Achieving Luminescence of Sr3Ga1.98In0.02Ge4O14:0.03Cr3+ via [In3+] Substitution [Ga3+] and Its Application to NIR pc-LED in Non-Destructive Testing

Cr3+-doped Sr3Ga2Ge4O14:0.03Cr3+ (SGGO:0.03Cr3+) phosphor was synthesized via a high-temperature solid-phase method. Considering the tunable structure of SGGO, Ga3+ ions in the matrix were substituted with In3+ ions at a certain concentration. The tuned phosphor produced a red-shifted emission spectrum, with its luminescence intensity at 423 K maintained at 63% of that at room temperature; moreover, the internal quantum efficiency increased to 65.60%, and the external quantum efficiency correspondingly increased to 21.94%. On this basis, SGIGO:0.03Cr3+ was encapsulated into a pc-LED, which was applied in non-destructive testing (NDT) experiments, successfully realizing the recognition of water and anhydrous ethanol, proving its potential application in the field of NDT.

Enhanced Cycling Performance of a Li-Excess Li2CuO2 Cathode Additive by Cosubstitution Nanoarchitectonics of Ni and Mn for Lithium-Ion Batteries

The adoption of Li₂CuO₂ has drawn interest as a Li-excess cathode additive for compensating irreversible Li⁺ loss in anodes during cycling, which would move forward high-energy-density lithium-ion batteries (LIBs). Li₂CuO₂ provides a high irreversible capacity (>200 mAh g^-1) in the first cycle and an operating voltage comparable with commercial cathode materials, but its practical use is still restricted by the structural instability and spontaneous oxygen (O₂) evolution, resulting in poor overall cycling performance. It is thus crucial to reinforce the structure of Li₂CuO₂ to make it more reliable as a cathode additive for charge compensation. Pursuing the structural stability of Li₂CuO₂, herein, we demonstrate cosubstitution by heteroatoms, such as nickel (Ni) and manganese (Mn), for improving the structural stability and electrochemical performance of Li₂CuO₂. Such an approach effectively enhances the reversibility of Li₂CuO₂ by suppressing continuous structural degradation and O₂ gas evolution during cycling. Our findings provide new conceptual pathways for developing advanced cathode additives for high-energy LIBs.

Three-Dimensional Fast Na-Ion Transport in Sodium Titanate Nanoarchitectures via Engineering of Oxygen Vacancies and Bismuth Substitution

Layered sodium titanates (NTO), one of the most promising anode materials for advanced sodium-ion batteries (SIBs), feature high theoretical capacity and no serious safety concerns. The pristine NTO electrode, however, has unfavorable Na⁺ transport kinetics, due to the dominant two-dimensional (2D) Na-ion transport channels within the crystal along the low energy barrier octahedron layers, which impedes the practical application of this class of potential materials. Herein, an interesting concept of opening three-dimensional (3D) fast ion transport channels within the intrinsic NTO frameworks is proposed to enhance the electrochemical performance through a combination of oxygen vacancy generation and cation substitution strategies, by which the interlayer spacing of the NTO frameworks is expanded for fast 3D Na-ion transport. It is evidenced that the oxygen-deficient and bismuth-substituted HBNTO (Bi_xNa_2-xTi₃O_y, 0 < x < 2, 0 < y < 7, HBNTO) exhibits obvious enhancements on the reversible capacity (∼145% enhancement at 20 mAh g^-1 compared with NTO), the rate capability (∼200% enhancement at 500 mAh g^-1 compared with NTO), and the cycling stability (∼210% enhancement of retention capacity after 150 cycles at 20 mAh g^-1 compared with NTO). The molecular dynamic simulations and theoretical calculations demonstrate that the enhanced performance of HBNTO is contributed by the multiplied sodium diffusion pathways and the increased ion migration rates with the successful opening of 3D internal ion transport channels. This work demonstrates the effectiveness of the strategies in opening the 3D intercrystal ion transport channels for boosting the electrochemical performance of SIBs.

