Enhancing humidity resistance of nickel-rich layered cathode materials by low water-soluble CaF2 coating.

A low water-solubility but hydrophilic coating of CaF2 is demonstrated to be effective in mitigating the susceptibility of nickel-rich cathodes to moisture and even water. The ability of the cathode to resist water erosion is not inherently linked to either hydrophobicity or hydrophilicity, but lies in robust chemical bonding within the protective layer exhibiting low water solubility.

Unlocking the critical roles of N, P Co-Doping in MXene for Lithium-Oxygen Batteries: Elevated d-Band center and expanded interlayer spacing.

The design and fabrication of bifunctional catalysts with high electrocatalytic activity and stability are critical for developing highly reversible Li-O2 batteries (LOBs). Herein, the N, P co-doped MXene (NP-MXene) is prepared by one-step annealing method and evaluated as bifunctional catalyst for LOBs. The results suggest that the P doping plays a crucial role in increasing interlayer distance of MXene, thereby effectively providing more active sites, fast mass transfer, and ample space for the deposition/decomposition of Li2O2. Moreover, the N doping can significantly elevate the d-band center of Ti, thereby remarkably improving the adsorption of reaction intermediates and accelerating the deposition/decomposition of Li2O2 films. Consequently, the MXene-based LOBs deliver an ultrahigh specific capacity of 13,995 mAh/g at 500 mA g-1, a discharge/charge voltage gap of 0.89 V, and a cycle life up to 523 cycles with a limited capacity of 1000 mAh/g at 500 mA g-1. Impressively, the as-fabricated flexible LOBs with NP-MXene cathode display excellent cycling stability and ability to continuously power LEDs even after bending. Our findings pave the road of heteroatom doped MXenes as next-generation electrodes for high-performance energy storage and conversion systems.

Origin of the Cr3+ concentration-dependent broadband near-infrared emission in Sc2Si2O7.

The challenge of developing phosphors with tailored near-infrared (NIR) emission ranges to meet the diverse demands of various applications is a paramount concern in the contemporary realm of NIR phosphor research. A strong dependence of NIR emission on Cr3+ concentration has been demonstrated in Sc2-xSi2O7:xCr3+, which exhibits an NIR emission band at 840 nm for low Cr3+ doping concentrations (x = 0.001-0.01) and an anomalous NIR emission band at 1300 nm for high Cr3+ doping concentrations (x = 0.01-0.10). Careful investigation of the crystal structure, excitation and emission spectra, and luminescence decay curves indicates that the two NIR emissions can be attributed to the isolated Cr3+ ions and the Cr3+-Cr3+ pairs, respectively. The strong interaction of exchange-coupled Cr3+-Cr3+ pairs is supported by temperature-dependent emission spectra, luminescence decay curves and electron paramagnetic resonance (EPR) measurements. This work provides a new insight into the study of Cr3+-Cr3+ pairs for broadband NIR emission.

Thermal stability and quantum efficiency improvement of Cr3+-activated garnet phosphors via regulating A/B sites for near-infrared LED applications.

The discovery of phosphors with highly efficient broadband near-infrared emission is urgent for constructing NIR sources for various applications. Herein, we synthesized a series of near-infrared emitting garnet-type (A3B2C3O12) Lu2-xCaAl3.99Cr0.01SiO12:xGd/La and Lu2CaAl3.99-yCr0.01SiO12:ySc/Ga phosphors and systematically investigated the effect of A/B-site substitution on the crystal structure and luminescence properties. Structural and optical analyses revealed that the A/B-site substitution weakened the crystal field strength, further enhancing the broadband emission of the allowed 4T2 → 4A2transition and diminishing the narrow-peak emission of the forbidden 2E → 4A2 transition. As expected, NIR phosphors, exemplified by Lu1.7CaAl3.99Cr0.01SiO12:0.3Gd and Lu2CaAl3.49Cr0.01SiO12:0.5Sc, showed outstanding thermal stabilities at 423 K (150 °C) registering values of 103.02% and 94.91%, with high quantum efficiencies of 80.48% and 85.01%, respectively. In addition, pc-LEDs with broadband NIR output and good optoelectronic properties have been realized, demonstrating the great potential of broadband NIR pc-LEDs for applications. This work not only provides a series of high-efficiency phosphors for NIR pc-LED applications, but also provides a systematic idea and an efficient method to improve the luminescence performance of garnet-type phosphors.

An electrospun three-layer nanofibrous membrane-based in situ gel separator for efficient lithium-organic batteries.

