Fuyang Liu

Hydrothermal approach and luminescent properties for the synthesis of orthoniobates GdNbO4:Ln3+ (Ln = Dy, Eu) single crystals under high-temperature high-pressure conditions

Single crystal GdNbO4:Ln3+ (Ln = Dy, Eu) phosphors were prepared via a high-temperature high-pressure hydrothermal procedure at 650 °C under autogenous pressure. X-ray diffraction, field emission scanning electron microscopy, photoluminescence, Raman and XPS were utilized to characterize the as-synthesized phosphors. XRD reveals that the samples begin to crystallize at 550 °C and a pure GdNbO4 phase can be obtained at 650 °C. FE-SEM images indicate that GdNbO4:Ln3+ (Ln = Dy, Eu) samples consist of fine sheets with a size of 50–100 μm. Under UV excitation, the GdNbO4:Eu3+ and GdNbO4:Dy3+ phosphors showed the characteristic emissions of Eu3+ are 5D0 → 7FJ (J = 0, 1, 2, 3, 4), and Dy3+ (4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions), respectively. The preparation method presented here dramatically lowered the traditional temperature of 2300 °C or above in the Czochralski method. The GdNbO4:Dy3+ single crystals showed a bright white emission under different excitation wavelengths with a relatively high quantum yield of 21.7%. The GdNbO4:0.05Eu3+ exhibited excellent bright red luminescence at 612 nm under near-UV excitation, narrowed emission spectra, room temperature luminescence lifetimes of milliseconds and maximum quantum efficiencies of 43.2%.

High-temperature, high-pressure hydrothermal synthesis, crystal structure and photoluminescent properties, of K3[Gd1−xTbxGe3O8(OH)2] (x = 0, 0.3, 0.1, 1)

A family of 2D-layered lanthanide germanates K3[Gd1−xTbxGe3O8(OH)2] (x = 0, 0.3, 0.1, and 1), have been synthesized by a high-temperature, high-pressure hydrothermal method and characterized by single-crystal X-ray diffraction, photoluminescence, IR spectra, and Energy-Dispersive Spectroscopy (EDS). The X-ray powder diffraction patterns of these compounds reveal that they are isostructural. The single-crystal X-ray diffraction analysis of K3[GdGe3O8(OH)2] reveals that it is a 2D-layered [LnGe3O8(OH)2]n3n− anionic framework which is built up from GeO4H/GeO4 tetrahedra and GdO6 octahedra by sharing vertex O atoms. K+ ions locate in the free void space to achieve the charge balance of the framework. A sample containing only Tb3+ emits mainly from one transition, 5D4 → 7F5 (552 nm). Mixed lanthanide samples, K3[Gd1−xTbxGe3O8(OH)2] (x = 0.3, and 0.1), have also been prepared and efficient Gd → Tb energy transfer has been observed.

Microwave-assisted synthesis of Cu2O microcrystals with systematic shape evolution from octahedral to cubic and their comparative photocatalytic activities

Cuprous oxide (Cu2O) microcrystals with systematic shape evolution were successfully synthesized via a facile microwave-assisted heating technique. The monodispersed Cu2O was synthesized using copper acetate as a starting material, ethylene diamine tetraacetic acid (EDTA) as a reducing agent and surface-regulating agent and a mixture of water and n-butyl alcohol as reaction solvent. Various morphologies of Cu2O microcrystals, including octahedral, truncated octahedral, cuboctahedral, truncated cubic and cubic microcrystals, were obtained by altering the volume ratio of n-butyl alcohol to water. The morphologies and optical properties of the synthesized Cu2O microcrystals were characterized by XRD, SEM, TEM, HRTEM, SADE and UV-Vis/DRS. The growth mechanism of these crystals was thereby proposed. The volume ratio of n-butyl alcohol to water in the reaction medium was a critical factor in precisely controlling the morphologies of the microcrystals. Furthermore, their comparative photocatalytic activities for the degradation of methyl orange were tested.