Experimental and Theoretical Study into Interface Structure and Band Alignment of the Cu2Zn1-x Cd x SnS4 Heterointerface for Photovoltaic Applications

To improve the constraints of kesterite Cu₂ZnSnS₄ (CZTS) solar cell, such as undesirable band alignment at p-n interfaces, bandgap tuning, and fast carrier recombination, cadmium (Cd) is introduced into CZTS nanocrystals forming Cu₂Zn_1-x Cd _x SnS₄ through cost-effective solution-based method without postannealing or sulfurization treatments. A synergetic experimental-theoretical approach was employed to characterize and assess the optoelectronic properties of Cu₂Zn_1-x Cd _x SnS₄ materials. Tunable direct band gap energy ranging from 1.51 to 1.03 eV with high absorption coefficient was demonstrated for the Cu₂Zn_1-x Cd _x SnS₄ nanocrystals with changing Zn/Cd ratio. Such bandgap engineering in Cu₂Zn_1-x Cd _x SnS₄ helps in effective carrier separation at interface. Ultrafast spectroscopy reveals a longer lifetime and efficient separation of photoexcited charge carriers in Cu₂CdSnS₄ (CCTS) nanocrystals compared to that of CZTS. We found that there exists a type-II staggered band alignment at the CZTS (CCTS)/CdS interface, from cyclic voltammetric (CV) measurements, corroborated by first-principles density functional theory (DFT) calculations, predicting smaller conduction band offset (CBO) at the CCTS/CdS interface as compared to the CZTS/CdS interface. These results point toward efficient separation of photoexcited carriers across the p-n junction in the ultrafast time scale and highlight a route to improve device performances.

Engineering of Electronic States on Co3 O4 Ultrathin Nanosheets by Cation Substitution and Anion Vacancies for Oxygen Evolution Reaction

Due to the earth abundance and tunable electronic properties, etc., transition metal oxides (TMOs) show attractive attention in oxygen evolution reaction. O-vacancies (V_o ) play important roles in tailoring the local surface and electronic environment to lower the activation barriers. Herein, an effective strategy is shown to enhance the oxygen evolution reduction (OER) performance on Co₃ O₄ ultrathin nanosheets via combined cation substitution and anion vacancies. The oxygen-deficient Fe-Co-O nanosheets (3-4 nm thickness) display an overpotential of 260 mV@10 mA cm^-2 and a Tafel slope of 53 mV dec^-1 , outperforming those of the benchmark RuO₂ in 1.0 m KOH. Further calculations demonstrate that the combined introduction of Fe cation and V_o with appropriate location and content finely tune the intermediate absorption, consequently lowering the rate-limiting activation energy from 0.82 to as low as 0.15 eV. The feasibility is also proved by oxygen-deficient Ni-Co-O nanosheets. This work not only establishes a clear atomic-level correlation between cation substitution, anion vacancies, and OER performance, but also provides valuable insights for the rational design of highly efficient catalysts for OER.

Synthesis and crystal structure of ABW-type SrFe1.40V0.60O4

Single crystals of SrFe1.40V0.60O4, strontium tetra-oxidodi[ferrate(III)/vanad-ate(III)], have been obtained as a side product in the course of sinter experiments aimed at the synthesis of double perovskites in the system SrO-Fe2O3-V2O5. The crystal structure can be characterized by layers of six-membered rings of TO4-tetra-hedra (T: FeIII, VIII) perpendicular to [100]. Stacking of the layers along [100] results in a three-dimensional framework enclosing tunnel-like cavities in which SrII cations are incorporated for charge compensation. The sequence of directedness of up (U) and down (D) pointing vertices of neighboring tetra-hedra in a single six-membered ring is UUUDDD. The topology of the tetra-hedral framework belongs to the zeolite-type ABW.

Osteogenic, Angiogenic, and Antibacterial Bioactive Nano-Hydroxyapatite Co-Synthesized Using γ-Polyglutamic Acid and Copper

