High-temperature Route Research Articles

Bright red luminescence from Mn4+ ions doped Sr2LuTaO6 double-perovskite phosphors

This paper reported on the synthesis, crystal structure and photoluminescence properties of novel deep-red emitting Mn4+ ions doped Sr2LuTaO6 (SLT) double-perovskite phosphors. The SLT:Mn4+ red phosphors were successfully synthesized by high-temperature solid-state route under air atmosphere. The phase purity and crystal structure of these as-prepared SLT:Mn4+ red phosphors were analyzed by X-ray diffraction (XRD) patterns and XRD Rietveld refinement. The luminescence properties including excitation and emission spectra, luminescence decay lifetimes, the Commission International De IʼEclairage (CIE) chromaticity coordinates, temperature-dependent photoluminescence spectra, and internal quantum efficiency were investigated in detail. It was found that under 346 nm excitation, the SLT:Mn4+ phosphors exhibited bright red emissions around 686 nm in the 630–750 nm wavelength range. Besides, Mn4+ concentration dependent luminescence properties were also analyzed, and the optimal doping concentration of Mn4+ ions was found to be 0.4%. More importantly, the CIE chromaticity coordinates of SLT:0.4%Mn4+ sample were determined to be (0.7286, 0.2714), and its internal quantum efficiency was measured as 37%.

Manifestation of dissimilar types of magnetism in iron- and chromium-substituted Mn2SnS4.

Mn2SnS4 belongs to the MII2AIVQ4 (M = transition metal; A = Si, Ge and Sn; Q = S, Se and Te) class of compounds that crystallizes in the orthorhombic space group Cmmm and shows complex magnetic properties. Here we report the synthesis and magnetic properties of Fe- and Cr-substituted Mn2SnS4 quaternary chalcogenides. All these compounds have been synthesized using a high-temperature solid-state route. Room temperature neutron diffraction studies on the specific compositions of chromium- and iron-substituted compounds were performed to obtain the site occupancy of different elements in the unit cell. The neutron diffraction analysis by employing the Rietveld refinement shows that for the Fe-substituted compound, most of the Fe goes to the Mn site with a small amount at the Sn site, while in the Cr-substituted sample, all the Cr occupy the Mn site. However, the Sn site almost remains intact in the case of the Fe-substituted compound, while it is significantly disordered for the Cr-substituted sample as a fraction of Mn occupies the Sn site and an equivalent amount of Sn occupies the Mn site. XPS study shows that both Cr and Fe exist in the +3 oxidation state, while Mn exists in the +2 state and Sn exists in a mixture of +2 and +4 oxidation states. Magnetic property study of these substituted compounds shows different types of magnetism, which is attributed to the variation of d-electrons of the substituent atom. The chromium-doped compounds show ferrimagnetic character along with two transitions: one transition at ∼37 K and another at ∼152 K. However, in Fe-substituted Mn2SnS4 samples, the low-temperature transition disappears and an increase in the high-temperature antiferromagnetic ordering temperature i.e. from 152 K (Mn2SnS4) to 174 K (Mn1.82Fe0.18SnS4) is observed. The increase in the antiferromagnetic ordering temperature in Mn2-xFexSnS4 may be attributed to the increase in the covalence of Mn/Fe-S-Mn/Fe bonds (shorter) with iron substitution.

BiOCl Nanoplates Doped with Fe3+ Ions for the Visible-Light Degradation of Aqueous Pollutants

