Tunable CO2-to-syngas conversion via strong electronic coupling in S-scheme ZnGa2O4/g-C3N4 photocatalysts.

The conversion of CO2 into syngas, a mixture of CO and H2, via photocatalytic reduction, is a promising approach towards achieving a sustainable carbon economy. However, the evolution of highly adjustable syngas, particularly without the use of sacrifice reagents or additional cocatalysts, remains a significant challenge. In this study, a step-scheme (S-scheme) 0D ZnGa2O4 nanodots (∼7 nm) rooted g-C3N4 nanosheets (denoted as ZnGa2O4/C3N4) heterojunction photocatalyst was synthesized vis a facial in-situ growth strategy for efficient CO2-to-syngas conversion. Both experimental and theoretical studies have demonstrated that the polymeric nature of g-C3N4 and highly distributed ZnGa2O4 nanodots synergistically contribute to a strong interaction between metal oxide and C3N4 support. Furthermore, the desirable S-scheme heterojunction in ZnGa2O4/C3N4 efficiently promotes charge separation, enabling strong photoredox ability. As a result, the S-scheme ZnGa2O4/C3N4 exhibited remarkable activity and selectivity in photochemical conversion of CO2 into syngas, with a syngas production rate of up to 103.3 µ mol g-1 h-1, even in the absence of sacrificial agents and cocatalyst. Impressively, the CO/H2 ratio of syngas can be tunable within a wide range from 1:4 to 2:1. This work exemplifies the effectiveness of a meticulously designed S-scheme heterojunction photocatalyst for CO2-to-syngas conversion with adjustable composition, thus paving the way for new possibilities in sustainable energy conversion and utilization.

Eu3+ Single-Doped Phosphor with Antithermal Quenching Behavior and Multicolor-Tunable Properties for Luminescence Thermometry.

To date, non-contact luminescence thermometry methods based on fluorescence intensity ratio (FIR) technology have been studied extensively. However, designing phosphors with high relative sensitivity (Sr) has become a research hotspot. In this work, Eu3+ single-doped Ca2Sb2O7:Eu3+ phosphors with a high Sr value for dual-emitting-center luminescence thermometry are developed and proposed. The anti-thermal quenching behavior of Eu3+ originating from the energy transfer (ET) of host → Eu3+ is found and proved in the designed phosphors. Interestingly, adjustable color emission from blue to orange can be achieved. Surprisingly, the degree of the anti-thermal quenching behavior of Eu3+ gradually reduces from 240 to 127% as the Eu3+ doping content increases from 0.005 to 0.05 mol, attributed to most Eu3+ being located in the low symmetrical [Ca1O8] dodecahedral site. According to the differentiable responses of the host and Eu3+ to temperature, the maximal Sr value reaches 3.369% K-1 (383 K). Moreover, the ambient temperature can be intuitively predicted by observing the emitting color. Owing to the excellent performance in optical thermometry, color-tunable properties, and outstanding acid and alkali resistance for polydimethylsiloxane (PDMS) films, the developed Eu3+ single-doped Ca2Sb2O7:Eu3+ phosphors are expected to be prospective candidates in luminescence thermometers and LED devices in various conditions.

Interfacial engineering of heterostructured Fe-Ni3S2/Ni(OH)2 nanosheets with tailored d-band center for enhanced oxygen evolution catalysis.