An in situ gel separator based on an electrospun three-layer nanofibrous membrane (PSE11-Gel) is developed for high-performance lithium-organic batteries (LOBs). The highly efficient shuttle effect inhibition of organic cathode molecules or lithiated intermediates has been demonstrated for PSE11-Gel to realize high-capacity stable LOBs.

The Creation of Multimode Luminescent Phosphor through an Oxygen Vacancy Center for High-Level Anticounterfeiting.

Integrating multimode optical properties into a single material simultaneously is promising for improving the security level of fluorescent anticounterfeiting. However, there has been a lack of affirmative principles and unambiguous mechanisms that guide the design of such material. Herein, we achieve color-tunable photoluminescence, long-lived persistent emission, thermally stimulated luminescence, and reversible photochromism in a Tb3+-activated Mg4Ga8Ge2O20 phosphor by employing the F-like color center as an energy reservoir. It is experimentally revealed that the role of oxygen vacancies in the lattice of Mg4Ga8Ge2O20 is assumed as the main trap for the photogenerated electronic carriers, which is the origin of metastable F-like color centers. The formed color centers with the estimated depths of 0.48-0.95 eV could suppress the recombination of electron-hole pairs, thus giving rise to good photochromism and persistent emission properties, while under various modes of stimulation such as thermal attack or photo radiation, a quick recombination of electron holes happens, accounting for the bright thermally stimulated luminescence and the accompanied color bleaching. Finally, we fabricate a flexible phosphor/polymer composite by encapsulating the developed phosphor into a polydimethylsiloxane matrix, and conceptual demonstration of the composite for the high-security fluorescent anticounterfeiting technology, by virtue of multimode optical phenomena as authentication signals.

4-Electron redox enabled by a perylene diimide containing side-chain amines for efficient organic cathode development.

A perylene diimide containing side-chain amines (PDIN) was studied as an organic cathode for application in lithium batteries, showing a high capacity of 174 mA h g-1. The chemical structures, experimental results, and calculation analyses verify that PDIN performed a 4-electron redox reaction jointly involving its CO and side-chain amine groups. This study promotes the development of organic cathodes with multi-electron redox reactions.

Influence of framework disordering on the luminescence performance of Cr3+-doped near-infrared phosphors: a case study of A3B6O14-type hosts.

The luminescence efficiency and thermal stability are enduring topics in the realm of phosphors. It is acknowledged that the structural transformation from disorder to order results in increased lattice rigidity, consequently inducing heightened efficiency and enhanced thermal stability. In this case study of the structural evolution of Ca3Ga2Ge4O14:Cr3+, NaCa2GaGe5O14:Cr3+ and Na2CaGe6O14:Cr3+ near-infrared (NIR) phosphors, a significant paradox is revealed: the incongruent relationship between the fluctuating degrees of disorder and the simultaneous improvements in efficiency and thermal stability. By drawing on insights gained from structural analysis, optical investigations, and theoretical calculations, a notable revelation surfaces: the primary factor affecting rigidity and optical performance is not the disordering of the entire lattice, but rather the disordering of the framework itself. The findings elucidate the principle of framework-order engineering for crafting high-performance NIR phosphors.

Improved Thermal and Chemical Stability of Oxynitride Phosphor from Facile Chemical Synthesis for Vehicle Cornering Lights.

Orange Eu2+ -doped phosphors are essential for light-emitting diodes for cornering lights to prevent fatal road accidents at night, but such phosphors require features of high thermal, chemical stability and facile synthesis. This study reports a series of yellow-orange-red emitting SrAl2 Si3 ON6 :Eu2+ oxynitride phosphors, derived from the SrAlSi4 N7 nitride iso-structure by replacing Si4+ -N3- with Al3+ -O2- . The introduction of a certain amount of oxygen enabled the facile synthesis under atmospheric pressure using the air-stable raw materials SrCO3 , Eu2 O3 , AlN and Si3 N4 . SrAl2 Si3 ON6 has a smaller band gap and lower structure rigidity than SrAlSi4 N7 (5.19 eV vs 5.50 eV, Debye temperature 719 K vs 760 K), but exhibits higher thermal stability with 100 % of room temperature intensity remaining at 150 °C compared to 85 % for SrAlSi4 N7 . Electron paramagnetic resonance, thermoluminescence and density functional theory revealed that the oxygen vacancy electron traps compensated the thermal loss. Additionally, no decrease in emission intensity was found after either being heated at 500 °C for 2 hours or being immersed in water for 20 days, implying both of the thermal and chemical stability of SrAl2 Si3 ON6 :Eu2+ phosphors. The strategy of oxynitride-introduction from nitride promotes the development of low-cost thermally and chemically stable luminescent materials.

