摘要 :
The spectroscopic properties of Eu3+-doped Bi12SiO20 (BSO) were investigated and compared with that of Eu3+-doped Bi12GeO20 (BGO). The emission properties and the absorption spectra have been measured at 10 K as well as at 300 K (...
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The spectroscopic properties of Eu3+-doped Bi12SiO20 (BSO) were investigated and compared with that of Eu3+-doped Bi12GeO20 (BGO). The emission properties and the absorption spectra have been measured at 10 K as well as at 300 K (room temperature). Luminescence was detected due to the direct excitation of the 5D0 level of Eu3+, as well as through the excitation of the 5D1 level. The Judd-Ofelt theoretical framework was used to compute the radiative lifetimes (τ) and the omega parameters (Ωλ). The electric dipole transition probabilities, asymmetry ratios (R), along with the branching ratios (β) were also determined based on the obtained experimental data. The strongest detected luminescence belongs to the 5D0 → 7F0 transition observed at 578 nm, similar to the BGO sillenite. Reasons for the major presence of the 5D0 → 7F0 emission, theoretically forbidden by the Judd-Ofelt Theory, were investigated and compared with that of the BGO sillenite. Obtained results showed that the strong 5D0 → 7F0 line is also present in Eu:BSO, indicating that this is a feature of the entire sillenite family and not just Eu:BGO.
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The sites of incorporation of Cu2+ impurity ions in Bi12GeO20 single crystals co-doped with copper and vanadium have been investigated by electron paramagnetic resonance (EPR). While the X-band EPR spectra consist of a simple broa...
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The sites of incorporation of Cu2+ impurity ions in Bi12GeO20 single crystals co-doped with copper and vanadium have been investigated by electron paramagnetic resonance (EPR). While the X-band EPR spectra consist of a simple broad (Delta B similar to 50 mT) line with anisotropic lineshape, the W-band EPR spectra exhibit well resolved, strongly anisotropic lines, due to transitions within the 3d(9)-D-2 ground manifold of the Cu2+ ions. The most intense group of lines, attributed to the dominant Cu2+(I) center, displays a characteristic four components hyperfine structure for magnetic field orientations close to a < 110 > direction. The g and A tensor main axes are very close to one of the 12 possible sets of orthogonal < 1-10 >, < 00-1 > and < 110 > crystal directions. Several less intense lines, with unresolved hyperfine structure and similar symmetry properties, mostly overlapped by the Cu2+(I) spectrum, were attributed to Cu-2 (+)(II) centers. The two paramagnetic centers are identified as substitutional Cu2+ ions at Bi3+ sites with low C-1 symmetry, very likely resulting from different configurations of neighboring charge compensating defects. (C) 2015 Elsevier Inc. All rights reserved.
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We report on the fabrication and characterization of Nd-doped Bi2O3-GeO2/SiO2 glass. The glass samples were synthesized by melt quenching procedure and characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectrosc...
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We report on the fabrication and characterization of Nd-doped Bi2O3-GeO2/SiO2 glass. The glass samples were synthesized by melt quenching procedure and characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Near-infrared (NIR) emission was found at about 1065 nm under 590 nm and 808 nm laser diodes (LDs) excitation. The highest stimulated emission cross-section (ECS, sigma(em)) for the luminescence of 1065 nm can reach up to 3.89 x 10(-20) cm(2). The markedly increased absorption at 808 nm contributes to the strong emission at 1065 nm (808 nm pump) in Nd-doped Bi2O3-GeO2/SiO2 glasses. The Nd-doped Bi2O3-GeO2/SiO2 glass can be exploited as a good optical laser material. (C) 2018 Elsevier GmbH. All rights reserved.
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The possibility of partial substitution of Si for Ge in the structure of Bi2GeO5 during synthesis from the melt and the effect of the substitution on the structure of the synthesized material have been studied. The microstructure ...
