Wide Range Near-Zero Thermal Quenching of Orange-Yellow Phosphor via Impeding Self-Oxidation of Eu2+ for Versatile Optoelectronic Applications.

Li2SrSiO4:Eu2+ is a promising substitute for traditional Y3Al5O12:Ce3+ (YAG:Ce3+) owing to its strong orange-yellow emission of 4f-5d transition originating from Eu2+ dopant, covering the more red-light region. However, its inevitable luminescence thermal quenching at high temperatures and the self-oxidation of Eu2+ strongly impede their applications. Their remediation remains highly challenging. Herein, an anti-self-oxidation(ASO) concept of Eu2+ in Li2SrSiO4 substrate by adding trivalent rare-earth ions (A3+: A = La, Gd, Y, Lu) for highly efficient and stable orange-yellow light emission have been proposed. A significantly increased orange-yellow emission (202% improvement) from Li2Sr0.95A0.05SiO4:Eu2+ with a wide range near-zero thermal quenching is obtained, superior to other Eu2+ activated phosphors. The presence of A3+ ions with various radii modifies the ASO degree of Eu2+ ions, achieving the tunable chemical state, composition, electronic configuration, crystal-field strength, and luminescent characteristics of the developed phosphors. For the proof of the concept, a W-LED device and a PDMS (Polydimethylsiloxane) luminescent film are fabricated, endowing excellent luminescence performance and thermal stability and the huge application prospects of Li2SrSiO4:Eu2+ in lighting and display fields.

Degree of Crystal Structure Distortion-Induced Tunable LiGaO2 Long Persistent Luminescence for Optical Information Encryption.

Tunable long persistent luminescence (LPL) phosphor materials have great potential for optoelectronic cryptographic applications. However, the mainstream techniques of modulating LPL generally have the characteristics of complex preparation processes, demanding crystal field environments, or expensive dopant ions, which restrict large-scale commercial application. Herein, we develop a simple, high-efficiency, and low-cost strategy to optimize the LPL of LiGaO2(LGO):Cu2+ by changing the sintering time to regulate the degree of crystal structure distortion. The Cu2+ as charge compensation will substantially enhance the emission intensity of LGO by a factor of 11.02 originating from the appropriate ionic size and coordination mode. Besides, the LPL time of LGO:Cu2+ can be extended effectively to 2 h by adjusting the sintering temperature and time (900 °C@24 h). The extension mechanism is that Li and Ga can be substituted for each other more easily and induce crystal structure distortion due to the special crystal structure of LGO, resulting in an optimal trap concentration in LGO:Cu2+. Thus, our findings provide a simple way to modulate long persistent luminescence and further consider their potential impact on optical information encryption.

Dual-Phase Glass Ceramics Containing ZnGa2O4:Cr3+ and NaYF4:Yb3+,Er3+ Nanocrystals for Dual-Mode Optical Thermometry.

Currently, developing luminescent materials for dual-mode optical thermometry has been becoming a rising topic, and concurrent temperature-sensitive optical parameters hold the key. Still, it is a serious challenge, since distinct activators are generally needed and energy transfer (ET) processes among activators inevitably occur, further leading to severe luminescence quenching. Herein, a spatial separation strategy is proposed for designing dual-phase glass ceramics (GCs) containing ZnGa2O4:Cr3+ and NaYF4:Yb3+,Er3+ nanocrystals (NCs) for dual-mode optical thermometry, in order to integrate diversified activators into one. Structural, morphological, and optical characterizations are examined to verify the partition of Cr3+ into ZnGa2O4 and Er3+ into the NaYF4 lattice in the dual-phase GC. Benefiting from such a spatial separation strategy, the adverse ET processes between Cr3+ and Er3+ could be cut off in the dual-phase GC, contributing to downshifting (DS) and upconversion (UC) luminescence. Furthermore, dual-mode optical thermometry is performed based on the lifetime of Cr3+ and fluorescence intensity ratio (FIR) of Er3+, with high relative sensitivities of 0.95% K-1@450 K and 1.24% K-1@303 K, respectively. It is evidenced that the dual-phase GC holds great potential for dual-mode optical thermometry, and this work also offers a prospective pathway for expanding the practical applications of GC luminescent materials.

