Studies of Terbium Bridge: Saturation Phenomenon, Significance of Sensitizer and Mechanisms of Energy Transfer, and Luminescence Quenching

Terbium chain in the form of S → (Tb³⁺)_<i>n</i> → A (S = Ce³⁺ or Eu²⁺, A = Eu³⁺), as a promising energy transfer (ET) approach, has been proposed to enhance Eu³⁺ emission for solid-state lighting. However, the viewpoint of ET from S to A via the terbium chain (Tb³⁺–Tb³⁺–Tb³⁺–...) is very doubtful. Here, hosts of Ba₃Ln­(PO₄)₃, LnPO₄, LnBO₃, and Na₂Ln₂B₂O₇ doped with Ce³⁺ → (Tb³⁺)_<i>n</i> → Eu³⁺ or (Tb³⁺)_<i>n</i> → Eu³⁺ are synthesized to prove the universality of S → (Tb³⁺)_<i>n</i> → A in inorganic hosts and to study the unsolved issues. Saturation distance of Tb³⁺–Eu³⁺, estimated with the empirical data of different hosts, is proposed to be a criterion for determining whether a spectral chromaticity coordinate keeps constant. A branch model is put forward to replace the chain model to explain the role of (Tb³⁺)_<i>n</i> in ET from Ce³⁺ to Eu³⁺ and the necessity of high content of Tb³⁺; the term “terbium bridge” is used to replace “terbium chain”, and the value of <i>n</i> is determined to be two or three. The intensity quenching of Eu³⁺ emission is attributed to the surface defects ascribed to the smaller particles and larger specific surface area rather than the concentration quenching of Tb³⁺. Based on the saturation distance and the mechanism of luminescence quenching, the necessary concentration of Tb³⁺ for (Tb³⁺)_<i>n</i> can be estimated as long as the cell parameters are already known and the luminescent efficiency of Eu³⁺ can be further improved by optimizing the synthesis method to decrease the quantity of surface defects

A Facile Activation Strategy for an MOF-Derived Metal-Free Oxygen Reduction Reaction Catalyst: Direct Access to Optimized Pore Structure and Nitrogen Species

Rational design of the microstructure and intrinsic active sites of nitrogen-doped carbon (NC) materials to achieve highly efficient oxygen reduction reaction (ORR) electrocatalysts is extremely important for many renewable energy devices. Herein, we develop a metal–organic framework (MOF) derived metal-free NC material via a simple and low-cost NH₃ activation strategy. With NH₃ activation, the ORR catalytic performance of the MOF-derived material shows a great promotion. The material outperforms commercial Pt/C catalyst toward ORR catalysis in alkaline media with ∼28 mV higher half-wave potential. This amazing ORR performance might be attributed to its large specific surface area, hierarchical porosity, and full exposure of valid N species (mainly graphitic-N) to the ORR, which result from the facile NH₃ activation

Highly Thermally Stable Single-Component White-Emitting Silicate Glass for Organic-Resin-Free White-Light-Emitting Diodes