Two-dimensional (2D) layered ultrathin bismuth oxychloride nanoplate (BiOCl-UTN) photocatalysts are highly active only under ultraviolet light (energy band gap Eg: 3.0–3.1 eV). Herein, unlike using conventional closed-vessel high-temperature synthetic routes, we prepared unprecedented well-crystalline 2D Fe3+ ion-incorporated BiOCl-UTNs [Fe(III)-BiOCl-UTNs] having ultrathin thicknesses of about 4–5 nm and planar sizes of about 30–50 nm in an open vessel at room temperature and then used in photocatalysis under visible light. The present approach is poly(sodium 4-styrenesulfonate) (PSS)-aided, in which the formation of the distinct intermediate composite [PSS-Bi(OCH2CH2OH)-Fe3+] significantly inhibits the habitual spontaneous growth of BiOCl along the ⟨001⟩ plane and results in Fe(III)-BiOCl-UTNs. The synthesis shows robust reproducibility and allows large-scale production (5.2 g) with a well-controlled morphology, size, and thickness. Instead of using a tedious high-speed centrifugation process, the Fe(III)-BiOCl-UTN product is obtained via electrolyte sedimentation which is facile and cost-effective. The successful doping of Fe3+ ions into BiOCl-UTNs, the sustainable layered structure, and the stable lattice arrangement endow Fe(III)-BiOCl-UTNs with a narrower band gap (Eg: 2.55 eV). As-prepared Fe(III)-BiOCl-UTNs exhibit enhanced separation of photoexcited electrons–holes, rapid transfer of excited electrons to the surface, and significant potential to suppress electron–hole recombination. Consequently, under visible light, Fe(III)-BiOCl-UTNs achieved a substantially improved catalytic performance (>99%, five-cycle recyclability) to photoreduce Cr(VI) ions and photodegrade rhodamine B from aqueous solutions. The present performance surpasses pristine BiOCl-UTNs and state-of-the-art photocatalysts. Moreover, we disclosed the morphological optimization, predominant role of e– and •O2 radicals, and typical photocatalytic reaction mechanism. This work offers the first facile and cost-effective alternative to fabricate the iron-doped layered photocatalyst with superior catalytic activity, extendable for other functional materials and diverse practical applications.

A novel blue-emitting Sr2Gd8(SiO4)6O2:Bi3+ phosphor with oxyapatite structure

A series of Sr2Gd8(SiO4)6O2 (SGSO):xBi3+ (x = 0.005, 0.007, 0.010, 0.030 and 0.050) phosphors were successfully synthesized by a high-temperature solid-phase route. The X-ray powder diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared (FT-IR), ultraviolet–visible diffuse reflectance (UV–Vis DR), photoluminescence excitation (PLE) and emission (PL) spectra were utilized to evaluate the samples. The characterization results show that the PLE spectra monitored at 440 nm present a broad band with the maximum at 315 nm. Besides, the pure SGSO possesses the space group P63/m crystal structure, in which the low symmetry C3 or Cs sites favor the transition from 3P1 to 1S0 of Bi3+, thus produce strong blue emission. According to the calculation of concentration quenching, the critical distance of energy transfer (ET) between adjacent Bi3+ is 23.48 Å, and it is concluded that the quenching mechanism is attributed to d-d interaction. Eventually, the International Commission on Illumination (CIE) chromaticity coordinates of phosphors are located in blue region, which can be suitable for practical application in the field of the white light-emitting diode (WLED) and plasma display panels (PDPs).

A novel high color purity blue-emitting Tm3+-doped β-Ca3(PO4)2-type phosphor for WLED application

The series of Tm-doped phosphates Ca9-xZnxLa0.9(PO4)7:0.1Tm3+ for phosphor-convertible white LEDs (pc-WLED) with β-Ca3(PO4)2-type structure were synthesized using a standard high temperature route. Intense blue emission in the visible spectrum was observed due to 4f-4f transitions in the Tm3+ ion. The phosphates have been characterized by powder X-ray diffraction (PXRD), second harmonic generation (SHG), and luminescence spectroscopy. These phosphors show a satisfactory blue performance due to the 1D2 – 3F4 (≈ 450 nm) transition of Tm3+ excited by near-UV light (358 nm). The crystal structure transforms R3c → R3¯c upon Ca2+ → Zn2+ substitution, and it leads to growing of the integral intensity in 4 times compared with unsubstituted phosphate. Rising of color purity peaking at x = 1 was also observed. The obtained characteristics are superior to than that for the commercial blue phosphor BaMgAl10O17:Eu2+. Generally, Ca9-xZnxLa(PO4)7:Tm3+ phosphates are a new kind of potential blue emitting phosphors for white light-emitting diodes.

Bioprocessing of spent lithium ion batteries for critical metals recovery – A review