Hydrofluoric Acid-Free Broadband Near-Infrared Phosphors K2LiMF6:Cr3+ with Zero-Thermal Quenching: Structure, Luminescence, and Application.

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are considered promising light sources for night vision, food analysis, biomedicine, and plant growth. Yet, the application potential of this technology is vulnerable to the function degradation of the phosphors used, such as thermal quenching, which needs to be addressed urgently. Herein, the NIR phosphors K2LiMF6:Cr3+ (M = Al, Ga, In) with a cubic double-perovskite structure synthesized by a green hydrofluoric acid-free hydrothermal method exhibit outstanding thermal stability. Under 450 nm excitation, the as-synthesized K2LiMF6:Cr3+ phosphors all exhibited broadband NIR emission covering 650-1000 nm peaking at 755-780 nm. The prepared K2LiAlF6:Cr3+ phosphor shows a unique zero-thermal quenching performance (I423 K/I298 K = 102%). The comprehensive effects of a wide band gap, large thermal energy barrier, weak electron-phonon coupling effect, and high structural rigidity are responsible for the suppression of thermal quenching in this material. The output power of the NIR pc-LED device reached 285 mW at 100 mA. This series of phosphors has promise in night vision and bioimaging applications.

Advanced photocatalytic disinfection mechanisms and their challenges.

Currently, microbial contamination issues have globally brought out a huge health threat to human beings and animals. To be specific, microorganisms including bacteria and viruses display durable ecological toxicity and various diseases to aquatic organisms. In the past decade, the photocatalytic microorganism inactivation technique has attracted more and more concern owing to its green, low-cost, and sustainable process. A variety kinds of photocatalysts have been employed for killing microorganisms in the natural environment. However, two predominant shortcomings including low activity of photocatalysts and diverse impacts of water characteristics are still displayed in the current photocatalytic disinfection system. So far, various strategies to improve the inherent activity of photocatalysts. Other than the modification of photocatalysts, the optimization of environments of water bodies has been also conducted to enhance microorganisms inactivation. In this mini-review, we outlined the recent progress in photocatalytic sterilization of microorganisms. Meanwhile, the relevant methods of photocatalyst modification and the influences of water body characteristics on disinfection ability were thoroughly elaborated. More importantly, the relationships between strategies for constructing advanced photocatalytic microorganism inactivation systems and improved performance were correlated. Finally, the perspectives on the prospects and challenges of photocatalytic disinfection were presented. We sincerely hope that this critical mini-review can inspire some new concepts and ideas in designing advanced photocatalytic disinfection systems.

Cs3Bi2Br9 nanoparticles decorated C3N4 nanotubes composite photocatalyst for highly selective oxidation of benzylic alcohol.

Solar-light driven oxidation of benzylic alcohols over photocatalysts endows significant prospects in value-added organics evolution owing to its facile, inexpensive and sustainable process. However, the unsatisfactory performance of actual photocatalysts due to the inefficient charge separation, low photoredox potential and sluggish surface reaction impedes the practical application of this process. Herein, we developed an innovative Z-Scheme Cs3BiBr9 nanoparticles@porous C3N4 tubes (CBB-NP@P-tube-CN) heterojunction photocatalyst for highly selective benzyl alcohol oxidation. Such composite combining increased photo-oxidation potential, Z-Scheme charge migration route as well as the structural advantages of porous tubular C3N4 ensures the accelerated mass and ions diffusion kinetics, the fast photoinduced carriers dissociation and sufficient photoredox potentials. The CBB-NP@P-tube-CN photocatalyst demonstrates an exceptional performance for selective photo-oxidation of benzylic alcohol into benzaldehyde with 19, 14 and 3 times higher benzylic alcohols conversion rate than those of C3N4 nanotubes, Cs3Bi2Br9 and Cs3Bi2Br9@bulk C3N4 photocatalysts, respectively. This work offers a sustainable photocatalytic system based on lead-free halide perovskite toward large scale solar-light driven value-added chemicals production.

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.

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.

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.