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1.
《Materials Research Bulletin》2013,48(11):4947-4952
60ZnCl2–20KCl–20BaCl2xTbCl3 glasses (x = 0.10, 0.25, 0.50, 0.75, 1.00, and 1.25) were prepared by melt-quenching method, and Tb3+ fluorescence properties were investigated under 355 nm excitation. Regardless of x values, the electrons that were relaxed from the 5D3 to 5D4 level of Tb3+ ions by the multiphonon relaxation, were repressed to 28% of all the excited electrons because the ZnCl2-based glass had much lower phonon energy than oxide glasses. For 0 < x  0.34, the cross relaxation, (5D3  5D4)  (7F0  7F6), was repressed, and consequently 72% and 28% of all the excited electrons were radiatively relaxed by the 5D3  7FJ (J = 6, 5, 4, 3, and 2) and 5D4  7FJ (J = 6, 5, 4, and 3) transitions, respectively. The lifetimes of the 5D3 and 5D4 initial levels were obtained to be 1.1 and 2.1 ms, respectively.  相似文献   

2.
《Materials Research Bulletin》2013,48(11):4687-4692
Epitaxial films of Ce-doped Gd3(AlxGa1−x)5O12 with x = 0.00, 0.22, 0.31, 0.38 formula units were grown using liquid-phase epitaxy method, and their optical properties were studied. The emission of Ce3+ ions can be observed only when Al3+ ions are incorporated into the garnet structure, resulting in a shift of the 5d Ce3+ states from the conduction band to the bandgap. It is shown that the shift is caused by the cumulative effect of gradual low-energy shift of the lowest 5d level of Ce3+ and the raise of the garnet bandgap energy with increasing Al3+ concentration.  相似文献   

3.
Synthesising and characterizing of the FePS3 layered compound and its intercalation with pyridinium ion (pyH+) were studied. Well-crystallized material of FePS3 was formed. Full insertion of pyH+ was assured by X-ray diffraction (XRD) measurements. Two phases were produced due to intercalation, phase A (d = 12.1 Å) and phase B (d = 9.7 Å). There is a phase transformation of phase A to phase B. As a result of intercalation, there was a change in symmetry of the host lattice from C2/m to R-3m. The intercalated compounds, phase A and phase B, could be described by a trigonal unit cell and the lattice parameters a = b = 3.5026 Å, and different values of the cell parameter c, which is lengthened due to increasing of the d-spacing (the interlayer space increases by 5.7 and 3.3 Å of phase A and phase B, respectively), and γ = 120°. Infrared spectra (IR) showed the presence of the strong peak of FePS3 at 570 cm−1, which was splitted due to complete intercalation to two or three peaks. As a result of elemental analysis, there is a loss of Fe2+ cations due to the intercalation process, and so the intercalated guest species must be mainly present as pyH+ to balance electrical charge (i.e. the intercalation of FePS3 with pyH+ is a non-redox intercalation).  相似文献   

4.
《Materials Research Bulletin》2013,48(11):4896-4900
The europium(III)-doped yttrium oxysulfate (Y2O2SO4:Eu3+) nanopieces have been prepared via electrospinning followed by calcination at 1000 °C in mixed gas of sulfur dioxide and air. Based on the experimental results, a possible formation mechanism for the nanopieces is that the nanopieces are determined by the directing template of electrospun nanoribbons and the multilayer crystal structure of Y2O2SO4. Besides, the nanopieces show excellent luminescent properties with emissions at 581, 589, 597, 653, 619, and 697 nm resulting from the 5D0  7FJ (J = 0, 1, 2, 3, 4) transition of Eu3+. The peaks of charge transfer and 5D0  7F2 transition of Eu3+ obviously have red shifts comparing to those of both Y2O3:Eu3+ nanoribbons and commercial Y2O3:Eu3+. Moreover, the nanopieces exhibit stronger intensities than the Y2O3:Eu3+ in excitation and emission spectra. Concentration quenching in the nanopieces occurs when Eu3+ concentration is 11 mol%, indicating that the nanopieces have an optimum luminescent intensity under this doping concentration.  相似文献   