The increasing demand for metals and the concomitant depletion of the primary metallic resources is one of the most important environmental and societal challenges nowadays. Critical metals, rare earth elements, base and precious metals demand is growing day-by-day and driving many metals towards the edge of supply risk. On the other hand, the problems linked to waste generation (especially waste electrical and electronic equipment (WEEE)) are also increasing globally. These end-of-life electronic wastes contain significant concentration of critical raw materials accompanied by harmful substances. Spent Li ion batteries is a kind of WEEE stream, bearing considerable concentrations of valuable metals (like Co, Li, Mn and Ni). If the end-of-life Li ion batteries are not managed properly, there is a high risk that these valuable metals and toxic substances could end into the environment. In order to address the environmental complications, sustainable resource management and boost circular economy, it is important to properly manage and recycle these spent Li ionbatteries. Conventional methods based on high-temperature pyro-metallurgical routes together with hydro-metallurgical processing have been widely studied for the recovery of metals from spent LiBs. However, bio-metallurgical approaches have an edge over their counter parts because of their environmentally friendly nature. Microbe-metal interactions have received special attention both in terms of leaching metals from WEEE and also in recovering metal ions from aqueous streams. Microbial technologies are promising for removing metal ions because of less cost, technical feasibility for large scale applications and no need for addition of toxic chemicals thereby avoiding generation of toxic or hazardous byproducts. In this study, particular emphasis is placed on reviewing the progress made in biohydrometallurgy (i.e. bacterial and fungal leaching practices as one and two-step mode) for the leaching of critical metals from waste lithium ion batteries. Biotechnological methods (e.g. biosorption, bioprecipitation and bioelectrochemical treatment) for the recovery of critical metals from pregnant leachates and aqueous streams are also discussed.

Boosting the thermal stability and catalytic performance by confining Ag single atom sites over antimony-doped tin oxide via atom trapping

Catalysts based on single atoms of noble metals have attracted much research interest. However, single atoms are mobile and prone to sintering (forming large clusters) under reaction conditions, especially at elevated temperatures. Driven by the long-standing interest in the development of thermally stable catalysts, there is an urgent demand for synthesizing sintering-resistant single-atom catalysts. Here, we report a high-temperature self-assembly route to fabricate thermally stable silver (Ag) single-atom catalysts by confining Ag single atom sites over antimony-doped tin oxide (ATO) via atom trapping at 800 °C in air. Unique self-dispersion of Ag species takes place over the ATO support after high-temperature aging, contrary to a tendency of sintering or coalescence. Extended X-ray absorption fine structure (EXAFS) analysis confirms the presence of predominantly high dispersed isolated Ag species in Ag/ATO-800 °C aged sample. CO oxidation tests reveal that the stable single-atom Ag-on-ATO catalyst shows negligible decay and even a slight increase in experimentally observed activity after 800 °C aging. In contrast, the high temperature aging treatment causes serious catalyst deactivation, as expected for conventional Al2O3 supported noble metal catalyst. Our finding paves the way for using commercially available support to disperse and stabilize noble metal single atoms via atom trapping for the automotive CO oxidation reaction.

Studies of electrical, magnetic and leakage-current characteristics of double perovskite: Dy2CoMnO6

The structural, microstructural, dielectric, impedance, modulus, leakage–current and magnetic characteristics of a double perovskite compound Dy2CoMnO6 have been reported in this communication. We have synthesized the compound by a high-temperature mixed-oxide route. From the analysis of X-ray diffraction data, the structure of the material is found to be monoclinic with lattice parameters: a = 5.5070 Å, b = 5.5683 Å, and c = 7.7217 Å, β = 90.830. The morphological study suggests that the compound has an almost homogeneous scattering and distribution of grains over the surface with small voids. The frequency dependence of dielectric parameter has been discussed according to the Maxwell-Wagner model and different polarization mechanisms. In the study of temperature dependence of dielectric permittivity, we observe a dielectric anomaly that corresponds to the ferroelectric to paraelectric phase transition. In the impedance analysis, we also observe both positive and negative temperature coefficient of resistance (PTCR and NTCR) behavior of the material. The nature of frequency dependence of conductivity has been explained by the Jonscher power law, and thus the conduction process of the material belongs to the overlapping large polaron tunneling model. The activation energy obtained from the relaxation and conduction processes is found to support the process of electron hoping. An analysis of leakage current density characteristics shows that the conduction mechanism in the material follows the space charge limited conduction (SCLC) process. Study of the magnetic hysteresis loop of the material shows the anti-ferromagnetic type of behavior.

