Electronic conduction in La-based perovskite-type oxides

Abstract

A systematic study of La-based perovskite-type oxides from the viewpoint of their electronic conduction properties was performed. LaCo_0.5Ni_0.5O_3±δ was found to be a promising candidate as a replacement for standard metals used in oxide electrodes and wiring that are operated at temperatures up to 1173 K in air because of its high electrical conductivity and stability at high temperatures. LaCo_0.5Ni_0.5O_3±δ exhibits a high conductivity of 1.9 × 10³ S cm^?1 at room temperature (R.T.) because of a high carrier concentration n of 2.2 × 10²² cm^?3 and a small effective mass m? of 0.10 m_e. Notably, LaCo_0.5Ni_0.5O_3±δ exhibits this high electrical conductivity from R.T. to 1173 K, and little change in the oxygen content occurs under these conditions. LaCo_0.5Ni_0.5O_3±δ is the most suitable for the fabrication of oxide electrodes and wiring, though La_1?xSr_xCoO_3±δ and La_1?xSr_xMnO_3±δ also exhibit high electronic conductivity at R.T., with maximum electrical conductivities of 4.4 × 10³ S cm^?1 for La_0.5Sr_0.5CoO_3±δ and 1.5 × 10³ S cm^?1 for La_0.6Sr_0.4MnO_3±δ because oxygen release occurs in La_1?xSr_xCoO_3±δ as elevating temperature and the electrical conductivity of La_0.6Sr_0.4MnO_3±δ slightly decreases at temperatures above 400 K.     

MoOx thin films deposited by magnetron sputtering as an anode for aqueous micro-supercapacitors

Abstract

In order to examine the potential application of non-stoichiometric molybdenum oxide as anode materials for aqueous micro-supercapacitors, conductive MoO_x films (2  x  2.3) deposited via RF magnetron sputtering at different temperatures were systematically studied for composition, structure and electrochemical properties in an aqueous solution of Li₂SO₄. The MoO_x (x ≈ 2.3) film deposited at 150 °C exhibited a higher areal capacitance (31 mF cm^?2 measured at 5 mV s^?1), best rate capability and excellent stability at potentials below ?0.1 V versus saturated calomel electrode, compared to the films deposited at room temperature and at higher temperatures. These superior properties were attributed to the multi-valence composition and mixed-phase microstructure, i.e., the coexistence of MoO₂ nanocrystals and amorphous MoO_x (2.3 < x  3). A mechanism combining Mo(IV) oxidation/reduction on the hydrated MoO₂ grain surfaces and cation intercalation/extrusion is proposed to illustrate the pseudo-capacitive process.     

A high-performance integrated single-photon detector for telecom wavelengths

Abstract

A commercial avalanche photodiode (APD) and the circuitry needed to operate it as a single-photon detector (SPD) have been integrated onto a single PC board (PCB). At temperatures accessible with Peltier coolers (～200–240 K), the PCB-SPD achieves high detection efficiency (DE) at 1308 and 1545 nm with low dark-count probability (e.g. ～10^?6/bias pulse at DE = 20%, 220 K), making it useful for quantum key distribution (QKD). The board generates fast bias pulses, cancels noise transients, amplifies the signals, and sends them to an on-board discriminator. A digital blanking circuit suppresses afterpulsing.     

New Materials for Tunable Lasers in the Near Infrared

Abstract

There has been considerable recent effort aimed at realising tunable near-infrared laser action in solid-state media. Beyond 1 μm Ni²⁺ and Co²⁺ emissions have been mainly studied, and laser action has been achieved in several materials doped with these ions although usually only at low temperatures. Luminescence from Co²⁺ and Ni²⁺ in the host material LiGa₅O₈ is described and evidence is presented for a high quantum efficiency, even up to room temperature. We describe also the results of our lifetime and luminescence measurements on the various active centres in the Mg₂SiO₄: Cr laser system.     

