Mild Solution Method Research Articles

A Mild Synthesis of 0D Mn2+‐Doped Cs3CdBr5 Metal Halide for White Light‐Emitting Diodes and X‐Ray Imaging

AbstractAll‐inorganic Cd‐based metal halide is widely studied and applied in the field of optoelectronics due to its superior stability, diverse phase structure, and unique photoelectric properties. However, all‐inorganic 0D Cd‐based metal halide is not widely studied due to their extreme synthesis conditions. In this paper, a simple mild solution method is devised to successfully synthesize 0D Cs3CdBr5 by manipulating the crystal growth kinetics. Simultaneously, the influence of the doping element Mn on the transition matrix and the optical properties are investigated. By doping with an appropriate concentration of Mn2+, a green emission (520 nm) with photoluminescence quantum yield (PLQY) as high as 97.39% is obtained. Benefiting from near‐unity PLQY and the excellent optical properties, the white emitting light‐emitting diodes (WLEDs) with Cs3CdBr5:20%Mn as green phosphor exhibit warm white light emission with color rendering index (CRI) of 91 and correlated color temperature (CCT) of 4108 K. In addition, Cs3CdBr5:20%Mn also demonstrates excellent X‐ray scintillation properties with a low detection limit of 32.83 nGyair·s−1. The results show that Cs3CdBr5:Mn is not only a promising candidate for solid‐state lighting but also a promising candidate for low‐dose high‐resolution X‐ray imaging.

Mn4+-doped organometallic hafnium hexafluoride phosphors: Achieving near-unity quantum yield to elevate LED performance

Mn4+-activated fluoride phosphors with high luminous efficacy and short decay lifetimes are essential in realizing high-quality warm white-light-emitting diode (WLED) lighting. In this work, Mn4+-activated narrow-band red (∼630 nm) phosphor [(CH3)4N]2HfF6 was successfully synthesized by introducing an organic cationic group (tetramethylammonium) into the [HfF6]2- system using a mild chemical co-precipitation method. The sample structure was confirmed using various characterization techniques such as scanning electron microscopy, X-ray diffraction and Raman spectroscopy. Powder particles with diameters ranging from 10 to 20 um and double pyramidal structures were prepared by adjusting the anti-solvent temperature to control the crystal growth rate. The investigation of the morphology, structure and photoluminescence properties of Mn4+-doped [(CH3)4N]2HfF6 phosphors at different anti-solvent temperatures deepened our understanding of the correlation between structure and luminescence. Ultimately, phosphors with optimal performance (external quantum efficiency, ∼92.2%, and decay lifetime, ∼3.6 ms) were obtained. The samples were mixed with polydimethylsiloxane organosilicon to prepare a red light-conversion flexible film, and the (TMA)2HfF6:Mn4+ red phosphor and commercially available YAG:Ce3+ yellow-green phosphor was thoroughly mixed with transparent silica to form a stable paste, and then coated on a blue LED bead to prepare warm white LEDs, which significantly optimized the performance of the white LEDs (correlated color temperature, ∼5564 K). These experimental results indicate that the materials prepared by the mild solution method have important applications in the domains of display and lighting.

Explorations of Second-Order Nonlinear Optical Materials in the Monovalent Trithiocyanurate System

Two π-conjugated trithiocyanurates A(H2C3N3S3) (A = NH4, Cs) were successfully synthesized via a mild aqueous solution method or hydrothermal technique, and the ammonium bicarbonate and cesium hydroxide were used as deprotonation agents. NH4(H2C3N3S3) crystallizes in a symmetric space group P1̅ with flat [H2C3N3S3]∞ chain separated by NH4+, whereas Cs(H2C3N3S3) belongs to an asymmetric space group Cc [Z = 4, a = 5.405(6) Å, b = 21.263(3) Å, c = 14.996(2) Å, β = 92.408(10)°] with wavy [H2C3N3S3]∞ chain separated by Cs+. More importantly, Cs(H2C3N3S3) displays a strong second-harmonic generation effect (4.6 × KH2PO4), a large birefringence (Δn = 0.196@1064 nm), and a thermal stability up to 271.3 °C. In addition, a theoretical study further reveals that the π-conjugated (H2C3N3S3)− group has made a primary contribution toward enhancing the linear and nonlinear optical properties in the above two compounds.