5.
This paper presents the method for measurement of the adhesion force and fracture strength of the interface between ceramic particles and metal matrix in ceramic reinforced-metal matrix composites. Three samples with the following Cu to Al2O3 ratio (in vol.%) were prepared: 98.0Cu/2.0Al2O3, 95.0Cu/5.0Al2O3 and 90Cu/10Al2O3. Furthermore, microwires which contain a few ceramic particles were produced by means of electro etching. The microwires with clearly exposed interface were tested with use of the microtensile tester. The microwires usually break exactly at the interface between the metal matrix and ceramic particle. The force and the interface area were carefully measured and then the fracture strength of the interface was determined. The strength of the interface between ceramic particle and metal matrix was equal to 59 ± 8 MPa and 59 ± 11 MPa in the case of 2% and 5% Al2O3 to Cu ratio, respectively. On the other hand, it was significantly lower (38 ± 5 MPa) for the wires made of composite with 10% Al2O3.  相似文献   

6.
《Materials Research Bulletin》2013,48(11):4733-4737
This study investigates the emission properties of the Er3+/Nd3+ ions codoped 70GeS2–10In2S3–20CsBr chalcohalide glasses. The vacuumed melt-quenching technique is employed to synthesize the glasses. The absorption spectra, upconversion and near-IR emission spectra as well as fluorescence decay curves are collected. With the increasing concentration of Er3+ ions, the lifetimes at 1073 nm for Nd3+ ions decrease from 538 to 420 μs under 808 nm excitation. Meanwhile, the lifetimes at 1540 nm for Er3+ ions decrease from 245 to 214 μs with the increasing concentration of Nd3+ ions. The emission spectra and lifetimes show that energy transfer exists between the Nd3+ and Er3+ ions. The luminescence and detailed energy transfer mechanisms are schematically proposed.  相似文献   

7.
This paper is aiming to analyze the effects of electron beam irradiation on the mechanical properties and structural–morphology of nano-sized montmorillonite (MMT) added polyvinyl alcohol (PVOH) composite. MMT particles were added to the PVOH matrix at various loading level that ranges from 0.5 to 4.5 phr MMT and electron beam irradiated with dosages ranging from 6 to 36 kGy. The results showed that tensile strength of MMT added PVOH composites at 1.5 and 2.5 phr MMT were observed marginally higher compare to neat PVOH when irradiation dosages increased to 26 kGy. However, when the concentration of MMT exceeded 2.5 phr, the application of irradiation seems to cause adverse effect to the PVOH–MMT composite. Besides, according to the X-ray diffraction analysis, the application of low irradiation dosage (⩽16 kGy) has significantly enhanced the intercalation effect of MMT particles at high loading (4.5 phr) in PVOH matrix. This also found to be consistent with the scanning electron microscopy observation where the dispersion of MMT particles in PVOH matrix was noted to be more homogeneous than non-irradiated samples. Further increment in irradiation dosage up to 36 kGy has significantly reduced the crystallinity which indicates the higher radiation energy could rupture the crystallite structures in PVOH matrix.  相似文献   

8.
The extraordinary mechanical properties of single-wall carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs) have generated interest in incorporating them as toughening agents in ceramics. This work describes the fracture behaviour of an alumina (Al2O3) ceramic reinforced with a mixture of 0.05 wt% MWCNTs + 0.05 wt% SWCNTs. The CNT/Al2O3 nanocomposite was pressureless sintered in air using graphite powder as bed powder at 1520 °C for 1 h. The hardnesses and fracture toughnesses were lower than for pure Al2O3 and Al2O3 + 0.1 wt% SWCNTs and Al2O3 + 0.1 wt% MWCNTs. A predominantly transgranular fracture mode with a decrease in crack deflection and no pull-out was observed in the SWCNT + MWCNT–Al2O3 nanocomposite. MWCNTs had to the best reinforcing effect in Al2O3 nanocomposite.  相似文献   