Electrical and magnetic properties of double perovskite: Y2CoMnO6

In this communication, the structural, micro-structural, dielectric, electrical, magnetic, and leakage-current characteristics of a double perovskite (Y2CoMnO6) ceramic material have been reported. The material was synthesized via a high-temperature mixed-oxide route. The compound crystallizes in a monoclinic structure which is confirmed from preliminary X-ray structural study. The morphological study by using scanning electron micrograph reveals the almost homogeneous distribution of grains throughout the surface of the sample. The nature of frequency-dependence of dielectric constant has been described by the Maxwell-Wagner model. The occurrence of a dielectric anomaly in the temperature dependence of dielectric permittivity study demonstrates the ferroelectric-paraelectric phase transition in the material. From the Nyquist plots, we found the existence of both grain and grain boundary effects. The frequency dependence of conductivity was studied by the Jonscher’s Power law, and the conduction phenomenon obeys the large overlapping polaron tunneling model. By using the Arrhenius equation, the activation energy has been calculated which is nearly equal to the energy required for the hoping of the electron. Both impedance and conductivity analysis demonstrate that the sample exhibits negative temperature coefficient of resistance (NTCR) properties indicating the semiconducting type of material at high temperatures. The anti-ferromagnetic character of the material is observed from the nature of magnetic hysteresis loop. The leakage current analysis suggests that the conduction process in the material follows the space charge limited conduction phenomenon. Such material will be helpful for modern electronic devices and spintronic applications.

Temperature stable (1-x)NaCa4V5O17-xBaV2O6 microwave dielectric ceramics for ULTCC applications

Novel temperature stable (1-x)NaCa4V5O17-xBaV2O6 (0.8≤x≤0.9, (1-x)NCV-xBV) ceramics were successfully synthesized through a high-temperature solid phase reaction route. XRD and SEM-EDS analysis demonstrated that only NaCa4V5O17 and BaV2O6 phases were formed without any extra phase. The introduction of BaV2O6 not only effectively improved the τf of NaCa4V5O17 matrix but also considerably lowered its sintering temperature to 550 °C. Typically, an approximate-zero τf value around −1.0 ppm/°C was achieved for 550 °C sintered 0.12NCV-0.88BV ceramics with low εr of 10.9 and Qxf of 15,500 GHz (at 10.3 GHz). Its good compatibility with Al electrode furthermore made 0.12NCV-0.88BV composites suitable for ULTCC applications.

Aqueous synthesis of PEGylated Ag2S quantum dots and their in vivo tumor targeting behavior

With significantly decreased light scattering and tissue autofluorescence, fluorescence imaging in the second near infrared (NIR-II, 1000-1700 nm) region has been heavily explored in biomedical field recently. Silver sulfide quantum dots (Ag2S QDs) with unique optical properties were one of the most classic NIR-II imaging probes. However, the Ag2S QDs for in vivo purpose were mainly obtain by oil phase-based high-temperature route at present. Here, we proposed a mild aqueous route to prepare NIR-II emissive Ag2S QDs for in vivo tumor imaging. Original Ag2S QDs was obtained by mixing sodium sulfide and silver nitrate in a thiol-terminated polyethylene glycol (mPEG-SH) solution. Treating the original Ag2S QDs with extra mPEG-SH ligands produced highly PEGyalted Ag2S QDs. These re-PEGylated Ag2S QDs exhibited much better blood circulation and tumor accumulation in vivo comparing with the original ones, which can serve as excellent tumor imaging probes. The whole-body blood vessel imaging of living mice was achieved with high resolution, the bio-distribution of these QDs were studied by NIR-II imaging as well. This work also highlighted the importance of ligand density for tumor targeting.

Structural Variations in Complex Sodium Thorium Arsenates

Three new sodium thorium arsenates, Na5Th4(AsO4)7 (1), Na5Th(AsO4)3 (2), and Na4Th(As2O7)2 (3) were synthesized via a high temperature route and their structures and optical properties were studied. Compound 1 adopts a three‐dimensional structure that consists of tetrameric fundamental building blocks (FBBs) [Th4(AsO4)7]5–, which are constructed by ThO8 and ThO9 polyhedra. The structures of 2 and 3 are based on open frameworks with channels running along the a or c axes, respectively, which are occupied by Na cations. Structural relations between the structures of 2 and 3 have been discussed regarding their composition. In contrast to the other two compounds, the arsenate anions in the structure of 2 play role of bridging ligands and do not connect more than two Th atoms. Owing to this, the underlying net of this compound contains only Th nodes has a lon topology. The Raman spectra of 1 and 2 contain similar peaks due to As–O vibrations of AsO4 groups, while the Raman spectrum of 3 differs significantly owing to the presence of As–O–As bridging group in As2O74– anions.