Improved Energy Transfer in Mn-Doped Cs3Cu2I5 Microcrystals Induced by Localized Lattice Distortion.

With nontoxicity and high emission efficiency, luminescent copper(I)-based halides have attracted much attention as alternatives for lead-based perovskites in photoelectric domains. However, extending the emission wavelength by doping with Mn2+ in a facile way is still a challenge. In this work, Mn2+-doped Cs3Cu2I5 microcrystals were synthesized by a mild solution method, and double emission bands from self-trapped excitons (STEs) and Mn2+ peaking at 445 and 560 nm, respectively, were observed. More importantly, further introduction of alkali metal ions (Rb+, K+, Na+) considerably promoted the luminescence performance of the Cs3Cu2I5-Mn microcrystals. The STE → Mn2+ energy transfer efficiency of the typical sample doped with Na+ increased from ∼0 to 21.30%, and the photoluminescence quantum yield (PLQY) increased from 47.32% to 62.06%. The detailed structural and optical characterizations combined with DFT calculations proved that the doping with alkali metal ions causes lattice distortion and enhances the coupling between [MnI4] and [CuI4] tetrahedra, thus promoting the energy transfer efficiency and the PLQY.

Facile design of alloy-based hybrid layer to stabilize lithium metal anode

Lithium (Li) metal has been considered a promising anode candidate for next-generation energy-storage applications due to its ultrahigh capacity. However, the uncontrolled dendrite growth and continuous side reactions challenge the cycle life and practical application. Herein, by a facile and mild solution method, we build a compact LiZn alloy-based hybrid layer on the Li-metal surface. This hybrid layer exhibits favorable chemical stability, excellent wettability to electrolyte, and enhanced thermodynamic affinity to Li. As a result, the hybrid layer modified lihtium metal anode (HL-Li) enables accelerated Li-ion diffusion kinetics and dense Li deposition. Through the operando cell evaluation, moreover, we demonstrate that the hybrid layer restricts the Li dendrite growth of Li metal anodes effectively by reducing the volume expansion to half. Endowed with both thermodynamic and kinetic superiority, HL-Li exhibits low overpotential and prolonged cycles in both symmetric cells and full cells. Our work confirms the lithiophilic hybrid layer obtained by a facile solution process to enable dendrite-free deposition, providing a guidance for the synthesis of high-performance Li metal anode materials.

Excellent rate capability supercapacitor electrodes with highly hydroxyl ion adsorption capacity enabled by P-doped MnCo2O4 nanotube arrays

Doping or substitution of non-metallic ions is considered to be an effective way to improve the rate capability and cyclic stability of metal oxide electrodes. Nevertheless, current research lacks in-depth studies on the effect of doping on the rate capability. Herein, P-doped MnCo2O4 nanotubes with vertical array structure are rationally synthesized on carbon fibers via mild solution method and chemical heat treatment strategy. The density functional theory calculation and impedance test indicate that the introduced P atoms in MnCo2O4 are conducive to boost the conductivity and surface reactivity, as well as reaction kinetics. The electrochemicalmeasurementshowthat the novel P-doped MnCo2O4 nanotube electrodes deliver a highest specific capacitance of 996.7 F g−1. It also exhibits excellent rate performance of 81.7% original capacitance retention when the current density is increased by 30 times. An asymmetric supercapacitor P-doped MnCo2O4//activated carbon can realize a high energy density of 42.7 Wh kg−1at 750 W kg−1. Moreover, the device also exhibits a comparable cyclic retention of 81.9% at the end of the 8000th cycle. This work not only offers a potential electrode for energy storage but also provides a strategy for the preparation of hollow nanotubes structure with high electrochemical activities.

Field emission enhancement of composite structure of ZnO quantum dots and CuO nanowires by Al2O3 transition layer optimization

In this paper, ZnO quantum dots (QDs)-CuO nanowires (NWs) heterostructure was synthesized by a mild solution method. The Al2O3 transition layer were deposited on CuO NWs by surface modification engineering using atomic layer deposition (ALD) to increase the nucleation probability of ZnO QDs. The field emission properties of the composites were investigated. The results reveal that the CuO@Al2O3/ZnO QDs ternary heterostructures have the turn-on field of 2.82 V/μm and the field emission enhancement factor of 5798, which are superior to that of ZnO QDs-CuO NWs and pure CuO NWs. The improvement of field emission performance is mainly attributed to the decrease of the electron transport barrier at the interface and the increase of the oxygen vacancies, making it easier to transport electrons to ZnO QDs. The use of amorphous Al2O3 in the transition layer also effectively alleviates the lattice mismatch between ZnO QDs and the substrate. This study provides an effective method for enhancing the field emission performance of the core-shell nanomaterial device.