Nano-antibacterial calcium phosphate (CaP) has attracted intense attention with regard to its wide variety of medical and biological applications. The γ-polyglutamic acid and copper cosynthesized hydroxyapatite (γ-PGA/Cu_xHAp) was synthesized using the wet method. Structural and chemical characterizations demonstrate that copper was quantitatively incorporated into the hydroxyapatite structure, and the degree of Cu substitution was up to 20 mol % in the synthesized nanocrystals. Morphology characterization showed that the size of the γ-PGA/Cu_xHAp nanoparticles decreases with the increased copper content. γ-PGA/Cu_xHAp exhibited a steady release of Cu ions. Two experimental protocols were applied to compare the antibacterial activity of the γ-PGA/Cu_xHAp samples. A positive correlation was observed between Cu content and the inhibition of bacterial growth. The study also showed that nanoparticles with smaller particle sizes exhibited higher antibacterial activities than the larger particles. Endothelial and osteoblast cells rapidly proliferated on γ-PGA/Cu_xHAp, whereas high concentrations (20 mol %) of Cu ions reduced cell proliferation. In the rat calvarial defect model, some γ-PGA/Cu_xHAp samples such as γ-PGA/Cu_xHAp (x = 8, 16) showed efficient bone regeneration capacities at 12 weeks post implantation. Thus, the multibiofunctional γ-PGA/Cu_xHAp nanocomposite exhibited degradative, angiogenic, bactericidal and bone regenerative properties, providing a potential means to address some of the critical challenges in the field of bone tissue engineering.

Acetamidinium-Substituted Methylammonium Lead Iodide Perovskite Solar Cells with Higher Open-Circuit Voltage and Improved Intrinsic Stability

We report acetamidinium (AA)-substituted methylammonium (MA) lead iodide perovskite solar cells. AA has a restricted C-N bond rotation because of delocalized π-electron cloud over the N-C-N bond and the presence of an additional N-H···I bond (4H-bond in AA as compared to 3H-bond in MA). These bonding structures strengthen the electrostatic interaction and stabilize the AA cation inside the perovskite matrix. AA, a larger cation, is substitutional only up to 10%. Devices made with 10% AA-substituted films show an average V_oc of 1.12 V, higher than the average V_oc of 1.04 V in the case of MA lead halide perovskite (MAPbI₃). This increase in V_oc can be attributed to an increase in carrier lifetime from 20 μs in the case of MAPbI₃ to 32 μs for 10% AA-substituted films respectively. Devices with 18.29% champion and 16.3% average efficiency were fabricated for films with 10% AA. Degradation experiments confirm that the material stability also makes devices more stable; under ambient exposure (72 ± 3% RH), devices with 10% AA retain 70% of their initial power conversion efficiencies (PCEs) up to 480 h. Under the same conditions, the PCEs of reference MAPbI₃ devices reduced to 43% of their initial value in 480 h.

Improving Carrier-Transport Properties of CZTS by Mg Incorporation with Spray Pyrolysis

High nonradiative recombination, low diffusion length and band tailing are often associated with a large open circuit voltage deficit, which results in low efficiency of Cu₂ZnSnS₄ (CZTS) solar cells. Recently, cation substitution in CZTS has gained interest as a plausible solution to suppress these issues. However, the common substitutes, Ag and Cd, are not ideal due to their scarcity and toxicity. Other transition-metal candidates (e.g., Mn, Fe, Co, or Ni) are multivalent, which may form harmful deep-level defects. Magnesium, as one of the viable substitutes, does not have these issues, as it is very stable in +2 oxidation state, abundant, and nontoxic. In this study, we investigate the effect of Mg incorporation in sulfur-based Cu₂ZnSnS₄ to form Cu₂Mg_xZn_1-xSnS₄ by varying x from 0.0 to 1.0. These films were fabricated by chemical spray pyrolysis and the subsequent sulfurization process. At a high Mg content, it is found that Mg does not replace Zn to form a quaternary compound, which leads to the appearance of the secondary phases in the sample. However, a low Mg content (Cu₂Mg_0.05Zn_0.95SnS₄) improves the power conversion efficiency from 5.10% (CZTS) to 6.73%. The improvement is correlated to the better carrier-transport properties, as shown by a lesser amount of the ZnS secondary phase, higher carrier mobility, and shallower acceptor defects level. In addition, the Cu₂Mg_0.05Zn_0.95SnS₄ device also shows better charge-collection property based on the higher fill factor and quantum efficiency despite having lower depletion width. Therefore, we believe that the addition of a small amount of Mg is another viable route to improve the performance of the CZTS solar cell.

Comprehensive Review of P2-Type Na2/3Ni1/3Mn2/3O2, a Potential Cathode for Practical Application of Na-Ion Batteries

P2-type Na_2/3Ni_1/3Mn_2/3O₂ is a promising cathode material for practical applications in Na-ion batteries, due to its high energy density, high volumetric capacity, excellent Na ion conductivity, ease of synthesis, and good stability in air. Yet, it is subject to structural rearrangements on charging to high voltage/low Na content and Na⁺/vacancy ordering transitions, which lead to poor reversibility and dramatic capacity decay upon cycling. In this Review, we present the latest advances related to Na_2/3Ni_1/3Mn_2/3O₂, with a main focus on strategies to stabilize the structural framework and improve the electrochemical properties. Practical issues and challenges are also proposed on the basis of current research status and progress.