Hydrogen production by electrochemical water splitting suffers from high kinetic barriers in the anodic oxygen evolution reaction (OER), which limits the overall efficiency. Herein, we report a structural and electronic engineering strategy by integrating self-standing Fe-doped Ni3S2 (denoted by Fe-Ni3S2) nanosheet arrays with Ni(OH)2 subunits to form heterostructured Fe-Ni3S2/Ni(OH)2 on a Ni Foam substrate. The strong electronic interaction between the Fe-Ni3S2 and Ni(OH)2 constituents contributes abundant catalytic sites and ensures high electron transfer. Moreover, the combined experimental and theoretical study revealed that the coupling of Ni(OH)2 onto the Fe-Ni3S2 is favorable for lowering the activation energy of water oxidation for favorable OER kinetics and upshifting the Ni d-band center to facilitate the adsorption of O-containing intermediates. Consequently, the optimized Fe-Ni3S2/Ni(OH)2 hybrid catalyst exhibits excellent OER performance in alkaline electrolytes with an ultralow overpotential of 202 mV at 10 mA cm-2, a small Tafel slope of 50.6 mV dec-1, and long-term durability under high current density (0.25 A cm-2) for up to 60 h without significant deactivation. Moreover, a two-electrode Fe-Ni3S2/Ni(OH)2||Pt/C electrolyzer requires only a low voltage of 1.54 V at 10 mA cm-2 for overall water splitting. This study emphasizes the importance of interface and surface engineering in achieving highly efficient electrocatalysts.

Epitaxial Growth of Lead-Free 2D Cs3 Cu2 I5 Perovskites for High-Performance UV Photodetectors.

The all-inorganic lead-free Cu-based halide perovskites represented by the Cs-Cu-I system, have sparked extensive interest recently due to their impressive photophysical characteristics. However, successive works on their potential application in light emission diodes and photodetectors rely on tiny polycrystals, in which the grain boundaries and defects may lead to the performance degradation of their embodied devices. Here, 2D all-inorganic perovskite Cs3 Cu2 I5 single crystals are epitaxially grown on mica substrates, with a thickness down to 10 nm. The strong blue emission of the Cs3 Cu2 I5 flakes may originate from the radiative transition of self-trapped excitons associated with a large Stocks shift and long (microsecond) decay time. Ultravioelt (UV) photodetectors based on individual Cs3 Cu2 I5 nanosheets are fabricated via a swift and etching-free dry transfer approach, which reveal a high responsivity of 3.78 A W-1 (270 nm, 5 V bias), as well as a fast response speed (τrise  ≈163 ms, τdecay  ≈203 ms), outperforming congeneric UV sensors based on other 2D metal halide perovskites. This work therefore sheds light on the fabrication of green optoelectronic devices based on lead-free 2D perovskites, vital for the sustainable development of photoelectric technology.

Synergistic luminescent thermometer using co-doped Ca2GdSbO6:Mn4+/(Eu3+ or Sm3+) phosphors.

Luminescent thermometers provide a non-contact method of probing temperature with high sensitivity and response speed at the nanoscale. Synergistic photoluminescence from different activators can realize high sensitivity for luminescent thermometers by finely selecting ions with specific crystallographic sites. Herein, the more temperature-sensitive Mn4+ and the less-sensitive Eu3+ (or Sm3+) activators are co-doped into a Ca2GdSbO6 matrix to form an effective thermometer, where Mn4+ and Eu3+ (or Sm3+) ions occupy the Sb5+ and Gd3+ sites, respectively. The co-doping of Eu3+ ions or Sm3+ ions leads to lattice expansion of Ca2GdSbO6 matrix and a tuned narrow emission from deep-red to orangish-red. According to the ratio of luminescence intensity, the maximal Sa and Sr values are 0.19 K-0 (347 K) and 1.38% K-( (420 K) for Ca2GdSbO6:Mn4+/Eu3+ probe and 0.26 K-p (363 K) and 1.55% K-( (430 K) for Ca2GdSbO6:Mn4+/Sm3+ probe thermometers, respectively. In addition, thermometers based on Mn4+ emission lifetimes can provide the highest relative sensitivity of 1.47% K-s at 425 K. Thus, the highly-temperature-sensitive Ca2GdSbO6:Mn4+/(Eu3+ or Sm3+) phosphor is a promising candidate for practical luminescence thermometers.

In Situ Transformation of Metal-Organic Frameworks into Hollow Nickel-Cobalt Double Hydroxide Arrays for Efficient Water Oxidation.