Thermal management is still a great challenge for high-power phosphor-converted white-light-emitting diodes (pc-WLEDs) intended for future general lighting. In this paper, a series of single-component white-emitting silicate SiO₂–Li₂O–SrO–Al₂O₃–K₂O–P₂O₅: Ce³⁺, Tb³⁺, Mn²⁺ (SLSAKP: Ce³⁺, Tb³⁺, Mn²⁺) glasses that simultaneously play key roles as a luminescent convertor and an encapsulating material for WLEDs were prepared via the conventional melt-quenching method, and systematically studied using their absorption spectra, transmittance spectra, photoluminescence excitation and emission spectra in the temperature range 296–498 K, decay curves, and quantum efficiency. The glasses show strong and broad absorption in 250–380 nm region and exhibit intense white emission, produced by in situ mixing of blue-violet, green, and orange-red light from Ce³⁺, Tb³⁺, and Mn²⁺ ions, respectively, in a single glass component. The quantum efficiency of SLSAKP: 0.3%Ce³⁺, 2.0%Tb³⁺, 2.0%Mn²⁺ glass is determined to be 19%. More importantly, this glass shows good thermal stability, exhibiting at 373 and 423 K about 84.56 and 71.02%, respectively, of the observed room temperature (298 K) emission intensity. The chromaticity shift of SLSAKP: 0.3%Ce³⁺, 2.0%Tb³⁺, 2.0%Mn²⁺ is 2.94 × 10^–2 at 498 K, only 57% of the commercial triple-color white-emitting phosphor mixture. Additionally, this glass shows no transmittance loss at the 370 nm emission of a UV-Chip-On-Board (UV-COB) after thermal aging for 240 h, compared with the 82% transmittance loss of epoxy resin. The thermal conductivity of the glass is about 1.07 W/mK, much larger than the 0.17 W/mK of epoxy resin. An organic-resin-free WLEDs device based on SLSAKP: 0.3%Ce³⁺, 2.0%Tb³⁺, 2.0%Mn²⁺ glass and UV-COB is successfully demonstrated. All of our results demonstrate that the presented Ce³⁺/Tb³⁺/Mn²⁺ tridoped lithium–strontium–silicate glass may serve as a promising candidate for high-power WLEDs

Chestnut-Like TiO₂@α-Fe₂O₃ Core–Shell Nanostructures with Abundant Interfaces for Efficient and Ultralong Life Lithium-Ion Storage

Transition metal oxides caused much attention owing to the scientific interests and potential applications in energy storage systems. In this study, a free-standing three-dimensional (3D) chestnut-like TiO₂@α-Fe₂O₃ core–shell nanostructure (TFN) is rationally synthesized and utilized as a carbon-free electrode for lithium-ion batteries (LIBs). Two new interfaces between anatase TiO₂ and α-Fe₂O₃ are observed and supposed to provide synergistic effect. The TiO₂ microsphere framework significantly improves the mechanical stability, while the α-Fe₂O₃ provides large capacity. The abundant boundary structures offer the possibility for interfacial lithium storage and electron transport. The as-prepared TFN delivers a high capacity of 820 mAh g^–1 even after 1000 continuous cycles with a Coulombic efficiency of ca. 99% at a current of 500 mA g^–1, which is better than the works reported previously. A thin gel-like SEI (solid electrolyte interphase) film and Fe⁰ phase yielded during charge/discharge cycling have been confirmed which makes it possible to alleviate the volumetric change and enhance the electronic conductivity. This confirmation is helpful for understanding the mechanism of lithium-ion storage in α-Fe₂O₃-based materials. The as-prepared free-standing TFN with excellent stability and high capacity can be an appropriate candidate for carbon-free anode material in LIBs

Tunable Luminescent Properties and Concentration-Dependent, Site-Preferable Distribution of Eu²⁺ Ions in Silicate Glass for White LEDs Applications

The design of luminescent materials with widely and continuously tunable excitation and emission is still a challenge in the field of advanced optical applications. In this paper, we reported a Eu²⁺-doped SiO₂-Li₂O-SrO-Al₂O₃-K₂O-P₂O₅ (abbreviated as SLSAKP:Eu²⁺) silicate luminescent glass. Interestingly, it can give an intense tunable emission from cyan (474 nm) to yellowish-green (538 nm) simply by changing excitation wavelength and adjusting the concentration of Eu²⁺ ions. The absorption spectra, photoluminescence excitation (PLE) and emission (PL) spectra, and decay curves reveal that there are rich and distinguishable local cation sites in SLSAKP glasses and that Eu²⁺ ions show preferable site distribution at different concentrations, which offer the possibility to engineer the local site environment available for Eu²⁺ ions. Luminescent glasses based color and white LED devices were successfully fabricated by combining the as-synthesized glass and a 385 nm n-UV LED or 450 nm blue LED chip, which demonstrates the potential application of the site engineering of luminescent glasses in advanced solid-state lighting in the future