Color-Tunable Phosphor [Mg1.25Si1.25Al2.5]O3N3:Eu2+-A New Modified Polymorph of AlON with Double Sites Related Luminescence and Low Thermal Quenching

Aluminum oxynitride (AlON) was commonly used in functional ceramic materials, including phosphors for white light-emitting diodes (LEDs). In the current work, a new polymorph of AlON structure, single phase [Mg_1.25Si_1.25Al_2.5]O₃N₃, has been devised and synthesized through the solid-state reaction at a rather low temperature of 1550 °C. Its structure has been calculated by the Rietveld refinement. The [Mg_1.25Si_1.25Al_2.5]O₃N₃ crystallizes in trigonal with lattice parameters of a = b = 3.0312 Å, c = 41.5758 Å, V = 330.83 ų, respectively, and it is formed by Mg²⁺ and Si⁴⁺ ions replacing partical Al³⁺ ions of Al₅O₃N₃. The photoluminescence spectra of a series of Eu²⁺ doped [Mg_1.25Si_1.25Al_2.5]O₃N₃ show a tunable light ranging from cyan to orange with a full-spectrum-covered emission and a wide excitation band with two peaks located at 290 and 335 nm. This is resulted from the two possible sites offered by the cation substitution for Eu²⁺ to occupy and thus broadening the emission spectra, which significantly enrich the monotonous luminescent properties of conventional AlON phosphors. Additionally, the energy transfer from one site to another has been identified using the decay curves and time-resolved emission spectra. The scanning electron microscopy and transmission electron microscopy characterization confirmed the sample's great crystallinity and the thermal stability with more than 85% of the initial intensity at 250 °C further indicates its potential in white LED applications.

Cationic Substitutions in Hydroxyapatite: Current Status of the Derived Biofunctional Effects and Their In Vitro Interrogation Methods

High-performance bioceramics are required for preventing failure and prolonging the life-time of bone grafting scaffolds and osseous implants. The proper identification and development of materials with extended functionalities addressing socio-economic needs and health problems constitute important and critical steps at the heart of clinical research. Recent findings in the realm of ion-substituted hydroxyapatite (HA) could pave the road towards significant developments in biomedicine, with an emphasis on a new generation of orthopaedic and dentistry applications, since such bioceramics are able to mimic the structural, compositional and mechanical properties of the bone mineral phase. In fact, the fascinating ability of the HA crystalline lattice to allow for the substitution of calcium ions with a plethora of cationic species has been widely explored in the recent period, with consequent modifications of its physical and chemical features, as well as its functional mechanical and in vitro and in vivo biological performance. A comprehensive inventory of the progresses achieved so far is both opportune and of paramount importance, in order to not only gather and summarize information, but to also allow fellow researchers to compare with ease and filter the best solutions for the cation substitution of HA-based materials and enable the development of multi-functional biomedical designs. The review surveys preparation and synthesis methods, pinpoints all the explored cation dopants, and discloses the full application range of substituted HA. Special attention is dedicated to the antimicrobial efficiency spectrum and cytotoxic trade-off concentration values for various cell lines, highlighting new prophylactic routes for the prevention of implant failure. Importantly, the current in vitro biological tests (widely employed to unveil the biological performance of HA-based materials), and their ability to mimic the in vivo biological interactions, are also critically assessed. Future perspectives are discussed, and a series of recommendations are underlined.

4/2018)

Low‐cost and environmentally friendly kesterite structural Cu₂ZnSn(S,Se)₄ (CZTSSe) thin‐film solar cells have experienced a significant increase in power conversion efficiency from about 5% to a record of 12.6%. To further improve device performance, various cation substitution technologies have been proposed to modify the electronic and optical properties of the kesterite light absorber layer. In article https://doi.org/10.1002/advs.201700744, Yi Zhang and co‐workers review recent cutting‐edge research focusing on various cation substitution methods.

