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Using a green and convenient method to prepare fluoride red phosphor is an important challenge for industrialization applications. In this work, K2SiF6:Mn4+ red phosphor was successfully prepared through a brief one-step co-precipitation method without HF. A simplified and non-toxic ion exchange strategy for the formation of narrow-band red-emitting K2SiF6:Mn4+ phosphors was developed using different solvent (HAc, H3PO4, HNO3, HCl, H2O). The photoluminescence intensity of the prepared K2SiF6:Mn4+ red phosphor was the highest when the pH of the reaction solution was 1.0. Furthermore, using K2SiF6:Mn4+ as red component, the warm white light LED (light-emitting diode) with low correlated color temperature (CCT = 4095 K), high color rendering index (CRI, Ra = 87) was achieved, which proved that the phosphor synthesized by this method had great application potential. The preparation method provided in this article is safer and more environmentally friendly, and has important commercial and social value. [ABSTRACT FROM AUTHOR]

Ferroelectric photovoltaics, as a new type of solar cell, relying on an internal electric field instead of p–n or Schottky junctions, can considerably improve the efficiency of charge separation and migration. But, non-volatile elements containing ferroelectrics with narrow bandgaps and excellent photoelectric performances are still scarce. Herein, a new ferroelectric compound, BaFe4O7, has been synthesized by a conventional hydrothermal method. A polar trigonal structure (P31c) was proposed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. UV-vis-NIR diffuse reflectance spectrum revealed a visible-light bandgap Eg of 2.18 eV. Intrinsic ferroelectricity with a high Curie temperature (Tc ∼ 791 K) was confirmed by dielectric and ferroelectric measurements. The electrical saturation polarization (Ps), remanent polarization (Pr) and coercive field (Ec) were determined as 6.34 μC cm−2, 3.32 μC cm−2 and 42.38 kV cm−1 respectively. A bulk photovoltaic effect was observed in the poled sample with a steady-state photocurrent of 39 nA cm−2 and photovoltage of 0.19 V under standard AM 1.5G illumination, which demonstrated its promising applications in photoelectric devices. [ABSTRACT FROM AUTHOR]

A series of K2MnF6/KHF2 red phosphors were prepared through a low temperature way and their morphology and photoluminescence (PL) properties were investigated. The as-prepared phosphor shows an intense red emission with the strongest emission peak at 631 nm under a 454 nm excitation. Furthermore, the PL intensity and thermal stability performance, together with the quantum yields of the entitled phosphors excited under blue light are investigated and compared with relative commercial used phosphors. Finally, a bright LED with high color rendering performance of Ra = 86.8 was fabricated by using a 450 nm blue chip with YAG:Ce3+ and the as-prepared K2MnF6/KHF2 phosphor. The results indicate that the K2MnF6/KHF2 phosphors could facilitate potential application in the field of indoor lighting and backlighting. [ABSTRACT FROM AUTHOR]

Highlights: A freestanding MXene-derived defect-rich TiO2@reduced graphene oxides (M-TiO2@rGO) foam electrode was fabricated. M-TiO2@rGO presents fast Na+ storage kinetics due to capacitive contribution. M-TiO2@rGO foam electrode displays a capacity retention of 90.7% after 5000 cycles.Sodium ion batteries and capacitors have demonstrated their potential applications for next-generation low-cost energy storage devices. These devices's rate ability is determined by the fast sodium ion storage behavior in electrode materials. Herein, a defective TiO2@reduced graphene oxide (M-TiO2@rGO) self-supporting foam electrode is constructed via a facile MXene decomposition and graphene oxide self-assembling process. The employment of the MXene parent phase exhibits distinctive advantages, enabling defect engineering, nanoengineering, and fluorine-doped metal oxides. As a result, the M-TiO2@rGO electrode shows a pseudocapacitance-dominated hybrid sodium storage mechanism. The pseudocapacitance-dominated process leads to high capacity, remarkable rate ability, and superior cycling performance. Significantly, an M-TiO2@rGO//Na3V2(PO4)3 sodium full cell and an M-TiO2@rGO//HPAC sodium ion capacitor are fabricated to demonstrate the promising application of M-TiO2@rGO. The sodium ion battery presents a capacity of 177.1 mAh g−1 at 500 mA g−1 and capacity retention of 74% after 200 cycles. The sodium ion capacitor delivers a maximum energy density of 101.2 Wh kg−1 and a maximum power density of 10,103.7 W kg−1. At 1.0 A g−1, it displays an energy retention of 84.7% after 10,000 cycles. [ABSTRACT FROM AUTHOR]

Li-ion and K-ion batteries present their unique advantages of high energy density and low cost, respectively. It is a challenge to explore a universal anode with efficient electrochemical performance. Herein, a two-dimensional TiO2/reduced graphene oxide (RGO) composite was prepared by a facile hydrothermal method. TiO2 nanoparticles are transformed from Ti2C MXene and connect the RGO nanosheets to form a sheet-like structure. Serving as the anode material, the TiO2/RGO presents high capacity, remarkable rate ability and long cycling performance for both Li- and K-ion batteries. The superior electrochemical performance is attributed to the short ion diffusion path due to the small particle size (15–25 nm) and the highway for electron transport provided by RGO. In addition, RGO motivates the capacitive contribution, resulting in enhanced capacity and better rate performance. Meanwhile, the electrochemical kinetics of Li/K-ion storage was investigated by quantitative kinetics analysis. This work demonstrates a possibility to introduce the capacitive capacity to realize rapid ion storage and improve the cycling stability, providing a new strategy to design efficient electrodes for metal-ion batteries. [ABSTRACT FROM AUTHOR]

Abstract A series of single-phase Na 5 Y 4 (SiO 4) 4 F:Eu2+,Tb3+,Eu3+ phosphors were successfully synthesized by high-temperature solid state reaction and their crystal structure and luminescence properties were investigated. The chromaticity coordinates of the as-prepared phosphors under 375 nm excitation can be tuned effectively, from the light blue (0.260, 0.213) to red (0.638, 0.337) and eventually to white (0.407, 0.373) via resonant type energy transfer and appropriate choice of color combination. Furthermore, the states occupation of the dopant ions and the energy transfer mechanisms Eu2+ → Tb3+ and Tb3+ → Eu3+ have been investigated and discussed, emphasizing on spectral content and thermal stability of Na 5 Y 4 (SiO 4) 4 F:Eu2+,Tb3+,Eu3+ emission under 375 nm excitation. The results indicate that the Na 5 Y 4 (SiO 4) 4 F:Eu2+,Tb3+,Eu3+ phosphors have a potential application in UV-based White LED devices. [ABSTRACT FROM AUTHOR]

Single-phased white light emitting (Ca,Eu,Mn)9Al(PO4)7 phosphors were synthesized by conventional one-step reduction solid state reaction. The emission colors could be tuned from blue (0.170, 0.082) to white light (0.299, 0.316) and eventually to yellow (0.390, 0.400) through an efface energy transfer by controlling the dopant Eu2+/Mn2+ concentration. Energy transfer between the sensitizer Eu2+ and the activator Mn2+ has been studied and demonstrated to be a resonant type via a dipole-dipole interaction mechanism. Emissions from Eu2+ and Mn2+ in Ca9Al(PO4)7 exhibits excellent thermal stability and synchronicity. Finally, a white-LED with Ra = 79 was fabricated by using a 380 nm UV chip with single-phased (Ca0.965Eu0.005Mn0.03)Al(PO4)7 phosphor. [ABSTRACT FROM AUTHOR]