ProgrammableLight-Driven Color Tuning of PerovskiteQuantum Dots

Developing a precise and reproducible bandgap tuning method that enables tailored design of materials is of crucial importance for optoelectronic devices. Towards this end, we report a sphere diameter engineering (SDE) technique to manipulate the bandgap of two-dimensional (2D) materials. A one-to-one correspondence with an ideal linear working curve is established between the bandgap of MoS2 and the sphere diameter in a continuous range as large as 360 meV. Fully uniform bandgap tuning of all the as-grown MoS2 crystals is realized due to the isotropic characteristic of the sphere. More intriguingly, both a decrease and an increase of the bandgap can be achieved by constructing a positive or negative curvature. By fusing individual spheres in the melted state, post-synthesis bandgap adjustment of the supported 2D materials can be realized. This SDE technique, showing good precision, uniformity and reproducibility with high efficiency, may further accelerate the potential applications of 2D materials.

英文延伸摘要 SUMMARY In this study, phase formation and optical properties of (Sb1-xSnx)2Se3 (x = 0.0, 0.1, 0.2, 0.3) and Cu2FeSnSe4 (CFTSe) nanocrystals synthesized by various solvothermal processes were explored respectively. On synthesis at 190˚C in teflon-lined stainless steel autoclave, pure Sb2Se3 nanorods formed for 12 h, while pure (Sb1-xSnx)2Se3 nanorods formed for a longer time, 24-36 h, indicating that the Sn dopant increased the activation energy of Sb2Se3. The substitution solubility of Sn in Sb2Se3 was about 6 at%. The Sb2Se3 and (Sb1-xSnx)2Se3 nanorods were 50-150 nm in width and several μm in length. The growth direction of Sb2Se3 and (Sb1-xSnx)2Se3 nanorods was [001]. The bandgaps of (Sb1-xSnx)2Se3 (x = 0.0, 0.1, 0.2, 0.3) were 1.17, 1.21, 1.25, and 1.27 eV, respectively, which increased with the Sn concentration (x). The Sn-doped Sb2Se3 with tunable bandgap may be a promising candidate for photovoltaic applications. Pure and stoichiometric CFTSe nanocrystals were readily acquired for the Cu2Fe1.2Sn0.8Se4 samples using Fe(CH3COO)2 as the Fe source subjected to synthesis in oleylamine at 270˚C for 96 h. Two sharp Raman peaks at 170 and 186 cm-1 for CFTSe nanocrystals were identified. The higher reactivity of the Fe(CH3COO)2 precursor relative to the FeCl2 one enhanced the growth of pure CFTSe nanocrystals, while more Fe concentration in the Cu2FexSn0.8Se4 (x ≧ 1.3) samples led to the formation of CuFeSe2. The direct bandgap of CFTSe nanocrystals is about 1.16 eV. Key word：(Sb1-xSnx)2Se3、Cu2FeSnSe4 nanocrystals、one-pot system、wet chemical synthesis、 autoclave INTRODUCTION Recently, thin-films solar cells like copper indium gallium selenide (CIGS), and cadmium telluride (CdTe) have made impress improvements in device efficiency. However, due to the scarcity of Ga and In, and toxicity of Cd, both of CIGS and CdTe solar cells can’t popularize. Therefore, erth-abundant, non-toxic and low-cost materials should be explored for high-efficiency solar cells. V-VI compounds such as Sb2Se3, and Sb2S3, and the Cu2-II-IV-VI4 quaternary chalcopyrite compounds such as Cu2ZnSnS4 (CZTS), and Cu2ZnSnSe4 (CZTSe) containing non-toxic, abundant elements, and excellent opitical properties have drawn great attention as potential candidates for CIGS for use as the solar cell absorber layer. In order to opitimize the device conversion efficiency, the band gap of an ideal PV absorber layer should be around 1.3 eV for the single-junction cell and 1.0-1.9 eV for the two-junction cell. These requirements can be achieved by tunning the bandgaps of PV materials via adjusting the chemical compositions. Because few studies about the tunable bandgaps of Sb2Se3 and CFTSe were reported. In the present study, the tunable bandgap of Sn-doped Sb2Se3 nanocrystals and Cu2FeSnSe4 alloys were synthesised by one-pot system. MATERIALS AND METHODS For Sn-doped