From Lead Iodide to a Radical Form Lead‐Iodide Superlattice: High Conductance Gain and Broader Band for Photoconductive Response

Superlattice materials offer new opportunities to modify optical and electrical properties of recently emerging 2D materials. The insertion of tetraethylbenzidine (EtDAB) into interlamination of the established 2D PbI2 semiconductor through a mild solution method yielded the first lead iodide superlattice, EtDAB⋅4PbI2 (EtDAB=tetraethylbenzidine), with radical and non-radical forms. The non-radical form has a non-ionic structure that differs from the common ionic structures for inorganic-organic hybrid lead halides. The radical form shows five orders of magnitude greater conductance and broader photoconductive response range (UV/Vis → UV/Vis-IR), than pure PbI2 and the non-radical form of the superlattice.

From Lead Iodide to a Radical Form Lead‐Iodide Superlattice: High Conductance Gain and Broader Band for Photoconductive Response

AbstractSuperlattice materials offer new opportunities to modify optical and electrical properties of recently emerging 2D materials. The insertion of tetraethylbenzidine (EtDAB) into interlamination of the established 2D PbI2 semiconductor through a mild solution method yielded the first lead iodide superlattice, EtDAB⋅4PbI2 (EtDAB=tetraethylbenzidine), with radical and non‐radical forms. The non‐radical form has a non‐ionic structure that differs from the common ionic structures for inorganic–organic hybrid lead halides. The radical form shows five orders of magnitude greater conductance and broader photoconductive response range (UV/Vis → UV/Vis‐IR), than pure PbI2 and the non‐radical form of the superlattice.

Temperature-induced fabrication of 1D mesoporous Co3O4 for high performance Li-ion batteries

In present work, 1D cobalt(II) complexes were fabricated by a novel temperature-induced approach. The morphology of the cobalt(II) complex can convert from 3D microsphere to 1D nanowire via controlling the reaction temperature (≥90 °C) without any surfactant with a mild chemical solution method. By calcining the 1D Cobalt complex, the mesoporous Co3O4 nanowires can be obtained. The 1D mesoporous Co3O4 exhibits superior reversible capacity of 933 mA h g−1 remained after 200 cycles at a high current density of 1.0 A g−1.

Transparent ternary alloy counter electrodes for high-efficiency bifacial dye-sensitized solar cells

Bifacial dye-sensitized solar cells (DSSCs) are regarded as promising photovoltaics to harvest solar energy from both front and rear sides because of their significantly increased total power outputs. Transparent counter electrodes (CEs) with cost-effectiveness and high electrocatalytic activity are crucial to make these high-performance bifacial devices. Herein, a category of transparent CEs from ternary alloys [(CoM)0.85Se, M = Ni, Ru, Fe] are synthesized by a mild solution method. Upon careful optimization on optical behaviors, electrocatalytic activity and photovoltaic performances, the bifacial DSSCs with (CoNi)0.85Se, (CoRu)0.85Se, (CoFe)0.85Se CEs achieve front power conversion efficiencies of 9.14%, 8.09%, 7.58% and rear efficiencies of 3.86%, 3.31%, 3.51% in comparison with 6.72% and 3.16% for state-of-the-art Pt CE based solar cell, respectively. Moreover, these bifacial DSSCs devices display high multiple on/off capability and relatively good stability.

Enhanced gas sensing characteristics of the flower-like ZnFe2O4/ZnO microstructures

ZnFe2O4/ZnO composites built from plenty of ZnFe2O4 nanoparticles decorated on the surfaces of ZnO microflowers were successfully prepared by a simple mild solution method combined with a subsequent calcination process. The morphologies and microstructures of the as-prepared samples were characterized by various techniques. In addition, a comparative sensing performance investigation between the two kinds of sensing materials manifested that the sensing properties of ZnFe2O4/ZnO microflowers were obviously enhanced compared with those of single ZnO microflowers component. For instance, the response of ZnFe2O4/ZnO microflowers to 50ppm acetone was ∼8.3 at 250°C, which was nearly 5.4-fold higher than that of primary ZnO microflowers at the same conditions. The synergetic effect and the formation of the heterojunction between ZnO and ZnFe2O4 along with the well-dispersed structures were believed to be the sources of the improvement of gas sensing properties.

