A3A'3Zn6Te4O24 (A = Na, A' = Rare Earth) Garnets: A-Site Ordered Noncentrosymmetric Structure, Photoluminescence, and Na-Ion Conductivity.

A large number of oxides that adopt the centrosymmetric (CS) garnet-type structure (space group Ia3̅d) have been widely studied as promising magnetic and host materials. Hitherto, no noncentrosymmetric (NCS) garnet has been reported yet, and a strategy to NCS garnet design is therefore significant for expanding the application scope. Herein, for the series A3A'3Zn6Te4O24 (A = Na, A' = La, Eu, Nd, Y, and Lu), we demonstrated that the structural symmetry evolution from CS Ia3̅d (A' = La) to NCS I4122 (A' = Eu, Nd, Y, and Lu) could be achieved due to the A-site cationic ordering-driven inversion symmetry breaking. Na3A'3Zn6Te4O24 (A' = rare earth) are the first garnets that possess NCS structures with A-site cationic ordering. Diffuse reflectance spectra and theoretic calculations demonstrated that all these NCS garnets are indirect semiconductors. Moreover, their potential applications as host materials for red phosphors and Na-ion conductors were also investigated in detail, which firmly confirmed the NCS structure and A-site cationic ordering. Our findings have paved the way to design NCS or even polar garnets that show intriguing functional properties, such as ferroelectricity, multiferroicity, and second harmonic generation.

Structural Diversity and Incompatibility Induced Complex Phase Formation Behavior in the Stuffed Tridymites Ca1-xSrxGa2O4.

Stuffed tridymites AM2O4 composed of a condensed MO4-tetrahedra-based framework have been widely investigated due to their structural diversity and rich physical properties. Herein, the strategy of stuffing mixed Ca2+ and Sr2+ cations into the [Ga2O4]2- framework in (Ca1-xSrx)Ga2O4 (CSGO, 0 ≤ x ≤ 1) is utilized to manipulate the phase formation behavior with different structure types at particular annealing temperatures. Five derivatives, including α- and ß-CaGa2O4, ß- and γ-SrGa2O4, and new CSGO-type structures, were observed. The distinctive feature of the CSGO-structure is the coexistence of UUDDUD- and UDUDUD-type six-membered rings, where U (up) and D (down) denote the orientations of GaO4-tetrahedra with respect to the plane grids, in a ratio of 2:1. Single-phase α-Ca1-xSrxGa2O4 (x < 0.2) and γ-Ca1-xSrxGa2O4 (x > 0.67) could be obtained at low temperatures. Biphasic regions, including α-Ca1-xSrxGa2O4/CSGO (0.2 ≤ x ≤ 0.67), γ-Ca1-xSrxGa2O4/CSGO (0.67 < x ≤ 0.8), and ß-Ca1-xSrxGa2O4/CSGO (0.8 < x < 1), were observed at the intermediate temperature region and evolve irreversibly into the CSGO single-phase region upon elevating the temperature. Moreover, the structure-property relationship of the new CSGO-phase was further studied by doping coordination-sensitive Bi3+ activators to advance the development and applications of stuffed tridymites.

Two-dimensional hollow carbon skeleton decorated with ultrafine Co3O4 nanoparticles for enhanced lithium storage.

Transition metal oxides have shown high theoretical capacities as anode materials and have been considered as high potential materials to substitute graphite for composing new generations of lithium-ion batteries (LIBs). However, the considerable volume changes of transition metal oxide materials during practical processes have limited their applications. Herein, we report a simple approach to construct a two-dimensional (2D) hollow carbon skeleton decorated with ultrafine Co3O4 nanoparticles (Co3O4/C). This composite is derived from a leaf-like zeolitic imidazolate framework-L (ZIF-L (Co)) via etching coordination using tannic acid (TA). The Co3O4/C has a unique structure consisting of 2D carbon skeleton, ultrafine Co3O4 nanoparticle, and open channel, which can accelerate electron transport, alleviate volume change, and facilitate ion diffusion. Benefiting from these features, the LIBs assembled using Co3O4/C as anode material exhibits superior reversible cycle performance and impressive rate property. This study provides an efficient strategy for implementing transition metal oxide-based composites for energy storage applications.

Preparation and electrical properties of inorganic electride [Y2Ti2O6]2+(2e-).