Investigation of Dielectric, Impedance and Conductivity Properties of 0.65Bi(Fe0.98Ga0.02)O3–0.35BaTiO3

The advancement in development of lead-free materials (ceramics, single crystal, thin film) acts as a forerunner to the stepwise progression in tailoring the performance of electronic devices. The perovskite-based lead-free ceramics are gaining lot of research interest due to their utilization in several electronic applications. The lead-free ceramics having chemical formula 0.65Bi(Fe0.98Ga0.02)O3–0.35BaTiO3 (further represented as BFG-BTO ahead) was synthesized employing the high-temperature mixed oxide route. The study aims toward the correlation of structural with electrical properties, exploring the relaxation and conduction mechanism persisting in the material. The single-phase formation in the prepared system is depicted through a powder X-ray diffraction technique suggesting a rhombohedral symmetry along with the cell parameters. The SEM presents surface morphology having high densification. The influence of gallium substitution modifies the electrical parameters of BaTiO3–BiFeO3 have been studied employing impedance meter in an extensive frequency (1 kHz–1 MHz) and temperature (25–450 °C). The grains, grain boundaries, electrode effect are revealed by impedance spectroscopy at different temperatures and frequencies. The ferroelectric nature of the sample is ascribed by the P–E loop of the material.

Study on effect of TiB2 reinforcement on the microstructural and mechanical properties of magnesium RZ5 alloy based metal matrix composites

Abstract A self-propagating high-temperature synthesis route is adopted for the fabrication of TiB2-reinforced magnesium RZ5 alloy-based in-situ metal matrix composites. Ti-B is used according to the appropriate stoichiometry to obtain 4, 6 and 8 wt.% TiB2 reinforcements. The base alloy and cast composites are solutionised to enhance the mechanical properties of the materials. A microstructural study of the composites is carried out using optical microscopy and field emission scanning electron microscopy (FESEM) and revealed near-uniform distribution of TiB2 particles in the magnesium RZ5 alloy matrix. X-ray diffraction revealed the formation of the TiB2 reinforcement along with the transient phase TiB and MgB7. The hardness of the RZ5 alloy-based composites increases by 7.12%, 17.06% and 32.07% with the addition of 4, 6 and 8 wt.% TiB2 reinforcements, respectively. The ultimate tensile strength of the as-cast composite increases by 30.47% with the addition of 8 wt.% TiB2. The tensile strength and ductility of the materials is improved by using the solutionising heat treatment. The heat-treated composite containing 8 wt.% TiB2 results in an ultimate tensile strength of 178.7 MPa. The tensile fracture surfaces are analysed using FESEM. The wear loss of the materials decreased from 25.826 mm3 to 22.949 mm3 by the adding 8 wt.% TiB2 for the sliding distance of 2000 m. Micrographs of the worn surfaces obtained from FESEM of both the base alloy and composites are also studied which indicate delamination, wear groove and oxide formation.

Abrasive Wear Behaviour of TiB2 Reinforced In-Situ Synthesized Magnesium RZ5 Alloy based Metal Matrix Composites

Abrasive wear behaviour of TiB2 reinforced in-situ magnesium RZ5 alloy-based metal matrix composites was investigated using a pin-on-disc wear testing apparatus. The in-situ RZ5/TiB2 composite was synthesized through the self-propagating high-temperature synthesis route. The microstructure of the composite revealed a near-uniform distribution of TiB2 in magnesium matrix. The abrasive wear behaviour on the base RZ5 alloy and TiB2 reinforced composites were investigated in terms of weight loss and co-efficient of friction. The effect of varying applied load (10–30 N), sliding distance (1000–3000 m), and wt% of TiB2 content on abrasive wear properties were analysed. The results indicated a higher wear loss of the materials with increase in the applied load and sliding distance. Co-efficient of friction decreased with increase in the applied load but increased with increase in sliding distance. The morphology of the worn surface under different test conditions was analysed in terms of delamination, wear groove, oxide, and wear debris formation using field emission scanning electron microscope. Large flaky shape wear debris was noticed when the load applied is 30 N whereas equiaxed wear debris was noticed when the applied load is 10 N. Increase in sliding distance increased the contact temperature led to the formation of the oxide layer on the contact surface.

Photoinduced charge transfer studies of type-II core-shell ZnTe-ZnSe quantum dots

In this communication, we discuss the photoinduced charge transfer between type-II ZnTe-ZnSe core-shell quantum dots and a molecular adsorbate methyl viologen. The oleic acid-capped core-shell nanostructures were synthesized using organometallic high-temperature route and were characterized using UV-visible absorption spectroscopy, photoluminescence spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy, selected area electron diffraction, inductive coupled plasma optical emission spectroscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The charge transfer behaviour of the core-shell quantum dots in the presence of methyl viologen was investigated by monitoring variations in photoluminescence and life time using steady-state and time-resolved techniques, and the results indicated static processes in the charge transfer interactions. The charge transfer capability of a core-shell system is extremely important while considering it in photovoltaic applications.