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The possibility of partial substitution of Si for Ge in the structure of Bi2GeO5 during synthesis from the melt and the effect of the substitution on the structure of the synthesized material have been studied. The microstructure of the synthesized compounds after their complete decomposition has been investigated. Using the phase powder X-ray diffraction- and optical microscopy methods, it has been found that metastable phases of bismuth silicate and germanate with structures of the Aurivillius type form a continuous series of solid solutions. It is shown that a mixed structure composed of large Bi4Si(Ge)(3)O-12 crystals and the Bi12Si(Ge)O-20 + Bi4Si(Ge)(3)O-12 point eutectic is obtained after the decomposition of compounds of the Bi2SiO5-Bi2GeO5 quasi-binary system, regardless of the percentage of substitution of Si for Ge. Upon slow heating up to annealing temperatures (at a rate of 13.5 degrees C/min), a structure of decomposition that is more finely dispersed and uniform than the structure obtained upon rapid heating (when charg the material into an already preheated furnace), which is more coarsely grained and inhomogeneous. Moreover, regions with a large structure similar to a dendritic one can appear in the material when the contents of silicon and germanium oxides in the alloy are close to each other (20/30-30/20 mol %). Such regions differ slightly in chemical composition from the surrounding material and appear during both slow and rapid heating of the material to annealing temperatures.
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The properties of a tetrahedron containing Bi(2)AO(5) (A=Si, Ge) are examined using Ab initio calculations and symmetry mode analysis. Stabilization of the polar phase is observed in both compounds with a monoclinic Cc phase. In t...
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The properties of a tetrahedron containing Bi(2)AO(5) (A=Si, Ge) are examined using Ab initio calculations and symmetry mode analysis. Stabilization of the polar phase is observed in both compounds with a monoclinic Cc phase. In the monoclinic ground state, the tilting angle (phi(1)) of tetrahedron is 7.21 degrees and 21.94 degrees for the Si and Ge compound, respectively. The relationship between a primary order parameter and the tetrahedral tilting is identified and an analytical formula between them is proposed by analyzing the structure. The detailed layer-by-layer polarization calculations shows that the main polarization component originates from the tetrahedron tilting of the AO(4) unit, and the analytical relationship between the primary order parameter and spontaneous polarization is also calculated. This B3LYP hybrid functional calculation provides a band gap of 4.44 eV and 4.18 eV for Bi2SiO5 and Bi2GeO5, respectively. The main difference between the two compounds is also analyzed based on the electronic structure and electron localization function analysis. (C) 2015 Elsevier Inc. All rights reserved.
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Glasses based on the system of Sm2O3-Bi2O3-GeO2 were prepared, and their electronic polarizabilities and formation behavior of Bi2GeO5 (monoclinic) and Bi4Ge3O12 (cubic) crystals were clarified. The glasses showed large electronic...
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Glasses based on the system of Sm2O3-Bi2O3-GeO2 were prepared, and their electronic polarizabilities and formation behavior of Bi2GeO5 (monoclinic) and Bi4Ge3O12 (cubic) crystals were clarified. The glasses showed large electronic polarizabilities (alpha(o2-)(n)) and optical basicities (Lambda(n)), e.g., alpha(o2-)(n) = 2.783 angstrom(3) and Lambda(n) = 1.070 for 50Bi(2)O(3)-50GeO(2) glass, indicating a basic nature in the glasses. The small addition of Sm203 was found to be effective for the control of the crystallization of Bi2O3-GeO2 glasses. Sm3+-doped Bi2GeO5 nanocrystals with an ellipsoidal shape (a(long)- 32 nm b(short)-20 nm) and Sm3+-doped Bi4Ge3O12 nanocrystals with a spherical shape (-7 nm) were formed in the glass-ceramics of 5Sm(2)O(3)-45Bi(2)O(3)-50GeO(2) and 5Sm(2)O(3)-31Bi(2)O(3)-54GeO(2)-10B(2)O(3), respectively. Highly oriented crystal lines consisting of Bi2Ge05 or Bi4Ge3O12 were patterned at the glass surface by continuous wave Yb:YV04 fiber laser (wavelength: 1080 nm) irradiations, suggesting the possibility of the design and control of spatially selected crystallization in Bi2O3-GeO2 based glasses. (C) 2017 Elsevier B.V. All rights reserved.
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Bi12GeO20-based composites Bi12GeO20-Bi2S3 (BGS) were successfully constructed through a facile ball-milling method using sulfur powder for the first time. Systematical analyses verified the in-situ generation of n-p heterojunctio...