Efficient electron transfer kuramite Cu3SnS4 nanosheet thin film towards platinum-free cathode in dye-sensitized solar cells

The density-functional theory calculations in this work clearly revealed that the kuramite-structure Cu3SnS4 material possessing the metallic characteristic, result in the higher charge transfer between I3− ions and the Cu3SnS4 surfaces, and the rapid redox transfer reaction of I3−/I− in dye-sensitized solar cells system. Then, a feasible and mild solution method was proposed to in-situ synthesize Cu-rich kuramite-structure Cu3SnS4 thin film on FTO substrate, and the acquired thin film was used directly as counter electrode to assemble dye-sensitized solar cells without any post-treatments. The obtained-Cu3SnS4 nanosheet film had good bonding strength, expanded surface area, low photoelectron charge transfer resistance at the counter electrode/electrolyte interface, and great catalytic activity toward the reduction of I3−/I− ions. Power conversion efficiency of 7.80% was obtained by utilizing Cu3SnS4 nanosheet as counter electrode, which was superior to that of Pt electrode (6.52%). Our results demonstrate the earth-abundant and low-cost kuramite Cu3SnS4 is an alternative Pt-free counter electrode material in dye-sensitized solar cells.

Highly transparent metal selenide counter electrodes for bifacial dye-sensitized solar cells

Creation of transparent counter electrode (CE) electrocatalysts for bifacial dye-sensitized solar cells (DSSCs) is a persistent objective for reducing cost of photovoltaic conversion. We present here the experimental realization of highly transparent CuSe CEs by a mild solution method for liquid-junction bifacial DSSCs. The resultant CuSe CEs show superior electrocatalytic activity toward I3− reduction reaction. By optimizing the pH values in synthesizing CuSe electrodes, the maximal front efficiency of 6.21% and rear efficiency of 4.72% are recorded on the corresponding bifacial DSSC. Both catalytic activity and photovoltaic performances can be further elevated by alloying CuSe with Co or Fe, yielding promising efficiencies of 7.81% and 5.38% under front and rear irradiations, respectively.

Dendritic Ag@Cu bimetallic interface for enhanced electrochemical responses on glucose and hydrogen peroxide

Dendritic Ag@Cu core–shell bimetallic nano-composite in low-cost was prepared at room temperature by a mild single-step solution method, and was further investigated by various characterization methods like Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM) and Atomic Force Microscope (AFM). The biosensors using dendritic Ag@Cu and ionic liquid (IL) as an electrochemical interface immobilizing glucose oxidase (GOx)/hemoglobin (Hb) were subsequently constructed for rapid detection of glucose/hydrogen peroxide (H2O2). The measurement results showed that the Ag@Cu significantly enhanced the electrochemical responses of GOx/Hb which remained their good bioactivity and high catalytic activity for glucose and H2O2. The developed biosensor has linear range of glucose concentration from 5 to 3000μM with a detection limit of 3μM and a linear range of H2O2 concentration from 0.5 to 50μM with a detection limit of 0.3μM (S/N=3), respectively. Especially for H2O2, catalytic effect of the biosensor was better, whose detection limit was reduced by an order of magnitude. The enhanced performance of the biosensors can be attributed to the unique structure of dendritic Ag@Cu core–shell, whose Cu shell can immobilize GOx/Hb via dendritic spines as well as retain its bioactivity, while the synergetic effect of Cu shell, Ag cores and IL can facilitate the transfer of electron between GOx/Hb and electrode, prevent from the denaturation and leakage of GOx/Hb.

Counter electrode electrocatalysts from binary Pd–Co alloy nanoparticles for dye-sensitized solar cells

A class of alloyed Pd–Co catalysts are prepared by a mild solution method and subsequently blended with poly(vinylidene fluoride) (PVDF) binder for coating cost-effective counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). The electrocatalytic activity for the I−/I3− redox electrolyte as well as photovoltaic performances of DSSCs are optimized by adjusting stoichiometric Pd/Co ratios. Due to the merits of resultant Pd–Co alloy CEs on good electrical conduction, rapid charge-transfer ability, and increased electrocatalytic activity, a maximum conversion efficiency of 6.44% is determined on the optimized DSSCs in comparable to 6.18% for Pt CE based DSSC. It is obvious that Pd–Co alloy CEs can be a better cost-effective and efficient alternative due to the expensive price and scarcity of Pt for the large scale applications of DSSCs.