Sb2Se3 nanocrystals, a mixture of SnCl2∙2H2O, SbCl3 was dissolved in deionized water with magnetic stirring, and Se powders was dissolved in hydrazine. The resultant solution was transferred into a Teflon-lined stainless steel autoclave and maintained at 180-190℃ for 24-48 h. For Cu2FeSnSe4 alloys, a mixture of CuCl, Fe(CH3COO)2, SnCl4∙5H2O and Se powders was dissolved in OLA with magnetic stirring, and then heated at 270˚C in N2. The products was centrifuged and then washed with hexane and ethanol to remove the dissoluble by-product, and finally dried at about 50℃. The microstructure of samples was observed using scanning electron microscopy (SEM), and transmission electron microscopy (TEM).The chemical compositions of samples were measured with energy dispersive spectroscopy (EDS). The phases in the samples were analyzed using a X-ray diffractometer (XRD) and Raman spectra. The optical properties of samples were characterized using diffuse reflectance UV-vis spectroscopy in the range of 400-2000 nm. The valence states of the chemical elements in the samples were measured using X-ray photoelectron spectroscopy (XPS). RESULTS AND DISCUSSION Sb2Se3 and (Sb1-xSnx)2Se3 (x = 0.1, 0.2, 0.3) powders with single orthorhombic Sb2Se3 phase (JCPD 00-072-1184) were synthesized with autoclave at 190°C for 24-36 h. The XRD peaks of (Sb1-xSnx)2Se3 samples shift to lower diffraction angles as compared with that of the Sb2Se3 sample. From XPS measurement Sn and Sb in the (Sb1-xSnx)2Se3 samples are in the oxidation state of 2+ and 3+ respectively. The substitution of Sn for Sb in (Sb1-xSnx)2Se3 reduces its lattice constant because the ion radius of Sb3+, 0.076 nm, is smaller than that of Sn2+, 0.093 nm. The chemical compositions of (Sb1-xSnx)2Se3 samples show that the limit substitution soliblity of Sn in Sb2Se3 lattice is about 6 at%. The optical bandgap of Sb2Se3 and (Sb1-xSnx)2Se3 (x = 0.0, 0.1, 0.2, 0.3) nanocrystals are in the range of 1.17-1.27 eV, which are obtained from their reflectance spectra by performing the Kubelka-Munk transformation, showing that the optical bandgaps increase with the Sn concentrations. The Cu2FeSnSe4(CFTSe) samples were synthesized at 270˚C for 84-96 h to obtain pure CFTSe phase which was characterized by the sharp Raman peaks. The Raman spectrum of the sample with Fe(CH3COO)2 precursor synthesized at 270℃ for 96 h shows two sharp peak at 170 and 186 cm-1, both of which shift to lower frequencies as compared with the corresponding ones, 173 and 196 cm-1, of CZTSe. The variation in frequencies of two peaks is due to the change in the force constant of bond.From EDS/TEM analyses, the average chemical compositions of the CFTSe sample were Cu：Fe：Sn：Se = 25.1：13.0：12.4：49.5. CFTSe samples comprised nanoparticles, about 20-50nm in size, and nanosheets, about 50-100 nm in thickness and several hundred nm in size. When the sample with more concentration of Fe(CH3COO)2, Cu2FexSn0.8Se4(x ≧ 1.3), were synthesized at 270℃ for 72-120 h.The CuFeSe2(44-1305) along with the CFTSe phase was formed. The optical bandgap, 1.16 eV, of pure CFTSe was obtained from its reflectance spectra by performing the Kubelka-Munk transformation, which is close to the reported values. CONCLUSION 1. Sb2Se3 and (Sb1-xSnx)2Se3 (x = 0.1, 0.2, 0.3) powders with single orthorhombic Sb2Se3 phase (JCPD 00-072-1184) were synthesized with autoclave at 190°C for 24-36 h respectively. 2. The maximum substitution solubilities of Sn in Sb2Se3 were about 6 at%. 3. The bandgaps of (Sb1-xSnx)2Se3 (x = 0.0, 0.1, 0.2, 0.3) were 1.17, 1.21, 1.25, and 1.27 eV, respectively, which increased with the Sn concentration (x). 4. pure and stoichiometric CFTSe nanocrystals can be obtained when the Cu2Fe1.2Sn0.8Se4 samle using Fe(CH3COO)2 as Fe source is subjected to synthesis at 270℃ for 96 h in OLA 5. The Raman spectrum of the sample shows two sharp peak at 170 and 186 cm-1. 6. The direc bandgap of CFTSe nanocrystals is about 1.16 eV.