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Bi12GeO20-based composites Bi12GeO20-Bi2S3 (BGS) were successfully constructed through a facile ball-milling method using sulfur powder for the first time. Systematical analyses verified the in-situ generation of n-p heterojunctions with surface oxygen vacancies (OVs). These composites showed reinforced photocatalytic removal of NO at ppb level under visible light with high selectivity for NO2- /NO3- species, avoiding the generation of toxic NO2 as far as possible. Especially, the best candidate BGS0.1 possessed 46% NO removal with 96% selectivity for NO2-/NO3- species that were much higher than those by Bi12GeO20, mainly relevant to the enhanced visible-light absorption, synergistic effect of heterojunctions containing surface OVs to promote charge carriers segregation and reactive radicals formation, and suitable phase composition with proper band structures. The effect of heterojunctions with surface OVs over band structures and reaction paths was demonstrated by density functional theory (DFT) calculation. DRIFTS and FT-IR spectra were recorded to deduce NO conversion routes. Eventually, a preliminary photocatalysis mechanism of these robust composites was conjectured in a Zscheme manner basing experimental and analytical results. This study might pave roads for in-situ construction of sillenite-based composites with surface OVs by a mechanochemical approach with satisfactory photocatalytic NO treatment under visible light.
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In the present work, the photoluminescence (PL) spectra of bismuth germanate (BGO) doped with trivalent rare earth element (REE) ions with different doping concentrations (0.03 wt% Eu, 0.4 wt% Tm, and 1.1 wt% Nd) are reported in t...
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In the present work, the photoluminescence (PL) spectra of bismuth germanate (BGO) doped with trivalent rare earth element (REE) ions with different doping concentrations (0.03 wt% Eu, 0.4 wt% Tm, and 1.1 wt% Nd) are reported in the temperature range from 10 to 300 K using different detectors, namely, photomultiplier tube (PMT), InGaAs (IGA), and Si. The luminescence in the NIR region was also measured at room temperature. Two broad emission bands attributed to undoped BGO were found at circa 1350 and 1800 nm, respectively. The broad-band emissions are replaced by narrow-band line emissions defined by the trivalent rare earth dopants. The emission spectra from rare earth ion-doped BGO extend from 500 to 2000 nm. Rare earth ions act as the dominant recombination centers and define the emission spectra. This is interpreted as resulting from direct charge transfer from intrinsic defect traps to rare earth recombination centers. The temperature-dependent luminescence of BGO doped with 0.4 wt% Tm is also presented.
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The Yb-doped Bi2O3-GeO2 glasses were prepared by the conventional melt quenching technique. Near infrared (NIR) broadband emission was found at about 1024 nm, and 1330 nm (under 785 nm excitation), and the measured fluorescent lif...
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The Yb-doped Bi2O3-GeO2 glasses were prepared by the conventional melt quenching technique. Near infrared (NIR) broadband emission was found at about 1024 nm, and 1330 nm (under 785 nm excitation), and the measured fluorescent lifetime was about several hundred microseconds. The emission intensity of Yb-doped Bi2O3-GeO2 glasses increased with increasing of Yb dopant in our experiments. The NIR emission should be related to Yb3+ and lower valence Bi ions. (C) 2015 Elsevier B.V. All rights reserved.
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In this study, various plasmonic binary composites Ag-Bi12GeO20 were fabricated through a facile in-situ photoreduction route and subsequently analyzed by multitudinous techniques. The presence of both desirable ingredients in het...
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In this study, various plasmonic binary composites Ag-Bi12GeO20 were fabricated through a facile in-situ photoreduction route and subsequently analyzed by multitudinous techniques. The presence of both desirable ingredients in heterojunction structures were confirmed by XPS, SEM, TEM, and EDS elemental mapping and band structures were analyzed by UV-Vis DRS spectra. Moreover, steady-state and transient PL and electrochemical spectra were recorded to reveal effective spatial separation of charge carriers. The effective separation of charge carriers, reinforced visible-light absorption by local surface plasmon resonance effect of Ag nanoparticles, appropriate phase composition, and enlarged specific surface areas contributed to enhanced catalytic degradation of organic dye RhB and antibiotic TC and reduction of Cr (VI) under visible light. Specifically, the best candidate 1AB exhibited apparent reaction rate constants over degradation of RhB and TC and reduction of Cr (VI) about 5.0, 1.72, and 5.77 times those of bare Bi12GeO20 under the identical condition. In addition, basing on experimental and electrochemical analyses a possible photocatalysis mechanism was speculated for these robust and recyclable plasmonic binary composites. Such investigation would provide a novel alternative plasmonic system for environmental protection and mediation by means of photocatalytic technology.
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