Selective synthesis of cubic and hexagonal phase of CuInS2 nanocrystals by microwave irradiation

Metastable cubic zincblende and hexagonal wurtzite CuInS2 nanocrystals were successfully synthesized by a facile microwave radiation method. The morphology, structure and phase composition of the as-prepared products were examined, and the results demonstrated that high-purity and uniform CuInS2 nanocrystals were obtained. Further investigation revealed a structural evolution process from cubic zincblende to hexagonal wurtzite with increasing volume ratio of ethylenediamine and ethanol from 1:30 to 1:1 at 160 °C. In addition, the optical absorption properties of samples were also studied. It was found that the as-synthesized cubic and hexagonal CuInS2 nanocrystals had band gaps of 1.503 and 1.470 eV, respectively. Thanks to the superior optical absorption properties for visible light, CuInS2 nanocrystals may have potential applications in various nanostructured optoelectronic devices. The possible formation mechanism of the product, namely “phase transformation”, was systematically studied.

Microwave synthesis and photocatalytic activity of Tb3+ doped BiVO4 microcrystals

Tb(3+) doped BiVO4 has been successfully synthesized by a simple microwave-assisted hydrothermal method at 140°C for 30min. The structure, morphology and optical property of the Tb(3+) doped BiVO4 products have been systematically investigated. This study indicates that the incorporation of Tb(3+) could induce the conversion of structure from monoclinic to tetragonal for BiVO4. Furthermore, the as-obtained Tb(3+) doped BiVO4 samples showed an obvious morphological change: the hollow square rod-like BiVO4 crystal gradually changed to spindle-like crystal. The Tb(3+) doped BiVO4 products exhibited extraordinary photocatalytic activity for Methylene Blue (MB) degradation under visible light irradiation. The doped BiVO4 at a molar ratio of 2at% (Tb and Bi) with a mixture of monoclinic and tetragonal phases showed and prominent photocatalytic degradation rate, which reached 99.9% in 120min. The results suggest that the differences in the photocatalytic activity of these BiVO4 crystals with different Tb(3+) doping concentrations can be attributed to the change of crystalline phases, and the coexistence of the monoclinic/tetragonal phases in BiVO4 products, which improve the efficient charge separation and transportation.

Synthesis, crystal structure, and luminescence properties of a new microporous europium silicate: Na3EuSi6O15·1.47H2O

A new microporous europium silicate, Na3EuSi6O15·1.47H2O (denoted as 1), was synthesized under high-temperature and high-pressure conditions, and structurally characterized by single-crystal and powder X-ray diffraction (XRD) analysis. The single-crystal XRD analysis of 1 revealed that its structure is based on corrugated silicate single layers with the composition [Si2O5] in the ab plane containing 4-, 5-, 6-, and 8-rings, which are connected together by EuO7 polyhedra via vertex oxygen atoms forming a three-dimensional framework of 1. Compound 1 contains 4, 8-ring channels along the [100] direction and 5-, 6-ring channels along the [001] direction delimited by SiO4 tetrahedra and EuO7 polyhedra. The Na+ ions are located in the free void space to balance the charge. The photoluminescence properties of 1 were also investigated.

Synthesis of perovskite-type manganites Yb1−xDyxMnO3 (0.1 ≤ x ≤ 0.5) via solid-state reaction and high-pressure flux methods followed by structural characterization and magnetic property studies

A series of hexagonal perovskite-type compounds Yb1−xDyxMnO3 (0.1 ≤ x ≤ 0.5) have been prepared by the traditional solid-state reaction method at 1573 K, and a single crystal orthorhombic perovskite-type compound Yb0.5Dy0.5MnO3 has also been obtained by a high-pressure flux method at 1273 K under 5 GPa high pressure. Final products are fully characterized by XRD and XPS analyses, and then subject to magnetic measurements. It appears that the hexagonal Yb1−xDyxMnO3 (0.1 ≤ x ≤ 0.5) compounds have shown antiferromagnetic properties with a Neel temperature of 10 K, and canted antiferromagnetic behaviour is clearly evident at a lower temperature. Also, it is found that the magnetization of Yb1−xDyxMnO3 increases with the increase of Dy content. The orthorhombic Yb0.5Dy0.5MnO3 single crystal has been found to be paramagnetic, differing from RMnO3 reported in the literature, which is antiferromagnetic due to subtle structural difference.