From synthesis to application, there are always certain interactions between the polar solvents and perovskite nanocrystals (NCs). To explain the effect of solvent polarity especially on the photoluminescence (PL) properties of NCs is highly desirable, especially for sensing applications. Herein We have synthesized the methylammonium lead mixed halides (MAPbCl3 - nBrn, where n = 0, 0.5, 1, 1.5) perovskite nanocrystals (NCs) at room temperature by using ligand-assisted re-precipitation (LARP) method, by employing mercaptoacetic acid (MAA) as a capping ligand. Different techniques have been employed to get information regarding the structural and optical properties of the synthesized material. Powder X-ray diffraction (PXRD) confirms the orthorhombic crystal structure of the MAPbCl3 - nBrn perovskite NCs. FT-IR (Fourier-transform infrared) analysis confirms the successful interaction of capping ligands with NCs. By increasing MABr precursor concentration during the synthesis of perovskite NCs, a red shift in the UV-Vis absorption and PL spectra has been observed. The steady-state photoluminescence (SSPL) and time-resolved photoluminescence (TRPL) techniques suggested that these perovskite NCs exhibit tunable PL relative to the substitution of Cl with Br in NCs. The comparative PL studies in non-polar (benzene) and polar (tetrahydrofuran (THF)) revealed that the PL properties are highly sensitive and selective toward the solvent chosen. All synthesized NCs possess longer PL lifetime in benzene than in THF. Relatively, perovskite NCs synthesized with 0.166 mM MABr precursor concentration show a longer PL lifetime (6.51 ns in benzene) as compared to other MABr concentrations. These studies not only propose that by controlling precursors concentration, one can synthesize NCs having tunable PL with a longer radiative PL lifetime, but also provide a comparative understanding of PL dynamics of NCs in different solvents.

Colloidal perovskite nanocrystals (NCs), especially the fully inorganic cesium lead halide (CsPbX3, X = Cl, Br, I) NCs, have been considered as promising candidates for lighting and display applications due to their narrow band emission, tunable band gap and high photoluminescence quantum yields (QYs). However, owing to the anion exchange in the CsPbX3 NCs, stable multi-color and white light emissions are difficult to achieve, thus limiting their practical optoelectronic applications. In this work, dual ion Bi3+/Mn2+ codoped CsPbCl3 perovskite NCs were prepared through the hot injection method for the first time to the best of our knowledge. Through simply adjusting the doping ion concentrations, the codoped NCs exhibited tunable emissions spanning the wide range of correlated color temperature (CCT) from 19 000 K to 4250 K under UV excitation. This interesting spectroscopic behaviour benefits from efficient energy transfer from the perovskite NC host to the intrinsic energy levels of Bi3+ or Mn2+ doping ions. Finally, taking advantage of the cooperation between the excitonic transition of the CsPbCl3 perovskite NC host and the intrinsic emissions from Bi3+ and Mn2+ ions, white light emission with the Commission Internationale de l'Eclairage (CIE) color coordinates of (0.33, 0.29) was developed in the codoped CsPbCl3 NCs.

Elimination of unexpected destruction on CsPbBrxI3-x nanocrystals arising from polymer matrix

Two-dimensional (2D) semiconductors for photocatalysis are more advantageous than the other photocatalytic materials since the 2D semiconductors generally have large specific surface area and abundant active sites. Phosphorus silicon (SiP), with an indirect bandgap in bulk and a direct bandgap in the monolayer, has recently emerged as an attractive 2D material because of its anisotropic layered structure, tunable bandgap, and high charge carrier mobility. However, the utilization of SiP as a photocatalyst for photocatalysis has been scarcely studied experimentally. Herein, we reported the synthesis of SiP nanosheets (SiP NSs) prepared from bulk SiP by an ultrasound-assisted liquid-phase exfoliation approach which can act as a metal-free, efficient, and visible-light-responsive photocatalyst for photocatalytic H2 production and nitrogen fixation. In a half-reaction system, the maximal H2 and NH3 generation rate under visible light irradiation achieves 528 and 35 μmol·h-1·g-1, respectively. Additionally, the apparent quantum yield for H2 production at 420 nm reaches 3.56%. Furthermore, a Z-scheme photocatalytic overall water-splitting system was successfully constructed by using Pt-loaded SiP NSs as the H2-evolving photocatalyst, Co3O4/BiVO4 as the O2-evolving photocatalyst, and Co(bpy)33+/2+ as an electron mediator. Notably, the highest H2 and O2 generation rate with respect to Pt/SiP NSs achieves 71 and 31 μmol·h-1·g-1, respectively. This study explores the potential application of 2D SiP as a metal-free visible-light-responsive photocatalyst for photocatalysis.