Versatile Indolocarbazole‐Isomer Derivatives as Highly Emissive Emitters and Ideal Hosts for Thermally Activated Delayed Fluorescent OLEDs with Alleviated Efficiency Roll‐Off

Maintaining high efficiency at high brightness levels is an exigent challenge for real‐world applications of thermally activated delayed fluorescent organic light‐emitting diodes (TADF‐OLEDs). Here, versatile indolocarbazole‐isomer derivatives are developed as highly emissive emitters and ideal hosts for TADF‐OLEDs to alleviate efficiency roll‐off. It is observed that photophysical and electronic properties of these compounds can be well modulated by varying the indolocarbazole isomers. A photoluminescence quantum yield (η_PL) approaching unity and a maximum external quantum efficiency (EQE_max) of 25.1% are obtained for the emitter with indolo[3,2‐a]carbazolyl subunit. Remarkably, record‐high EQE/power efficiency of 26.2%/69.7 lm W^?1 at the brightness level of 5000 cd m^?2 with a voltage of only 3.74 V are also obtained using the same isomer as the host in a green TADF‐OLED. It is evident that TADF hosts with high η_PL values, fast reverse intersystem crossing processes, and balanced charge transport properties may open the path toward roll‐off‐free TADF‐OLEDs.     

Spontaneous Formation of Noble‐ and Heavy‐Metal‐Free Alloyed Semiconductor Quantum Rods for Efficient Photocatalysis

Quasi‐1D cadmium chalcogenide quantum rods (QRs) are benchmark semiconductor materials that are combined with noble metals to constitute QR heterostructures for efficient photocatalysis. However, the high toxicity of cadmium and cost of noble metals are the main obstacles to their widespread use. Herein, a facile colloidal synthetic approach is reported that leads to the spontaneous formation of cadmium‐free alloyed ZnS_xSe_1?x QRs from polydisperse ZnSe nanowires by alkylthiol etching. The obtained non‐noble‐metal ZnS_xSe_1?x QRs can not only be directly adopted as efficient photocatalysts for water oxidation, showing a striking oxygen evolution capability of 3000 µmol g^?1 h^?1, but also be utilized to prepare QR‐sensitized TiO₂ photoanodes which present enhanced photo‐electrochemical (PEC) activity. Density functional theory (DFT) simulations reveal that alloyed ZnS_xSe_1?x QRs have highly active Zn sites on the (100) surface and reduced energy barrier for oxygen evolution, which in turn, are beneficial to their outstanding photocatalytic and PEC activities.     

Robustness of homodyne tomography to phase-insensitive noise

Abstract

We study the effects of phase-insensitive noise on homodyne measurements of a radiation density matrix. We prove that this noise has an effect equivalent to a non-unit quantum efficiency at detectors. The overall effective quantum efficiency η_? of the measurement is evaluated in terms of the quantum efficiency at detectors and of the average number of noise photons added to the radiation field. For pure Gaussian-displacement noise, we show that half a photon of noise is enough to prevent the homodyne measurement of the density matrix.     

Extremely Small Pyrrhotite Fe7S8 Nanocrystals with Simultaneous Carbon‐Encapsulation for High‐Performance Na–Ion Batteries

Na/FeS_x batteries have remarkable potential applicability due to their high theoretical capacity and cost‐effectiveness. However, realization of high power‐capability and long‐term cyclability remains a major challenge. Herein, ultrafine Fe₇S₈@C nanocrystals (NCs) as a promising anode material for a Na–ion battery that addresses the above two issues simultaneously is reported. An Fe₇S₈ core with quantum size (≈10 nm) overcomes the kinetic and thermodynamic constraints of the Na‐S conversion reaction. In addition, the high degree of interconnection through carbon shells improves the electronic transport along the structure. As a result, the Fe₇S₈@C NCs electrode achieves excellent power capability of 550 mA h g^?1 (≈79% retention of its theoretical capacity) at a current rate of 2700 mA g^?1. Furthermore, a conformal carbon shell acts as a buffer layer to prevent severe volume change, which provides outstanding cyclability of ≈447 mA h g^?1 after 1000 cycles (≈71% retention of the initial charge capacity).     