Highly efficient CsPbBr3@glass@polyurethane composite film as flexible liquid crystal display backlight.

Inorganic lead halide perovskite quantum dots (CsPbX3 QDs (X = Cl, Br, or I)) have attracted more and more attention due to their high absorption coefficient, narrow emission band, high quantum efficiency, and tunable emission wavelength. However, CsPbX3 QDs are decomposed when exposed to bright light, heat, moisture, etc., which leads to severe luminous attenuation and limits their commercial application. In this paper, CsPbBr3@glass materials were successfully synthesized by a one-step self-crystallization method, including melting, quenching and heat treatment processes. The stability of CsPbBr3 QDs was improved by embedding CsPbBr3 QDs into zinc-borosilicate glass. Then, the CsPbBr3@glass was combined with polyurethane (PU) to form a flexible composite luminescent film CsPbBr3@glass@PU. This strategy enables the transformation of rigid perovskite quantum dot glass into flexible luminescent film materials and further improves the photoluminescence quantum yield (PLQY) from 50.5% to 70.2%. The flexible film has good tensile properties, and its length can be strained 5 times as long as the original length. Finally, a white LED was encapsulated by combining CsPbBr3@glass@PU film and red phosphor K2SiF6:Mn4+ with a blue LED chip. The good performance of the obtained CsPbBr3@glass@PU film indicates that it has potential application in flexible liquid crystal displays (LCDs) as a backlight source.

Tetrahedrally coordinated rigid crystal structure enables partial self-reduction of mixed-valence europium for optical thermometric application.

Mixed-valence europium-activated phosphors are receiving attention in many fields, such as lighting, anti-counterfeiting, optical recording, encryption, and temperature sensing. However, it remains difficult to construct mixed-valence europium-activated compounds due to the reductive and oxidative synthesis conditions required to obtain Eu2+ and Eu3+ ions, respectively. Herein, mixed-valence Eu2+/Eu3+ was realized in the CaBPO5 built by rigidly connected BO4 and PO4 tetrahedrons by partial Eu3+ → Eu2+ self-reduction in the air atmosphere. Commendably, the CaBPO5:Eu2+/Eu3+ phosphor exhibits excellent ratiometric temperature sensing performance with the maximum absolute and relative sensitivity being as high as 0.184 K-1 and 3.444% K-1 with good signal discriminability, due to the high and low, respectively, temperature-dependence of Eu2+ and Eu3+ emissions. The rapid dropping intensity of Eu2+ in CaBPO5 with increasing temperature was due to the small energy gap (∼0.48 eV) between the Eu2+-5d state and the conduction band. Our work not only provides a novel thermometer candidate but also enlightens researchers to a method of effectively designing new mixed-valence metal-ion activated luminescent thermometers via selective tetrahedrally coordinated rigid crystal structure.

Near-UV excited multifunctional near-infrared phosphors for anti-counterfeiting and ratiometric thermometer applications.

Considerable efforts have been devoted to the development of visible light-emitting phosphors for anti-counterfeiting application, but the design of multifunctional near-infrared materials with suitable luminescent properties was lacking. Based on the crystal field theory, a near ultraviolet excitable and near-infrared emitting Ca2Sn2(1-x)Al2(1-x)O9:2xCr3+,2xSi4+ phosphor was designed. On the one hand, the Ca2Sn2(1-x)Al2(1-x)O9:2xCr3+,2xSi4+ phosphor showed great potential for applications including anti-counterfeiting and secret signals under a 405 nm near UV laser. The integrated intensity at 150 °C was 75.9%, implying high thermal stability when irradiated with a high power light source. On the other hand, an unexpected red emission component originating from the Cr3+-Cr3+ dimer was observed and was confirmed by fast luminescence decay and electron spin resonance signals. The different thermal stabilities of Cr3+ near-infrared and Cr3+-Cr3+ red emissions opened up a new opportunity for luminescence ratiometric thermometers.

Ultraviolet photodetector based on RbCu2I3microwire.