Assessment of the role of an ABCC transporter TuMRP1 in the toxicity of abamectin to Tetranychus urticae

The rapid evolution of pest resistance threatens the sustainable utilization of bioinsecticides such as abamectin, and so deciphering the molecular mechanisms affecting toxicity and resistance is essential for their long-term application. Historical studies of abamectin resistance in arthropods have mainly focused on mechanisms involving the glutamate-gated chloride channel (GluCl) targets, with the role of metabolic processes less clear. The two-spotted spider mite, Tetranychus urticae, is a generalist herbivore notorious for rapidly developing resistance to pesticides worldwide, and abamectin has been widely used for its control in the field. After reanalyzing previous transcriptome and RNA-seq data, we here identified an ABC transporter subfamily C gene in T. urticae named multidrug resistance-associated protein 1 (TuMRP1), whose expression differed between susceptible and resistant populations. Synergism bioassays with the inhibitor MK-571, the existence of a genetic association between TuMRP1 expression and susceptibility to abamectin, and the effect of RNA interference mediated silencing of TuMRP1 were all consistent with a direct role of this transporter protein in the toxicity of abamectin. Although ABC transporters are often involved in removing insecticidal compounds from cells, our data suggest either an alternative role for these proteins in the mechanism of action of abamectin or highlight an indirect association between their expression and abamectin toxicity

Topotactic Growth, Selective Adsorption, and Adsorption-Driven Photocatalysis of Protonated Layered Titanate Nanosheets

Layered titanates with selective adsorption ability and adsorption-driven photocatalytic property can be quite attractive due to their potential applications in water purification. In this work, lepidocrocite-like layered protonated titanate (H₂Ti₂O₅·H₂O, denoted as HTO) nanosheets were successfully synthesized by an ion-exchange process. It turns out that this layered structure displays an abundant and selective adsorption toward the fluoroquinolone pharmaceutical compared with some large dye molecules due to a size selectivity of the interlayer spacing of HTO and the molecular horizontal size, as well as their electrostatic interaction. The uptake ability of HTO could be readily controlled through adjusting the pH values of adsorbate solution, and the maximum uptake capacity was achieved at the pH value of about 5.5 for ciprofloxacin (CIP) and 6.5 for moxifloxacin (MOX). The adsorption amount of smaller nalidixic acid (NAL) showed an increasing tendency as the pH value decreased. Moreover, the two-dimensional layered crystal structure also permits such HTO nanosheets to have a large percentage of (010) faces exposed, which is considerably provided by the interlayer surfaces of these nanosheets. The (010) surface has a similar Ti and O atomic arrangement as to the highly reactive anatase TiO₂(001) one. Due to these specific characteristics, these HTO nanosheets show excellent photocatalytic activity in degrading CIP under UV light irradiation as well as possess a superior adsorption ability to remove CIP from aqueous solution selectively and efficiently. The photocatalytic reaction is believed to be mainly conducted on the active anatase (001)-like interlayer (010) surfaces of the layered structures since the as-prepared HTO performs an adsorption-driven molecular recognitive photocatalytic reaction