Ultrasensitive Surface‐Enhanced Raman Spectroscopy Detection Based on Amorphous Molybdenum Oxide Quantum Dots

Surface‐enhanced Raman spectroscopy (SERS) based on plasmonic semiconductive material has been proved to be an efficient tool to detect trace of substances, while the relatively weak plasmon resonance compared with noble metal materials restricts its practical application. Herein, for the first time a facile method to fabricate amorphous H_xMoO₃ quantum dots with tunable plasmon resonance is developed by a controlled oxidization route. The as‐prepared amorphous H_xMoO₃ quantum dots show tunable plasmon resonance in the region of visible and near‐infrared light. Moreover, the tunability induced by SC CO₂ is analyzed by a molecule kinetic theory combined with a molecular thermodynamic model. More importantly, the ultrahigh enhancement factor of amorphous H_xMoO₃ quantum dots detecting on methyl blue can be up to 9.5 × 10⁵ with expending the limit of detection to 10^?9 m . Such a remarkable porperty can also be found in this H_xMoO₃‐based sensor with Rh6G and RhB as probe molecules, suggesting that the amorphous H_xMoO₃ quantum dot is an efficient candidate for SERS on molecule detection in high precision.     

Photoluminescence properties of AlxGa1−x As epitaxial layers grown under conditions of ultrafast flux cooling

Results are presented of studies of the photoluminescence properties of epitaxial layers of Al_xGa_1−x As solid solutions grown by liquid-phase epitaxy with nonequilibrium crystallization achieved by ultrafast rates of cooling of the flux (V∼10²–10³ °C/s). The photoluminescence characteristics obtained indicate that the epitaxial layers are of high quality. It is also observed that when samples with x _buff=0.5–0.55 are exposed to laser radiation of power density ∼1 kW/cm² at a temperature of 77 K, the spectral composition of the radiation undergoes irreversible changes caused by the formation of an arsenic vacancy (V _As)-donor impurity complex. Pis’ma Zh. Tekh. Fiz. 23, 8–13 (March 12, 1997)     

Spin‐Orbit Torque Switching of a Nearly Compensated Ferrimagnet by Topological Surface States

Utilizing spin‐orbit torque (SOT) to switch a magnetic moment provides a promising route for low‐power‐dissipation spintronic devices. Here, the SOT switching of a nearly compensated ferrimagnet Gd_x(FeCo)_1?x by the topological insulator [Bi₂Se₃ and (BiSb)₂Te₃] is investigated at room temperature. The switching current density of (BiSb)₂Te₃ (1.20 × 10⁵ A cm^?2) is more than one order of magnitude smaller than that in conventional heavy‐metal‐based structures, which indicates the ultrahigh efficiency of charge‐spin conversion (>1) in topological surface states. By tuning the net magnetic moment of Gd_x(FeCo)_1?x via changing the composition, the SOT efficiency has a significant enhancement (6.5 times) near the magnetic compensation point, and at the same time the switching speed can be as fast as several picoseconds. Combining the topological surface states and the nearly compensated ferrimagnets provides a promising route for practical energy‐efficient and high‐speed spintronic devices.     