Developing earth-abundant electrocatalysts for efficient oxygen evolution reaction (OER) is of paramount significance for electrochemical water splitting. Herein, an efficient in situ etching-deposition growth strategy is employed to transform pristine two-dimensional (2D) Co-metal-organic frameworks into hollow Ni/Co double hydroxide arrays (denoted as Ni/Co-DH), which not only yields a larger surface area and exposes more active sites but also decreases the activation energy to the OER. With structural and compositional benefits, the Ni/Co-DH exhibits high performance with an overpotential of 229 mV at 10 mA cm-2 and exceptional long-term stability of over 90 h in 1 M KOH medium for OER, comparable to most non-noble oxygen evolution catalysts reported so far. In addition, a two-electrode Ni/Co-DH∥Pt/C electrolyzer also requires a considerably low voltage of 1.58 V at 10 mA cm-2 for overall water splitting. This study affords a rational strategy to develop water-alkali electrolyzers with great complexity for large-scale water-splitting systems.

Local Structure Modulation-Induced Highly Efficient Red-Emitting Ba2Gd1-xYxNbO6:Mn4+ Phosphors for Warm WLEDs.

Modulating the crystal field environment around the emitting ions is an effective strategy to improve the luminescence performance of the practical effective phosphor materials. Here, smaller Y3+ ions are introduced into substituting the Gd3+ sites in Ba2GdNbO6:Mn4+ phosphor to modify the optical properties, including the enhanced luminescence intensity, redshift, and longer lifetime of the Mn4+ ions. The substitution of smaller Y3+ ions leads to lattice contraction and then strengthens pressure on the local structure, enhances lattice rigidity, and suppresses nonradiative transition. Moreover, the prototype phosphor-converted light-emitting diode (LED) demonstrates a continuous change photoelectric performance with a correlated color temperature of 4883-7876 K and a color rendering index of 64.1-83.2, suggesting that it can be one of the most prospective fluorescent materials applied as a warm red component for white LEDss. Thus, the smaller ion partial substitution can provide a concise approach to modulate the crystal field environment around the emitting ions for excellent luminescence properties of phosphors toward the modern artificial light.

Dual-phase glass ceramics for dual-modal optical thermometry through a spatial isolation strategy.

Glass ceramics (GCs) can be an ideal medium for dopant spatial isolation, avoiding the adverse energy transfer process. Herein, a spatial isolation strategy is proposed and fulfilled by dual-phase GCs. Structural characterization performed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED), verified the successful dual-phase precipitation of tetragonal LiYF4 and cubic ZnAl2O4 nanocrystals (NCs) among aluminosilicate glasses. Impressively, it is evidenced that intense blue upconversion (UC) emission of Tm3+ and deep red DS emission can be attained simultaneously upon 980 nm NIR and 400 nm violet light excitation, respectively, owing to the extremely suppressed adverse energy transfer process between physically separated Tm3+ and Cr3+. This also suggests the partition of Yb3+ and Tm3+ into LiYF4 and Cr3+ into ZnAl2O4 respectively. In particular, optical thermometry based on the fluorescence intensity ratio (FIR) of Tm3+ and fluorescence lifetime of Cr3+ of dual-phase GCs were also performed in detail, with the maximum relative sensitivity of 1.87% K-1 at 396 K and 0.81% K-1 at 503 K, respectively. As a consequence, such a spatial isolation strategy would provide a convenient route for application in optical thermometry and extend the practical application of GC materials.

Visible-light-responsive Z-scheme system for photocatalytic lignocellulose-to-H2 conversion.

A Z-scheme system was successfully constructed for visible-light-driven photocatalytic H2 production from lignocelluloses, the highest H2 evolution rate of this Z-scheme system is 5.3 and 1.6 µmol h-1 in α-cellulose and poplar wood chip aqueous solutions, respectively, under visible light irradiation.

Advances in Halide Perovskite Memristor from Lead-Based to Lead-Free Materials.