Copper-based halide perovskites have shown great potential in lighting and photodetection due to their excellent photoelectric properties, good stability and lead-free nature. However, as an important piece of copper-based perovskites, the synthesis and application of RbCu2I3have never been reported. Here, we demonstrate the synthesis of high-quality RbCu2I3microwires (MWs) by a fast-cooling hot saturated solution method. The prepared MWs exhibit an orthorhombic structure with a smooth surface. Optical measurements show the RbCu2I3MWs have a sharp ultraviolet absorption edge with 3.63 eV optical band gap and ultra-large stokes shift (300 nm) in photoluminescence. The subsequent photodetector based on a single RbCu2I3MW shows excellent ultraviolet detection performance. Under the 340 nm illumination, the device shows a specific detectivity of 5.0 × 109Jones and a responsivity of 380 mA·W-1. The synthesis method and physical properties of RbCu2I3could be a guide to the future optoelectronic application of the new material.

Superior thermal cycling stability of a carbon dots@NaBiF4 nanocomposite: facile synthesis and surface configurations.

Carbon dots (CDs), emerging as promising materials for optoelectronic and biomedical applications, are widely investigated due to their distinct merits of facile preparation, biocompatibility, and environment-friendliness. Here, a unique strategy based on surface engineering is proposed to modulate the photoluminescence (PL) of CDs in both aqueous solution and the solid state with good thermal cycling stability. For the typical blue emissive CD solution derived from citric acid and ethylenediamine, an intense green emission can be induced by adding Bi3+ due to the strong coordination ability of Bi3+ ions with carboxyl groups on the surface of CDs. A super facile synthesis approach (ultrafast at room-temperature) has been developed to fabricate the CDs@NaBiF4 nanocomposite, whose chemical structure and composition have been investigated in detail. For the solid nanocomposite, it not only preserves the strong blue emission from the intrinsic core state of CDs, but exhibits a new green emission from the surface state. The solid-state CDs@NaBiF4 nanocomposite exhibits good thermal stability and high resistance to thermal degradation under blue light excitation. The strategy via metal ion-mediated PL of CDs represents a new approach to control the optical properties of CDs, and provides more opportunities in solid-state lighting and biomedical applications.

Disorder-Order Conversion-Induced Enhancement of Thermal Stability of Pyroxene Near-Infrared Phosphors for Light-Emitting Diodes.

The minimization of thermal quenching, which leads to luminescence loss at high temperatures, is one of the most important issues for near-infrared phosphors. In the present work, we investigated the properties of near-infrared Ca(Sc,Mg)(Al, Si)O6 : Cr3+ phosphors with a pyroxene-type structure under blue light excitation. The CaScAlSiO6 : Cr3+ end member of Ca(Sc,Mg)(Al,Si)O6 : Cr3+ phosphor led to broadband emission at a full-width half maximum of 215 nm, whereas the CaMgSi2 O6 : Cr3+ end member exhibited high thermal stability at 150 °C, with an intensity of 88.4 % of that at room temperature. The structural analysis and density functional theory calculations revealed the absence of soft conformations and local space confinement contributed to the high structural rigidity and weakened the thermal quenching effect.

A novel Mn4+-activated layered oxide-fluoride perovskite-type KNaMoO2F4 red phosphor for wide gamut warm white light-emitting diode backlights.

Mn4+-activated oxide-fluoride phosphors are attractive for application in a wide range of solid-state lighting devices because of their distinct red emission at about 630 nm and the abundant storage of Mn ions. However, the zero-phonon line (ZPL) of Mn4+ ions is too weak to be detected in most host materials due to the magnetic dipole nature. In this article, we introduce a co-precipitation method for synthesizing a Mn4+-doped oxyfluoride perovskite KNaMoO2F4 phosphor containing [MoO2F4]2- building units. The electron paramagnetic resonance (EPR) spectra are consistent with the presence of a MnF62- species at g = 1.991. The KNaMoO2F4:0.01Mn4+ phosphor exhibits strong absorption under blue light and an internal quantum yield (IQE) of 65.8%. Attributed to the distorted octahedral environment of the Mn4+ ions, visible ZPL emission was detected at 625 nm. Based on theoretical calculations, the Mn4+ ions in the KNaMoO2F4 host exist in a strong crystal field with a high Dq/B value of ∼3.86. A series of photoluminescence-dependent low-temperature spectra indicates that the Mn4+ emissive state experiences weak electron-phonon interactions upon calculating the Huang-Rhys factor. Benefiting from the ZPL, a warm white-light-emitting diode is achieved using YAG:Ce3+ and KNaMoO2F4:Mn4+ as color converters, in which the color rendering index was Ra = 83.5 and CCT = 4490 K.

Orthorhombic Cobalt Ditelluride with Te Vacancy Defects Anchoring on Elastic MXene Enables Efficient Potassium-Ion Storage.