Oxygen-depleted samples [Y2Ti2O7-x ]2x+(2xe-) (0 ≤ x ≤ 1.0) were prepared by reducing Y2TiO7 powders at 500 °C to 650 °C using CaH2 as a reductive agent, where x represents the content of , which was determined by thermogravimetric analysis. Powder X-ray diffraction patterns illustrate that the pure pyrochlore phase is kept for the samples with x ≤ 1.0, whereas the apparent x values surpass 1.0, and the impurity phase Y2O3 appears. The electride [Y2Ti2O7-x ]2x+(2xe-) (x ≈ 1.0) can be obtained under a reductive condition, in which the concentration of VO is 7.75 × 1021 cm-3. The electron paramagnetic resonance measurements gave the concentration of unpaired electrons in the electride as 1.30 × 1021 cm-3, indicating that the degree of the ionization of is less than 10%. Conductivity measurements for a sintered pellet sample (relative density ∼ 70%) indicate that the electride has quite high conductivity (∼1.09 S cm-1 at 300 K). The conduction was interpreted by using the variable range hopping mechanisms.

Narrow-band red emitting oxonitridosilicate phosphor La4-xSr2+xSi5N12-xOx:Pr3+ (x≈ 1.69).

The new oxonitridosilicates Ln4-xSr2+xSi5N12-xOx (Ln = La, Ce) were synthesized by high temperature solid-state reactions. The crystal structures were solved and refined from both single-crystal and powder X-ray diffraction data. These oxonitridosilicate compounds crystallize in the monoclinic space group P21/n (no. 14) and exhibit a double-layer structure made up of corner-sharing Si(O/N)4 tetrahedra. When excited with near-UV and blue light, the Pr3+ doped La2.31Sr3.69Si5N10.31O1.69 phosphor shows a narrow-band red emission peaking at 625 nm with a full width at half-maximum of 40 nm.

A color tunable and white light emitting Ca2Si5N8:Ce3+,Eu2+ phosphor via efficient energy transfer for near-UV white LEDs.

Achieving tunable color and white light emission in a single phase phosphor is a challenging issue. Here, a series of Ce3+-Eu2+ co-doped Ca2Si5N8 phosphors were successfully synthesized by a high temperature solid state method. Luminescence properties, energy transfer (ET) and thermal quenching of the as-synthesized samples were investigated in detail. The emission color of as-prepared Ca1.94Na0.03Si5N8:0.03Ce3+,yEu2+ (0.0000 ≤ y ≤ 0.0035) could be tuned from blue to white light and eventually to orange via ET by changing the Ce3+/Eu2+ ratio. ET efficiency from Ce3+ to Eu2+ could reach up to 68.0% and the ET mechanism was demonstrated to be a non-radiative dipole-dipole interaction. More importantly, when y = 0.0012, approximate standard white light was generated with CIE coordinates of (0.335, 0.341). A photoluminescence (PL) mechanism was proposed to understand PL properties and thermal properties of the as-prepared phosphors. Additionally, the achieved white light phosphor Ca1.9388Na0.03Si5N8:0.03Ce3+,0.0012Eu2+ had good thermal stability, exhibiting about 75% at 150 °C and 64% at 200 °C of the emission intensity at 25 °C, respectively. The chromaticity shifts of Ca1.9388Na0.03Si5N8:0.03Ce3+,0.0012Eu2+ were 0.0032 at 150 °C and 0.0152 at 200 °C, respectively, which were only 27% and 42% of the commercial white-emitting phosphor mixture at the corresponding temperature. Furthermore, a proof-of-concept white LED was fabricated by combining the single component phosphor Ca1.9388Na0.03Si5N8:0.03Ce3+,0.0012Eu2+ with a near UV LED chip. All results demonstrate the promising application of the Ca2Si5N8:Ce3+,Eu2+ single phosphor for near-UV white LEDs.

Narrow-band blue emitting nitridomagnesosilicate phosphor Sr8Mg7Si9N22:Eu2+ for phosphor-converted LEDs.

We report a novel narrow-band blue emitting phosphor Sr7.92Mg7Si9N22:0.08Eu2+. The crystal structure of Sr8Mg7Si9N22 is composed of corner-sharing and edge-sharing [SiN4] tetrahedra and distorted square-pyramid [MgN5] polyhedra. Under 350 nm excitation, Eu2+ doped Sr8Mg7Si9N22 emits narrow-band blue light with maximum intensity at 450 nm and a fwhm of 38 nm.