High‐Stability MnOx Nanowires@C@MnOx Nanosheet Core–Shell Heterostructure Pseudocapacitance Electrode Based on Reversible Phase Transition Mechanism

A stable MnO_x@C@MnO_x core–shell heterostructure consisting of vertical MnO_x nanosheets grown evenly on the surface of the MnO_x@carbon nanowires are obtained by simple liquid phase method combined with thermal treatment. The hierarchical MnO_x@C@MnO_x heterostructure electrode possesses a high specific capacitance of 350 F g^?1 and an excellent cycle performance owing to the existence of the pore structure among the ultrasmall MnO_x nanoparticles and the rapid transmission of electrons between the active material and carbon coating layer. Particularly, according to the in situ Raman spectra analysis, no characteristic peaks corresponding to MnOOH are found during charging/discharging, indicating that pseudocapacitive behavior of the MnO_x electrode have no relevance to the intercalation/deintercalation of protons (H⁺) in the electrolyte. Further combining in situ X‐ray powder diffraction analysis, the diffraction peak of α‐MnO₂ can be detected in the process of charging, while Mn₃O₄ phase is found in discharge products. Therefore, these results demonstrate that the MnO_x undergoes a reversible phase transformation reaction of Mn₃O₄?α‐MnO₂. Moreover, the assembled all‐solid‐state asymmetric supercapacitor with a MnO_x@C@MnO_x electrode delivers a high energy density of 23 Wh kg^?1, an acceptable power density of 2500 W kg^?1, and an excellent cyclic stability performance of 94% after 2000 cycles, showing the potential for practical application.     

Surface Coating Constraint Induced Anisotropic Swelling of Silicon in Si–Void@SiO x Nanowire Anode for Lithium‐Ion Batteries

Here a simple and an environmentally friendly approach is developed for the fabrication of Si–void@SiO_x nanowires of a high‐capacity Li‐ion anode material. The outer surface of the robust SiO_x backbone and the inside void structure in Si–void@SiO_x nanowires appropriately suppress the volume expansion and lead to anisotropic swelling morphologies of Si nanowires during lithiation/delithiation, which is first demonstrated by the in situ lithiation process. Remarkably, the Si–void@SiO_x nanowire electrode exhibits excellent overall lithium‐storage performance, including high specific capacity, high rate property, and excellent cycling stability. A reversible capacity of 1981 mAh g^?1 is obtained in the fourth cycle, and the capacity is maintained at 2197 mAh g^?1 after 200 cycles at a current density of 0.5 C. The outstanding overall properties of the Si–void@SiO_x nanowire composite make it a promising anode material of lithium‐ion batteries for the power‐intensive energy storage applications.     

High-power 1.8-μm InGaAsP/InP lasers

Separately bounded InGaAsP/InP laser heterostructures with two stressed quantum wells emitting at a wavelength of 1.8 μm were obtained by metalorganic vapor-phase epitaxy. The laser diodes with a strip width of 100 μm provide for an output radiation power of 1.2 W in the continuous operation mode at a temperature of 20°C. A minimum threshold current density was 320 A/cm² and a differential quantum efficiency was η_d=28% for a Fabry-Perot resonator length of 1.4 mm. The internal optical losses in the laser heterostructure studied amounted to 5.6 cm^?1.     

Hybrid Perovskite Light‐Emitting Diodes Based on Perovskite Nanocrystals with Organic–Inorganic Mixed Cations

Organic–inorganic hybrid perovskite materials with mixed cations have demonstrated tremendous advances in photovoltaics recently, by showing a significant enhancement of power conversion efficiency and improved perovskite stability. Inspired by this development, this study presents the facile synthesis of mixed‐cation perovskite nanocrystals based on FA_{(1?x )}Cs_x PbBr₃ (FA = CH(NH₂)₂). By detailed characterization of their morphological, optical, and physicochemical properties, it is found that the emission property of the perovskite, FA_{(1?x )}Cs_x PbBr₃, is significantly dependent on the substitution content of the Cs cations in the perovskite composition. These mixed‐cation perovskites are employed as light emitters in light‐emitting diodes (LEDs). With an optimized composition of FA_0.8Cs_0.2PbBr₃, the LEDs exhibit encouraging performance with a highest reported luminance of 55 005 cd m^?2 and a current efficiency of 10.09 cd A^?1. This work provides important instructions on the future compositional optimization of mixed‐cation perovskite for obtaining high‐performance LEDs. The authors believe this work is a new milestone in the development of bright and efficient perovskite LEDs.     