The increasing demands for high-speed imaging, aerospace, and optical communication have driven in-depth research on broadband photodetectors with high sensitivity and fast response. Two-dimensional (2D) materials have atomic-scale thickness, tunable bandgaps, and excellent carrier transport properties, making them ideal candidates for next-generation optoelectronics. However, their limited light absorption and intrinsic recombination losses remain key challenges. This paper provides an overview of recent progress of 2D-material-based broadband photodetectors. First, the fundamental optoelectronic properties of 2D materials, including bandgap modulation, carrier dynamics, and light–matter interactions, are discussed to clarify their broadband detection potential. Representative material systems, such as narrow-band gap semiconductors, 2D topological materials, and perovskites, are summarized, showing the detection ability from the ultraviolet to the mid-infrared regions. To overcome intrinsic limitations, four optimization strategies are highlighted: heterostructure engineering for efficient charge separation and extended spectral response; defect engineering to introduce mid-gap states and enhance sub-bandgap absorption; optical field enhancement through plasmonic nanostructures and optical cavities to improve responsivity; strain engineering for reversible band structure tuning, particularly suited for flexible devices. These strategies have achieved significant improvements in responsivity, detectivity, and bandwidth, with some devices implementing ultrabroadband detection and multifunctionality. In summary, 2D materials and their hybrids have shown great potential in broadband photodetection, with progress made in material innovation and device architecture optimization. The reviewed strategies, including heterostructure integration, defect modulation, optical field enhancement, and strain engineering, collectively demonstrate the different ways of overcoming intrinsic limitations and improving device performance. Looking ahead to the future, the reasonable combination of these methods is expected to further expand the detection window, improve sensitivity, and achieve multifunctional operations, thereby paving the way for the multifunctional applications of the next-generation broadband photodetectors in imaging, sensing, and optoelectronic systems.

Nanozymes are a class of nanomaterials with intrinsic biocatalytic activities. Compared to natural enzymes, they offer superior stability, precise structural tunability, and significant cost-effectiveness. Beyond serving as robust alternatives, nanozymes play increasingly pivotal roles in environmental monitoring, biosensing, and biomedical diagnostics. Despite significant strides, the rational orchestration of nanozyme activity remains elusive, primarily due to the intricate synergistic effects between atomic coordination environments, modulated electronic states, and interfacial microenvironments. In this review, we present a comprehensive and rational perspective on the multidimensional optimization of nanozyme catalytic performance. We first summarize the fundamental catalytic mechanisms and representative classes, emphasizing structure‒activity relationships at the nanoscale. Subsequently, strategies for enhancing performance are systematically discussed from two dimensions: intrinsic material regulation, including oxidation-state modulation and defect engineering, and extrinsic environmental regulation, such as pH and temperature. Furthermore, recent advances in theoretical calculations and machine learning-assisted approaches are critically reviewed, highlighting their emerging roles in guiding mechanism-informed and data-driven nanozyme design. By integrating mechanistic insights with intrinsic and extrinsic regulation strategies, this review aims to establish a unified framework for the rational optimization of nanozyme performance and provide guidance for future development.

Colloidal nanocrystals (NCs) play an important role inthe fieldof optoelectronic devices such as photovoltaic cells, photodetectors,and light-emitting diodes (LEDs). The properties of NC films are stronglyaffected by ligands attached to them, which constitute a barrier forcharge transport between adjacent NCs. Therefore, the method of surfacemodification by ligand exchange has been used to improve the electricalconductivity of NC films. However, surface modification to NCs inLEDs can also affect emission characteristics. Among NCs, nanorodshave unique properties, such as suppression of nonradiative Augerrecombination and linearly polarized light emission. In this work,CdSe/CdS nanorods (NRs) were prepared by the hot injection method.To increase the charge transport into CdSe/CdS NRs, we adopted ligandmodification to CdSe/CdS NRs. Using this technique, we could shortenthe injection barrier length between CdSe/CdS NRs and adjacent layers.It leads to a more balanced charge injection of electron/hole anda greatly increased current efficiency of CdSe/CdS NR-LEDs. In theNR-LEDs, the ligand exchange boosted the electroluminance, reachinga sixfold increase from 848 cd/m2 of native surfactantsto 5600 cd/m2 of the exchanged n-octanoicacid ligands at 12 V. The improvement of CdSe/CdS NR-LED performanceis closely correlated to the efficient control of charge balance vialigand modification strategy, which is expected to be indispensableto the future NR-LED-based optoelectronic system.