The fast and reversible potassiation/depotassiation of anode materials remains an elusive yet intriguing goal. Herein, a class of the P-doping-induced orthorhombic CoTe2 nanowires with Te vacancy defects supported on MXene (o-P-CoTe2 /MXene) is designed and prepared, taking advantage of the synergistic effects of the conductive o-P-CoTe2 arrays with rich Te vacancy defects and the elastic MXene sheets with self-autoadjustable function. Consequently, the o-P-CoTe2 /MXene superstructure exhibits boosted potassium-storage performance, in terms of high reversible capacity (373.7 mAh g-1 at 0.2 A g-1 after 200 cycles), remarkable rate capability (168.2 mAh g-1 at 20 A g-1 ), and outstanding long-term cyclability (0.011% capacity decay per cycle over 2000 cycles at 2 A g-1 ), representing the best performance in transition-metal-dichalcogenides-based anodes to date. Impressively, the flexible full battery with o-P-CoTe2 /MXene anode achieves a satisfying energy density of 275 Wh kg-1 and high bending stability. The kinetics analysis and first-principles calculations reveal superior pseudocapacitive property, high electronic conductivity, and favorable K+ ion adsorption and diffusion capability, corroborating fast K+ ion storage. Especially, ex situ characterizations confirm o-P-CoTe2 /MXene undergoes reversible evolutions of initially proceeding with the K+ ion insertion, followed by the conversion reaction mechanism.

Interface Engineering Ti3 C2 MXene/Silicon Self-Powered Photodetectors with High Responsivity and Detectivity for Weak Light Applications.

Interfacial engineering and heterostructures designing are two efficient routes to improve photoelectric characteristics of a photodetector. Herein, a Ti3 C2 MXene/Si heterojunction photodetector with ultrahigh specific detectivity (2.03 × 1013 Jones) and remarkable responsivity (402 mA W-1 ) at zero external bias without decline as with increasing the light power is reported. This is achieved by chemically regrown interfacial SiOx layer and the control of Ti3 C2 MXene thickness to suppress the dark noise current and improve the photoresponse. The photodetector demonstrates a high light on/off ratio of over 106 , an outstanding peak external quantum efficiency (EQE) of 60.3%, while it maintains an ultralow dark current at 0 V bias. Moreover, the device holds high performance with EQE of over 55% even after encapsulated with silicone, trying to resolve the air stability issue of Ti3 C2 MXene. Such a photodetector with high detectivity, high responsivity, and self-powered capability is particularly applicable to detect weak light signal, which presents high potential for imaging, communication and sensing applications.

Luminescence properties of Gd2MoO6:Eu3+ nanophosphors for WLEDs.

A series of Gd2-xMoO6:xEu3+ (x = 0.18-0.38) nanophosphors were synthesized by the solvothermal method. The properties of these nanophosphors were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), fluorescence spectroscopy and diffuse reflectance spectroscopy. Gd2-xMoO6:xEu3+ nanophosphors have a strong excitation band in the NUV region and emit red light with high color purity by efficient energy transfer from the MoO66- group to Eu3+ ions. Red LEDs and WLEDs were fabricated using a 370 nm chip and Gd2-xMoO6:0.26Eu3+ nanophosphors, which showed good electroluminescence performance. At a driving current of 20 mA, WLEDs displayed CIE coordinates of (0.3297, 0.3869), a correlated color temperature (CCT) of 5604 K and a high color rendering index (Ra) of 91.6. This work demonstrates that Gd2-xMoO6:xEu3+ phosphors are promising red phosphors excited by a NUV chip for WLEDs.

Mn4+-activated oxyfluoride K3TaOF6 red phosphor with intense zero phonon line for warm white light-emitting diodes.

The intense zero phonon line (ZPL) of the Mn4+:2E→4A2 transition can further promote the color rendering and luminous efficiency for high-quality white-emitting diodes (w-LEDs). In this article, a Mn4+-activated K3TaOF6 oxyfluoride red phosphor was synthesized via a facile two-step method. Its phase and morphology were characterized by X-ray diffraction, SEM and TEM. The as-prepared K3TaOF6:Mn4+ exhibits an intense absorption of blue light and a strong emission band peaking at 628 nm with a color purity as high as 96.4%. Attributed to the distorted octahedral coordination environment of Mn4+ ions, an intense ZPL emission was detected at 620 nm. By theoretical calculation, Mn4+ ions in the K3TaOF6 host experience a strong crystal field. In addition, the temperature-dependent PL and thermoluminescence (TL) spectra suggest that thermal ionization dominates the thermal quenching phenomenon in this phosphor.