Oxygen‐Vacancy and Surface Modulation of Ultrathin Nickel Cobaltite Nanosheets as a High‐Energy Cathode for Advanced Zn‐Ion Batteries

The development of high‐capacity, Earth‐abundant, and stable cathode materials for robust aqueous Zn‐ion batteries is an ongoing challenge. Herein, ultrathin nickel cobaltite (NiCo₂O₄) nanosheets with enriched oxygen vacancies and surface phosphate ions (P–NiCo₂O_4‐x) are reported as a new high‐energy‐density cathode material for rechargeable Zn‐ion batteries. The oxygen‐vacancy and surface phosphate‐ion modulation are achieved by annealing the pristine NiCo₂O₄ nanosheets using a simple phosphating process. Benefiting from the merits of substantially improved electrical conductivity and increased concentration of active sites, the optimized P–NiCo₂O_4‐x nanosheet electrode delivers remarkable capacity (309.2 mAh g^?1 at 6.0 A g^?1) and extraordinary rate performance (64% capacity retention at 60.4 A g^?1). Moreover, based on the P–NiCo₂O_4‐x cathode, our fabricated P–NiCo₂O_4‐x//Zn battery presents an impressive specific capacity of 361.3 mAh g^?1 at the high current density of 3.0 A g^?1 in an alkaline electrolyte. Furthermore, extremely high energy density (616.5 Wh kg^?1) and power density (30.2 kW kg^?1) are also achieved, which outperforms most of the previously reported aqueous Zn‐ion batteries. This ultrafast and high‐energy aqueous Zn‐ion battery is promising for widespread application to electric vehicles and intelligent devices.     

A Phosphanthrene Oxide Host with Close Sphere Packing for Ultralow‐Voltage‐Driven Efficient Blue Thermally Activated Delayed Fluorescence Diodes

A phosphanthrene oxide host, 5,10‐diphenyl‐phosphanthrene 5,10‐dioxide ( DPDPO₂A ), with intra‐ and intermolecular hydrogen bonds achieves spheroidal cis ‐configuration and close sphere packing. DPDPO₂A realizes effective exciton suppression and excellent and balanced carrier transporting ability, both at the same time, demonstrating favorable photoluminescence quantum yield of 84% from its blue thermally activated delayed fluorescence (TADF) dye, namely bis[4‐(9,9‐dimethyl‐9,10‐dihydroacridine) phenyl]sulfone, doped films and high electron and hole mobility at the level of 10^?4 and 10^?5 cm² V^?1 s^?1, respectively. DPDPO₂A endows its blue TADF devices with record‐low driving voltages, e.g., turn‐on voltage of 2.5 V, and the state‐of‐the‐art efficiencies with maxima of 22.5% for external quantum efficiency and 52.9 lm W^?1 for power efficiency, which is the best comprehensive performance to date of ultralow‐voltage‐driven blue TADF diodes.     

Anionic Se‐Substitution toward High‐Performance CuS1−xSex Nanosheet Cathode for Rechargeable Magnesium Batteries

Rechargeable magnesium batteries (rMBs) are promising as the most ideal further energy storage systems but lack competent cathode materials due to sluggish redox reaction kinetics. Herein, developed is an anionic Se‐substitution strategy to improve the rate capability and the cycling stability of 2D CuS_1?xSe_x nanosheet cathodes through an efficient microwave‐induced heating method. The optimized CuS_1?xSe_x (X = 0.2) nanosheet cathode can exhibit high reversible capacity of 268.5 mAh g^?1 at 20 mA g^?1 and good cycling stability (140.4 mAh g^?1 at 300 mA g^?1 upon 100 cycles). Moreover, the CuS_1?xSe_x (X = 0.2) nanosheet cathode can deliver remarkable rate capability with a reversible capacity of 119.2 mAh g^?1 at 500 mA g^?1, much higher than the 21.7 mAh g^?1 of pristine CuS nanosheets. The superior electrochemical performance can be ascribed to the enhanced reaction kinetics, enriched cation storage active sites, and shortened ion diffusion pathway of the CuS_1?xSe_x nanosheet. Therefore, tuning anionic chemical composition demonstrates an effective strategy to develop novel cathode materials for rMBs.     