Memristors have attracted considerable attention as one of the four basic circuit elements besides resistors, capacitors, and inductors. Especially, the nonvolatile memory devices have become a promising candidate for the new-generation information storage, due to their excellent write, read, and erase rates, in addition to the low-energy consumption, multistate storage, and high scalability. Among them, halide perovskite (HP) memristors have great potential to achieve low-cost practical information storage and computing. However, the usual lead-based HP memristors face serious problems of high toxicity and low stability. To alleviate the above issues, great effort has been devoted to develop lead-free HP memristors. Here, we have summarized and discussed the advances in HP memristors from lead-based to lead-free materials including memristive properties, stability, neural network applications, and memristive mechanism. Finally, the challenges and prospects of lead-free HP memristors have been discussed.

LiYF4-nanocrystal-embedded glass ceramics for upconversion: glass crystallization, optical thermometry and spectral conversion.

Glass ceramics (GCs) can perfectly integrate nanocrystals (NCs) into bulk materials. Herein, GCs containing LiYF4 NCs were fabricated via a traditional melt-quenching method and subsequent glass crystallization. Structural characterization was carried out via X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and scanning transmission electron microscopy high-angle annular dark-field (STEM-HAADF) analysis, suggesting the precipitation of LiYF4 NCs from a glass matrix. Taking Eu3+ as a structural probe, the spectrographic features provide compelling evidence for the partition of dopants. In particular, intense upconversion (UC) emission was achieved when co-doped with Yb3+ and Er3+. Temperature-dependent UC emission behaviour was also established based on the fluorescence intensity ratio (FIR) of Er3+, to study its properties for optical thermometry. Furthermore, spectral conversion was attained through cross relaxation (CR) between Ce3+ and Ho3+, tuning from green to red with various Ce3+ doping concentrations. There is evidence that LiYF4 NC-embedded GCs were favorable for UC, which may be extremely promising for optical thermometry and spectral conversion applications. This work may open up new avenues for the exploration of GC materials for expansive applications.

Construction of hierarchical CoP@Ni2P core-shell nanoarrays for efficient electrocatalytic hydrogen evolution in alkaline solution.

Design and synthesis of non-noble electrocatalyst with controlled structure and composition for hydrogen evolution reaction (HER) are significant for large-scale water electrolysis. Here, an elegant multi-step templating strategy is developed for the fabrication of vertically aligned CoP@Ni2P nanowire-nanosheet architecture on Ni foam. Cobalt-carbonate hydroxides nanowires grown on Ni foam are first synthesized as the self-template. Afterward, a layer of amorphous Ni(OH)2 nanosheets is grown on the Co-based precursors through a chemical bath process, which is then transformed into the hierarchical CoP@Ni2P nanoarrays by a co-phosphatization treatment. Owing to the synergistic effect of the compositions and the advantages of the hierarchical heterostructures, the resulting hybrid electrocatalyst with dense heterointerfaces is revealed as an excellent HER catalyst, with a low overpotential of 101 mV at the current density of 10 mA cm-2, a relatively small Tafel slope of 79 mV dec-1, and favorable long-term stability of at least 20 h in 1 M KOH.

Promoting photoluminescence quantum yields of glass-stabilized CsPbX3 (X = Cl, Br, I) perovskite quantum dots through fluorine doping.

In the last few years, all-inorganic cesium lead halide (CsPbX3) quantum dots have shown unprecedented radical progress for practical applications in the optoelectronic field, but they quickly decompose when exposed to air. The in situ growth of the CsPbX3 particles inside amorphous glass can significantly improve their stability. Unfortunately, it is formidably difficult to precipitate whole-family CsPbX3 from a glass matrix and their photoluminescence quantum yields require further improvement. Herein, fluoride additives were introduced into oxyhalide borosilicate glasses to break the tight glass network, which promoted the nucleation/growth of CsPbX3 (X = Cl, Cl/Br, Br, Br/I and I) inside the glass. Importantly, the quantum efficiencies of glass-stabilized CsPbBr3, CsPb(Br/I)3 and CsPbI3 reached 80%, 60% and 50%, respectively, which are the highest efficiencies reported so far. Benefiting from the effective protection of robust glass, CsPbX3 quantum dots exhibited superior water resistance with more than 90% luminescence remaining after immersing them in water for 30 days, and halogen anion exchange among different CsPbX3 materials was completely inhibited. Two prototype light-emitting diodes were constructed by coupling green/red and green/orange/red quantum dots with InGaN blue chips, yielding bright white light with optimal luminous efficiency of 93 lm W-1, tunable color temperature of 2000-5800 K and high color rendering index of 90.