Localization of Oxygen Interstitials in CeSrGa₃O_7+δ Melilite

The solubility of Ce in the La_1–<i>x</i>Ce_<i>x</i>SrGa₃O_7+δ and La_{1.54–<i>x</i>}Ce_<i>x</i>Sr_0.46Ga₃O_7.27+δ melilites was investigated, along with the thermal redox stability in air of these melilites and the conductivity variation associated with oxidization of Ce³⁺ into Ce⁴⁺. Under CO reducing atmosphere, the La in LaSrGa₃O₇ may be completely substituted by Ce to form the La_1–<i>x</i>Ce_<i>x</i>SrGa₃O_7+δ solid solution, which is stable in air to ∼600 °C when <i>x</i> ≥ 0.6. On the other side, the La_{1.54–<i>x</i>}Ce_<i>x</i>Sr_0.46Ga₃O_7.27+δ compositions displayed much lower Ce solubility (<i>x</i> ≤ 0.1), irrespective of the synthesis atmosphere. In the as-made La_1–<i>x</i>Ce_<i>x</i>SrGa₃O_7+δ, the conductivity increased with the cerium content, due to the enhanced electronic conduction arising from the 4f electrons in Ce³⁺ cations. At 600 °C, CeSrGa₃O_7+δ showed a conductivity of ∼10^–4 S/cm in air, nearly 4 orders of magnitude higher than that of LaSrGa₃O₇. The oxidation of Ce³⁺ into Ce⁴⁺ in CeSrGa₃O_7+δ slightly reduced the conductivity, and the oxygen excess did not result in apparent increase of oxide ion conduction in CeSrGa₃O_7+δ. The Ce doping in air also reduced the interstitial oxide ion conductivity of La_1.54Sr_0.46Ga₃O_7.27. Neutron powder diffraction study on CeSrGa₃O_7.39 composition revealed that the extra oxygen is incorporated in the four-linked GaO₄ polyhedral environment, leading to distorted GaO₅ trigonal bipyramid. The stabilization and low mobility of interstitial oxygen atoms in CeSrGa₃O_7+δ, in contrast with those in La_1+<i>x</i>Sr_1–<i>x</i>Ga₃O_{7+0.5<i>x</i>}, may be correlated with the cationic size contraction from the oxidation of Ce³⁺ to Ce⁴⁺. These results provide a new comprehensive understanding of the accommodation and conduction mechanism of the oxygen interstitials in the melilite structure

Multiple Nucleation and Crystal Growth of Barium Titanate

Crystal growth of cubic BaTiO₃ in the presence of polyethylene glycol-200 (PEG-200) is investigated step by step using powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Titanium precursor Ti­(OC₄H₉)₄ aggregates with PEG to form spherical colloidal particles at the very beginning. Multiple nucleation of BaTiO₃ takes place on the surface of these colloidal particles. The nanocrystallites then self-adjust their orientations likely under dipole–dipole interaction and/or intercrystallite interactions enhanced by surface adsorbed polymers, followed by an orientated connection and crystal extension via an Ostwald ripening process. The final BaTiO₃ crystals have a novel dodecahedral morphology. The formation mechanism is proposed to be attributed to the selective adsorption of PEG molecules on the {110} crystal planes, significantly reducing the crystal growth rate on these surfaces. A kinetic model is proposed based on the calculated crystallite sizes using the Scherrer equation. The physical meaning of the model and a significant fake reduction of the crystallite size is discussed

Solid-State ²⁹Si NMR and Neutron-Diffraction Studies of Sr_0.7K_0.3SiO_2.85 Oxide Ion Conductors

K/Na-doped SrSiO₃-based oxide ion conductors were recently reported as promising candidates for low-temperature solid-oxide fuel cells. Sr_0.7K_0.3SiO_2.85, close to the solid-solution limit of Sr_1–<i>x</i>K_<i>x</i>SiO_{3–0.5<i>x</i>}, was characterized by solid-state ²⁹Si NMR spectroscopy and neutron powder diffraction (NPD). Differing with the average structure containing the vacancies stabilized within the isolated Si₃O₉ tetrahedral rings derived from the NPD study, the ²⁹Si NMR data provides new insight into the local defect structure in Sr_0.7K_0.3SiO_2.85. The Q¹-linked tetrahedral Si signal in the ²⁹Si NMR data suggests that the Si₃O₉ tetrahedral rings in the K-doped SrSiO₃ materials were broken, forming Si₃O₈ chains. The Si₃O₈ chains can be stabilized by either bonding with the oxygen atoms of the absorbed lattice water molecules, leading to the Q¹-linked tetrahedral Si, or sharing oxygen atoms with neighboring Si₃O₉ units, which is consistent with the Q³-linked tetrahedral Si signal detected in the ²⁹Si NMR spectra