Flexible Broadband Graphene Photodetectors Enhanced by Plasmonic Cu3−xP Colloidal Nanocrystals

The integration of graphene with colloidal quantum dots (QDs) that have tunable light absorption affords new opportunities for optoelectronic applications as such a hybrid system solves the problem of both quantity and mobility of photocarriers. In this work, a hybrid system comprising of monolayer graphene and self‐doped colloidal copper phosphide (Cu_3?x P) QDs is developed for efficient broadband photodetection. Unlike conventional PbS QDs that are toxic, Cu_3?x P QDs are environmental friendly and have plasmonic resonant absorption in near‐infrared (NIR) wavelength. The half‐covered graphene with Cu_3?x P nanocrystals (NCs) behaves as a self‐driven p–n junction and shows durable photoresponse in NIR range. A comparison experiment reveals that the surface ligand attached to Cu_3?x P NCs plays a key role in determining the charge transfer efficiency from Cu_3?x P to graphene. The most efficient three‐terminal photodetectors based on graphene‐Cu_3?x P exhibit broadband photoresponse from 400 to 1550 nm with an ultrahigh responsivity (1.59 × 10⁵ A W^?1) and high photoconductive gain (6.66 × 10⁵) at visible wavelength (405 nm), and a good responsivity of 9.34 A W^?1 at 1550 nm. The demonstration of flexible graphene‐Cu_3?x P photodetectors operated at NIR wavelengths may find potential applications in optical sensing, biological imaging, and wearable devices.     

Effective lattice stabilization of gadolinium aluminate garnet (GdAG) via Lu3+ doping and development of highly efficient (Gd,Lu)AG:Eu3+ red phosphors

Abstract

The metastable garnet lattice of Gd₃Al₅O₁₂ is stabilized by doping with smaller Lu³⁺, which then allows an effective incorporation of larger Eu³⁺ activators. The [(Gd_1?xLu_x)_1?yEu_y]₃Al₅O₁₂ (x = 0.1–0.5, y = 0.01–0.09) garnet solid solutions, calcined from their precursors synthesized via carbonate coprecipitation, exhibit strong luminescence at 591 nm (the ⁵D₀ → ⁷F₁ magnetic dipole transition of Eu³⁺) upon UV excitation into the charge transfer band (CTB) at ～239 nm, with CIE chromaticity coordinates of x = 0.620 and y = 0.380 (orange-red). The quenching concentration of Eu³⁺ was estimated at ～5 at.% (y = 0.05), and the quenching was attributed to exchange interactions. Partial replacement of Gd³⁺ with Lu³⁺ up to 50 at.% (x = 0.5) while keeping Eu³⁺ at the optimal content of 5 at.% does not significantly alter the peak positions of the CTB and ⁵D₀ → ⁷F₁ emission bands but slightly weakens both bands owing to the higher electronegativity of Lu³⁺. The effects of processing temperature (1000–1500 °C) and Lu/Eu contents on the intensity, quantum efficiency, lifetime and asymmetry factor of luminescence were thoroughly investigated. The [(Gd_0.7Lu_0.3)_0.95Eu_0.05]₃Al₅O₁₂ phosphor processed at 1500 °C exhibits a high internal quantum efficiency of ～83.2% under 239 nm excitation, which, in combination with the high theoretical density, favors its use as a new type of photoluminescent and scintillation material.