Schottky junction effect enhanced plasmonic photocatalysis by TaON@Ni NP heterostructures.

We chemically deposited amorphous Ni(OH)2 layers over TaON particles with irregular surface morphology, and subsequently in situ reduced them to Ni (10-20 nm) nanoparticles, to construct a TaON@Ni photocatalyst. Such a hierarchical hybrid aims to combine the enhanced light absorption by the metal Ni plasmonic effect with accelerated charge separation by a Schottky barrier, and herein, achieves a higher photocatalytic activity in CO2 reduction than TaON.

Ta3N5 nanorods encapsulated into 3D hydrangea-like MoS2 for enhanced photocatalytic hydrogen evolution under visible light irradiation.

Tantalum nitride (Ta3N5) with an appealing band gap (∼2.1 eV) has emerged as a promising catalyst in the photocatalysis field. However, Ta3N5 application in the photocatalytic hydrogen evolution reaction (HER) is limited due to disadvantages such as unsatisfactory separation and transfer of photogenerated carriers. Here we utilize MoS2 as co-catalysts to promote the kinetics of photocatalytic H2 evolution over Ta3N5. The Ta3N5 nanorods were encapsulated into 3D hydrangea-like MoS2 for maximizing the contact areas between Ta3N5 and MoS2 and offering rich active sites. More importantly, spectroscopic analysis and theoretical calculations consistently reveal that the unique interfacial interaction, as well as the matching band alignment between Ta3N5 and MoS2, accelerates the photogenerated charge extraction from Ta3N5 to MoS2, reducing charge recombination losses in Ta3N5. Thus, the optimized Ta3N5/MoS2 hybrid exhibits a substantially enhanced hydrogen evolution rate (56.5 µmol h-1), over 22 times higher than that of pristine Ta3N5. This work may provide a general strategy to overcome the low photocatalytic activity of nitrides for hydrogen evolution.

Encapsulating MnSe Nanoparticles Inside 3D Hierarchical Carbon Frameworks with Lithium Storage Boosted by in Situ Electrochemical Phase Transformation.

Electrode materials that act through the electrochemical conversion mechanism, such as metal selenides, have been considered as promising anode candidates for lithium-ion batteries (LIBs), although their fast capacity attenuation and inadequate electrical conductivity are impeding their practical application. In this work, these issues are addressed through the efficient fabrication of MnSe nanoparticles inside porous carbon hierarchical architectures for evaluation as anode materials for LIBs. Density functional theory simulations indicate that there is a completely irreversible phase transformation during the initial cycle, and the high structural reversibility of ß-MnSe provides a low energy barrier for the diffusion of lithium ions. Electron localization function calculations demonstrate that the phase transformation leads to high charge transfer kinetics and a favorable lithium ion diffusion coefficient. Benefitting from the phase transformation and unique structural engineering, the MnSe/C chestnut-like structures with boosted conductivity deliver enhanced lithium storage performance (885 mA h g-1 at a current density of 0.2 A g-1 after 200 cycles), superior cycling stability (a capacity of 880 mA h g-1 at 1 A g-1 after 1000 cycles), and outstanding rate performance (416 mA h g-1 at 2 A g-1).

Simultaneous Tailoring of Dual-Phase Fluoride Precipitation and Dopant Distribution in Glass to Control Upconverting Luminescence.

