical band edge absorption shift ranging from 450 to 530 nm (2.8 to 2.3 eV) over a 380 K temperature range with an experimental (dEg/dT)max value extracted to be 1.26 × 10-3 eV K-1 is shown. This value lies appreciably above most dense conventional semiconductors in the visible range and is comparable to soft lattice solids. The authors further seek to understand the origin of this unusually sensitive thermochromic behavior and find that it arises from strong electron-phonon interactions and anharmonic phonons that significantly broaden band edges and lower the Eg with increasing temperature. The identification of structural signatures resulting in sensitive thermochromism in 1D vdW crystals opens avenues in discovering low-dimensional solids with strong temperature-dependent optical responses across broad spectral windows, dimensionalities, and size regimes.

Synthesis and Photocatalytic Activity of High-Quality Lead(II) Sulfide Nanoparticles from Lead(II) Thiosemicarbazone Complexes as Single Source Precursors

We report the synthesis of lead(II) complexes of 2-(thiophen-2-ylmethylene) hydrazine-1-carbothioamide (1) and 2-(1-(thiophen-2-yl) ethylene) hydrazine-1-carbothioamide (2), which were used as single source precursors in hexadecylamine (HDA) and oleylamine (OLA) at 190, 230, and 270°C to synthesize lead(II) sulfide nanoparticles. Optical studies by UV–vis analysis showed a general blue shift in the absorption band edge of the PbS nanoparticles (NPs) with energy bandgaps determined by Tauc’s plots ranging from 2.15 to 3.11 eV. The development of NPs with a variety of morphologies that changed with temperature and precursor type was demonstrated by morphological characterization using scanning electron microscopy and transmission electron microscopy. Cubic, rod-shaped, and nearly spherical-shaped PbS were formed. Powder X-ray diffraction (p-XRD) structural studies revealed the face-centered cubic structure of PbS nanoparticles. The elements contained in the nanoparticles were identified by energy dispersive X-ray spectroscopy (EDX). These results suggest that the size, shape, and optical properties of the synthesized PbS NPs were affected by reaction temperature, capping group, and precursor type. Under UV irradiation, the photocatalytic activity of HDA-capped PbS nanoparticles on the degradation of methylene blue dye ranged from 28.3% to 60.0%, with lead sulfide nanoparticle obtained by thermolysis of complex (1) at 230°C showing the highest photocatalytic efficiency (60.0%).