Surface Ti3+/ Ti4+ Redox Shuttle Enhancing Photocatalytic H2 Production in Ultrathin TiO2 Nanosheets/CdSe Quantum Dots

Constructing unique nanocomposites to facilitate charge transfer and promote catalytic activity provides a promising approach for enhancing solar-to-hydrogen efficiency. However, revealing the catalytic surface state and understanding their roles in the photocatalytic process remain elusive. Here, we develop a facile and mild solution method for ultrathin TiO2 nanosheets with a large specific surface area and enhanced surface Ti3+ accumulation. Moreover, we demonstrate a hybrid nanosystem composed of ultrathin 2D TiO2 nanosheets directly coupled with 0D CdSe QDs for hydrogen generation. The 0D CdSe QDs increase visible light absorption ability after being coupled with the TiO2 nanosheets. Owing to the synergistic effect between the quantum dots and nanosheets, the apparent quantum efficiency increases to 45% at 380 and 450 nm, and the H2 evolution exhibits a 10-fold enhancement. EPR results indicate that the surface Ti3+ greatly promotes H free radical production due to the redox couple Ti3+/Ti4+ providin...

Structural and Spectral Characterization of Co2+- and Ni2+-DOPED CdO Powder Prepared From Solution at Room Temperature

The mild and simple solution method was used for the synthesis of Co2+- and Ni2+-doped CdO powders at room temperature. The prepared powders were characterized using powder X-ray diffraction, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), optical absorption, and Fourier transform infrared spectroscopy (FTIR). From the powder X-ray diffraction patterns, it has been observed that the prepared Co2+ and Ni2+ ion-doped CdO powders belong to the cubic phase, and the evaluated average crystalline sizes of the powders are 20 and 14 nm, respectively. The SEM images and the EDS spectra show that the prepared powders are distributed over different sizes in the grain boundaries. Optical absorption studies allow determination of site symmetry of the metal ion with its ligands. The crystal field (Dq) and inter-electronic repulsion (B and C) parameters have been evaluated from the optical absorption spectra. The FTIR spectra show the characteristic fundamental vibrations of the metal oxide and CdO.

Room temperature synthesis and spectral characterization of Cu2+-doped CdO powder

In the present study, we have synthesized undoped and Cu2+-doped CdO nanopowders by a mild solution method at room temperature. Powder X-ray diffraction, optical absorption, electron paramagnetic resonance and Fourier transform infrared measurements are used to characterize prepared powders. The powder X-ray diffraction patterns reflect the cubic crystal structure for undoped and Cu2+-doped CdO powders. Surface morphology images and compositional features are studied by scanning electron microscopy and energy-dispersive X-ray techniques, respectively. The optical absorption spectra exhibit a single absorption band for Cu2+-doped sample, which is the characteristic absorption band of distorted octahedral site symmetry. By correlating the electron paramagnetic resonance and optical results for Cu2+-doped CdO nanopowder, bonding parameters are evaluated. These values indicate the partial covalency of in-plane σ (α2) and in-plane π bonding (\( \beta_{1}^{2} \)) between copper ions and their ligands. The FT-IR spectra indicate the fundamental vibrations of Cd–O.

Counter electrodes from Mo–Se nanosheet alloys for bifacial dye-sensitized solar cells

Pursuit of cost-effective counter electrodes (CEs) with no sacrifice of photovoltaic performances is a persistent objective for dye-sensitized solar cells (DSSCs). We launch here the experimental realization of molybdenum selenide (Mo–Se) binary nanosheet CEs by a mild solution method. Due to high optical transparency, the bifacial DSSCs from cost-effective Mo–Se alloy CEs can realize electricity generation from either front or rear side. Particularly, the resultant Mo–Se alloy CEs show superior catalytic activity and charge-transfer ability toward I−/I3− redox electrolyte. The maximum front and rear efficiencies of 8.05% and 5.92% are recorded under simulated air mass 1.5 global irradiation, respectively. The impressive efficiency along with fast start-up, multiple start capability, and simple preparation highlights the potential application of the cost-effective and transparent Mo–Se alloy CE in robust bifacial DSSCs.