We investigate theoretically the effects of generation and injection of plasmonic carriers from an optically excited metal nanocrystal to a semiconductor contact or to surface molecules. The energy distributions of optically excited hot carriers are dramatically different in metal nanocrystals with large and small sizes. In large nanocrystals, the majority of hot carriers has very small excitation energies, and the excited-carrier distribution resembles the case of a plasmon wave in bulk. For nanocrystal sizes smaller than 20 nm, the carrier distribution extends to larger energies and occupies the whole region EF < ε < EF + ℏω. The physical reason for the above behaviors is nonconservation of momentum in a nanocrystal. Because of the above properties, nanocrystals of small sizes are most suitable for designing opto-electronic and photosynthetic devices based on injection of plasmonic electrons and holes. For gold nanocrystals, the optimal sizes for efficient generation of hot carriers with overbarrier energies are in the range of 10–20 nm. Another important factor is the polarization of the exciting light. For efficient excitation of carriers with high energies, the electric-field polarization vector should be perpendicular to a prism-like nanoantenna (slab or platelet). We also show the relation between our theory for injection from plasmonic nanocrystals and the Fowler theory of injection from a bulk metal. Along with a prism geometry (or platelet geometry), we consider cubes. The results can be applied to design both purely solid-state opto-electronic devices and systems for photocatalysis and solar-energy conversion.

Abstract

The versatile hybrid perovskite nanocrystals (NCs) are one of the most promising materials for optoelectronics by virtue of their tunable bandgaps and high photoluminescence (PL) quantum yields. However, their inherent crystalline chemical structure limits the chiroptical properties achievable with the material. The production of chiral perovskites has become an active field of research for its promising applications in optics, chemistry, or biology. Typically, chiral halide perovskites are obtained by the incorporation of different chiral moieties in the material. Unfortunately, these chemically modified perovskites have demonstrated moderate values of chiral PL so far. Here, a general and scalable approach is introduced to produce chiral PL from arbitrary nanoemitters assembled into 2D-chiral metasurfaces. The fabrication via nanoimprinting lithography employs elastomeric molds engraved with chiral motifs covering millimeter areas that are used to pattern two types of unmodified colloidal perovskite NC inks: green-emissive CsPbBr3 and red-emissive CsPbBr1 I2 . The perovskite 2D-metasurfaces exhibit remarkable PL dissymmetry factors (glum ) of 0.16 that can be further improved up to glum of 0.3 by adding a high-refractive-index coating on the metasurfaces. This scalable approach to produce chiral photoluminescent thin films paves the way for the seamless production of bright chiral light sources for upcoming optoelectronic applications.

Pure‐red CsPbBrxI3−x nanocrystals (NCs) light‐emitting diodes (PeLEDs) are promising candidates for high‐performance display due to their high brightness, excellent color purity and readily tunable band gap. However, achieving highly stable pure‐red PeLEDs is still challenging due to phase segregation in the mixed halide CsPbBrxI3−x NCs. Herein, pure‐red mixed halide CsPbBrxI3−x NCs with a relatively small size are synthesized using phosphate acid as a ligand, effectively avoiding spontaneous phase separation. The strong interaction between phosphate ligands and Pb2+ facilitates the slow formation of CsPbBrxI3−x NCs, resulting in relatively small NC sizes. In addition, a dense phosphate passivation layer forms around the surface of NCs, which imparts excellent stability to the NCs against light, moisture and heat treatment. Utilizing the highly stable CsPbBrxI3−x NCs as an emission layer, pure‐red PeLEDs emitting at 633 nm, with an external quantum efficiency (EQE) of 10.0%, a brightness of 8231 cd m−2 and a half‐life of 393 min, are fabricated. Notably, the PeLEDs show excellent stability, with negligible changes in the emission spectra under an elevated bias voltage of 14 V. This work provides a new avenue for enhancing the performance of pure red PeLEDs through strongly coordinated phosphate ligand passivation.

2D/2D NiAl LDH integrated graphitic carbon nitride with robust interfacial contact for driving photocatalytic hydrogen production

We report on the ferroelectric properties of single-phase wurtzite ScGaN grown on GaN by plasma-assisted molecular beam epitaxy. Distinct ferroelectric switching behavior was confirmed by detailed electrical characterization. Coercive fields in the range of 2.0–3.0 MV/cm and large, retainable remnant polarization in the range of 60–120 μC/cm2 are unambiguously demonstrated for ScGaN epilayers with Sc contents of 0.31–0.41. Taking advantage of the widely tunable energy bandgap of III-nitride semiconductors, the demonstration of ferroelectricity in ScGaN, together with the recently reported ferroelectric ScAlN, will enable a broad range of emerging applications with combined functionality in ferroelectric, electronic, optoelectronic, photovoltaic, and/or photonic devices and systems.