Synthesis and characterization of single phase ZnO nanostructures via solvothermal method: influence of alkaline source

Single phase ZnO nanostructures were synthesized by simple and low temperature solvothermal process from two different alkaline sources; Potassium hydroxide (KOH) and Sodium hydroxide (NaOH) with zinc acetate dihydrate (Zn(CH3COO)2∙2H2O) as precursor. This facile and rapid synthesis technique achieve high purity of Zinc oxide (ZnO) nanostructures on large scale negating the use of complex and high temperature routes. The synthesized particles were characterized by X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDX), Fourier Transform Infrared (FT-IR) Spectroscopy, Ultraviolet Visible (UV-Vis) spectroscopy and Brunauer-Emmett-Teller (BET) analysis. ZnO synthesized using KOH and NaOH exhibit wurtzite hexagonal and flake-like nanostructures with average crystallite size of 11.0 nm and 14.9 nm respectively. Surface area of 59.50 m2/g and 31.43 m2/g were determined for KOH and NaOH sources respectively. The optical absorption spectra of the two samples showed absorption bands of 367.70 and 365.30 nm. The results showed the effect of alkaline sources on the surface morphology, structural and optical properties of ZnO.

Ferrimagnetic semiconductor with a direct bandgap

The direct bandgap nature of semiconductors is crucial for a wide range of optoelectronic devices and energy applications. These materials are mainly concentrated in hybrid organic–inorganic halide perovskites, III–V semiconductors, and monolayer transition metal dichalcogenides. Here, we report an AA′3B2B′2O12-type direct bandgap semiconductor CaCu3Fe2Ta2O12 using spin-polarized density functional theory calculations. The formation energy indicates that this material is thermodynamically preferred under a high-temperature and high-pressure synthetic route, similar to the analog CaCu3Fe2Nb2O12. Effective ferrimagnetic interaction occurs through the antiferromagnetic coupling between the A-site Cu and B-site Fe. More importantly, CaCu3Fe2Ta2O12 exhibits semiconducting behavior with a direct bandgap in the visible range, suggesting that AA′3B2B′2O12-type quadruple perovskites are potential candidate materials in photovoltaics as well as in optoelectronic devices.

Effects of mixing processes on the property of the LiFePO4/C cathode material via high-temperature ball milling route

[Formula: see text] samples were obtained via high-temperature ball milling route with different mixing processes. Ultrasonic radiation and wet mechanical agitation were used as mixing processes, respectively. The effects of different mixing processes on the structure and electrochemical performance of [Formula: see text] were investigated. The results exhibited that [Formula: see text] prepared by high-temperature ball milling with ultrasonic irradiation as mixing processes displayed the best rate capability and cycle stability among all the samples: it delivered discharge capacities of [Formula: see text] (0.1 C), [Formula: see text] (5.0 C) and [Formula: see text] (10 C) [Formula: see text], respectively. The discharge capacity was [Formula: see text] [Formula: see text] at 0.5 C-rate over 100 cycles with capacity retention of 95.0%. It is concluded that ultrasonic irradiation is an effective mixing process for the preparation of [Formula: see text] cathode material via high-temperature ball milling route.

The crystal site engineering and turning of cross-relaxation in green-emitting β-Ca3(PO4)2-related phosphors

Series of Tb3+-doped phosphates Ca9–xZnxTb(PO4)7 and Ca9–xZnxLa0.99(PO4)7:0.01 Tb3+ with β-Ca3(PO4)2-type structure were synthesized using a standard high temperature route. The luminescence properties of these compounds were determined by the photoluminescence emission (PL), the excitation (PLE) spectra and lifetime measurements. A green-emitting LED device was fabricated using the most effective one. No concentration quenching was detected in the whole region of solid solutions. Upon Ca2+ → Zn2+ substitution the crystal structure transformation from the polar to centrosymmetric. The ways of control the PL spectra and cross-relaxation process were determined. In both solid solutions a “green” magneto-dipole 5D4 → 7F5 transition is predominant. The integral intensity increases in 3 times in the most effective Ca8ZnTb(PO4)7 phosphor. The measured quantum yields (QY) reached 31%. Thus, a target substitution of Ca2+ by Zn2+ is a new path for crystal site engineering and allows to obtain an efficient green luminescence of Tb3+ ions in the β-Ca3(PO4)2-type hosts.