In situ glass crystallization is an effective strategy to integrate lanthanide-doped upconversion nanocrystals into amorphous glass, leading to new hybrid materials and offering an unexploited way to study light-particle interactions. However, the precipitation of Sc3+-based nanocrystals from glass is rarely reported and the incorporation of lanthanide activators into the Sc3+-based crystalline lattice is formidably difficult owing to their large radius mismatch. Herein, it is demonstrated that lanthanide dopants with smaller ionic radii can act as nucleating agents to promote the nucleation/growth of KSc2F7 nanocrystals in oxyfluoride aluminosilicate glass. A series of structural and spectroscopic characterizations indicate that Ln-dopant-induced K/Sc/Ln/F amorphous phase separation from glass is an essential prerequisite for the precipitation of KSc2F7 and the partition of Ln dopants into the KSc2F7 lattice by substituting Sc3+ ions. Importantly, modifying the Ln-to-Sc ratio in glass enables to control competitive crystallization of KSc2F7 and Ln-based (KYb2F7, KLu2F7, and KYF4) nanocrystals and produce dual-phase fluoride-embedded nanocomposites with distinct crystal fields. Consequently, tunable multicolor upconversion luminescence can be achieved through diversified regulatory approaches, such as adjustment of the dual-phase ratio, selective separation of Ln3+ dopants, and alteration of incident pumping laser. As a proof-of-concept experiment, the application of dual-phase glass as a color converter in 980 nm laser-driven upconverting lighting is demonstrated.

Chlorine-additive-promoted incorporation of Mn2+ dopants into CsPbCl3 perovskite nanocrystals.

Effective Mn2+ doping in a CsPbCl3 lattice utilizing manganese acetate and trimethylchlorosilane is achieved via a one-pot hot-injection synthesis method. This strongly contrasts to the previous case, where only the MnCl2 precursor was suitable for Mn2+ doping by considering the matching of bond dissociation energies between Mn-Cl and Pb-Cl. The Mn doping concentration and luminescence quantum yield are highly dependent on trimethylchlorosilane content. A new doping mechanism is proposed, where the incorporation of Mn2+ into CsPbCl3 is achieved via directly inserting [MnCl6]4- octahedra into the perovskite structure during the nucleation/growth processes instead of Mn-to-Pb cation exchange. Accordingly, increasing Cl- content in the reaction solution indeed promotes the doping of other divalent transition metal ions such as Ni2+, Cu2+ and Zn2+ in CsPbCl3 and improve the quantum yield of CsPbCl3 nanocrystals up to ∼20% compared to the undoped counterparts (∼1%).

Grinding Synthesis of APbX3 (A = MA, FA, Cs; X = Cl, Br, I) Perovskite Nanocrystals.

Currently, metal halide perovskite nanocrystals have been extensively explored due to their unique optoelectronic properties and wide application prospects. In the present work, a facile grinding method is developed to prepare whole-family APbX3 (A = MA, FA, and Cs; X = Cl, Br, and I) perovskite nanocrystals. This strategy alleviates the harsh synthesis conditions of precursor dissolution, atmosphere protection, and high temperature. Impressively, the as-prepared perovskite nanocrystals are evidenced to have halogen-rich surfaces and yield visible full-spectral emissions with maximal photoluminescence quantum yield up to 92% and excellent stability. Additionally, the grinding method can be extended to synthesize widely concerned Mn2+-doped CsPbCl3 nanocrystals with dual-modal emissions of both excitons and dopants. As a proof-of-concept experiment, the present perovskite nanocrystals are demonstrated to be applicable as blue/green/red color converters in UV-excitable white-light-emitting diodes.

Optimizing and adjusting the photoluminescence of Mn4+-doped fluoride phosphors via forming composite particles.

Nowadays, Mn4+-doped red phosphors are widely used in white LEDs to improve the color rendering index and decrease the correlated color temperature. Great efforts have been made to enhance the luminous efficiency. In this work, new composite particles containing two fluorides with similar structures K2LiAlF6 and K2NaAlF6 were developed to improve the emission intensity. The composite particles contain K2LiAlF6 and K2NaAlF6 phases with an increase of Na content. The particle sizes of the products were in the nanoscale and the element distribution was investigated. Importantly, the as-prepared composite particles had higher emission intensity than simple mixtures. Structural and optical characterization studies were systematically carried out to understand the enhancement mechanism. Finally, a white LED device was fabricated by combining the synthesized red phosphor and YAG:Ce on a blue chip.