Cation Substitution in Earth-Abundant Kesterite Photovoltaic Materials

As a promising candidate for low-cost and environmentally friendly thin-film photovoltaics, the emerging kesterite-based Cu2ZnSn(S,Se)4 (CZTSSe) solar cells have experienced rapid advances over the past decade. However, the record efficiency of CZTSSe solar cells (12.6%) is still significantly lower than those of its predecessors Cu(In,Ga)Se2 (CIGS) and CdTe thin-film solar cells. This record has remained for several years. The main obstacle for this stagnation is unanimously attributed to the large open-circuit voltage (VOC) deficit. In addition to cation disordering and the associated band tailing, unpassivated interface defects and undesirable energy band alignment are two other culprits that account for the large VOC deficit in kesterite solar cells. To capture the great potential of kesterite solar cells as prospective earth-abundant photovoltaic technology, current research focuses on cation substitution for CZTSSe-based materials. The aim here is to examine recent efforts to overcome the VOC limit of kesterite solar cells by cation substitution and to further illuminate several emerging prospective strategies, including: i) suppressing the cation disordering by distant isoelectronic cation substitution, ii) optimizing the junction band alignment and constructing a graded bandgap in absorber, and iii) engineering the interface defects and enhancing the junction band bending.

Luminescence enhancement of (Sr1-x Mx )2 SiO4 :Eu2+ phosphors with M (Ca2+ /Zn2+ ) partial substitution for white light-emitting diodes

Eu²⁺ -doped Sr₂ SiO₄ phosphor with Ca²⁺ /Zn²⁺ substitution, (Sr_1-x M_x )₂ SiO₄ :Eu²⁺ (M = Ca, Zn), was prepared using a high-temperature solid-state reaction method. The structure and luminescence properties of Ca²⁺ /Zn²⁺ partially substituted Sr₂ SiO₄ :Eu²⁺ phosphors were investigated in detail. With Ca²⁺ or Zn²⁺ added to the silicate host, the crystal phase could be transformed between the α-form and the β-form of the Sr₂ SiO₄ structure. Under UV excitation at 367 nm, all samples exhibit a broad band emission from 420 to 680 nm due to the 4f⁶ 5d¹  → 4f⁷ transition of Eu²⁺ ions. The broad emission band consists of two peaks at 482 and 547 nm, which correspond to Eu²⁺ ions occupying the ten-fold oxygen-coordinated Sr.(I) site and the nine-fold oxygen-coordinated Sr.(II) site, respectively. The luminescence properties, including the intensity and lifetime of Sr₂ SiO₄ :Eu²⁺ phosphors, improved remarkably on Ca²⁺ /Zn²⁺ addition, and promote its application in white light-emitting diodes. Copyright © 2016 John Wiley & Sons, Ltd.

A Crucial Role of Rh Substituent Ion in Photoinduced Internal Electron Transfer and Enhanced Photocatalytic Activity of CdS-Ti(5.2-x)/6 Rhx /2 O2 Nanohybrids

The photocatalytic activity and photostability of CdS quantum dot (QD) can be remarkably enhanced by hybridization with Rh-substituted layered titanate nanosheet even at very low Rh substitution rate (<1%). Mesoporous CdS-Ti(5.2-x)/6 Rhx/2O2 nanohybrids are synthesized by a self-assembly of exfoliated Ti(5.2-x)/6 Rhx/2O2 nanosheets with CdS QDs. The partial substitution of Rh(3+)/Rh(4+) ions for Ti(4+) ions in layered titanate is quite effective in enhancing an electronic coupling between hybridized CdS and titanate components via the formation of interband Rh 4d states. A crucial role of Rh substituent ion in the internal electron transfer is obviously evidenced from in situ X-ray absorption spectroscopy showing the elongation of (RhO) bond under visible light irradiation. This is the first spectroscopic evidence for the important role of substituent ion in the photoinduced electron transfer of hybrid-type photocatalyst. The CdS-Ti(5.2-x)/6 Rhx/2O2 nanohybrids show much higher photocatalytic activity for H2 production and better photostability than do CdS and unsubstituted CdS-TiO2 nanohybrid. This result is ascribable to the enhancement of visible light absorptivity, the depression of electron-hole recombination, and the enhanced hole curing of CdS upon Rh substitution. The present study underscores that the hybridization with composition-controlled inorganic nanosheet provides a novel efficient methodology to optimize the photo-related functionalities of semiconductor nanocrystal.