9.
《Materials Research Bulletin》2013,48(11):4723-4728
Self-dopant LaMnO3+δ nanoparticles have been successfully synthesized by metal citrate complex method based on Pechini-type reaction route, at low temperature (773 K). Powder X-ray diffraction and transmission electron microscope revealed pure and nanostructured phase of LaMnO3+δ (δ = 0.125) with an average grain size of ∼72 nm (773 K) and ∼80 nm (1173 K). DC-magnetization measurements under an applied magnetic field of H = ±60 kOe showed an increase in the magnetization with the increase of calcination temperature. Ferromagnetic nature shown by non-stoichiometric LaMnO3+δ was verified by well-defined hysteresis loop with large remanent magnetization (Mr) and coercive field (Hc). Surface areas of LaMnO3+δ nanoparticles were found to be 157.4 and 153 m2 g−1 for the samples annealed at 773 K and 1173 K, respectively.  相似文献   

10.
The photoluminescence (PL) and vacuum ultraviolet (VUV) excitation properties are studied for the BaZr(BO3)2:Eu3+ phosphor with incorporating the Al3+, La3+, or Y3+ ion into the lattice. The excitation spectrum shows an absorption band in the VUV region with the band-edge at 200 nm and a very weak charge transfer band of Eu3+ at about 226 nm. The luminescence spectrum shows a strong emission at 615 nm (5D0  7F2 transition) and weak emission at 594 nm (5D0  7F1 transition) in BaZr(BO3)2:Eu3+, with a good red color purity. The PL intensity is increased by incorporating Al3+ into the BaZr(BO3)2 lattice. The PL intensity has also increased by incorporating La3+ into the lattice, however, the red color purity has deteriorated because of the increased centrosymmetric nature of the site. With the incorporation of Y3+ into the BaZr(BO3)2 lattice, the PL characteristics of the Eu3+ activator resembles that in the YBO3 lattices. The intensity of the red PL for the Eu3+ activator is the highest with good color purity for BaZr(BO3)2:Eu3+ incorporated with both Al3+ (10%) and La3+ (0.5%).  相似文献   

11.
《Materials Research Bulletin》2013,48(11):4729-4732
Novel Er3+/Yb3+ co-doped BaTi2O5–Gd2O3 spherical glasses have been fabricated by aerodynamic levitation method. The thermal stability, upconversion luminescence, and magnetic properties of the present glass have been studied. The glasses show high thermal stability with 763.3 °C of the onset temperature of the glass transition. Red and green emissions centered at 671 nm, 548 nm and 535 nm are obtained at 980 nm excitation. The upconversion is based on a two-photon process by energy transfer, excited-state absorption, and energy back transfer. Yb3+ ions are more than Er3+ ions in the glass, resulting in efficient energy back transfer from Er3+ to Yb3+. So the red emission is stronger than the green emissions. Magnetization curves indicate that magnetic rare earth ions are paramagnetic and the distribution is homogeneous and random in the glass matrix. Aerodynamic levitation method is an efficient way to prepare glasses with homogeneous rare earth ions.  相似文献   

12.
《Materials Letters》2006,60(21-22):2645-2649
The single phases of Y0.95  xMxBO3:5%Eu3+ (M = Ca, Sr, Ba, Zn, Al, 0  x  0.1) were synthesized successfully by solid-state reaction. Their luminescent properties were studied under UV and VUV excitation. The results indicated that with the incorporation of Ca2+, Sr2+, Ba2+, Zn2+ or Al3+ into the host lattice of YBO3:Eu3+, the high symmetry around Eu3+ was destroyed and the ratio of red emission(5D07F2) to orange one (5D07F1) increased, leading to a better chromaticity. Furthermore, the co-doping ions such as Ca2+, Zn2+ and Al3+ were beneficial to enhance the luminescent intensity of Eu3+. These phenomena were evaluated, and possible explanations were proposed.  相似文献   

13.
In this work, the effects of montmorillonite (MMT) dispersion and electron beam irradiation on intercalation and flammability-thermal behaviours of alumina trihydrate (ATH) added low density polyethylene and ethylene vinyl acetate (LDPE–EVA) blends were investigated. MMT and ATH added LDPE–EVA blends were compounded using Brabender mixer and compression moulded into sheets. The samples sheets were electron beam irradiated in the dosage range of 0 to 250 kGy. The dispersion and intercalation of nano-MMT in LDPE–EVA matrix were investigated through X-ray diffraction (XRD) analysis. The d-spacing measurements revealed that the addition of nano-MMT has effectively intercalated into polymer matrix and this has enhanced the compatibility of ATH particles and LDPE–EVA matrix. Limiting oxygen index test (LOI) revealed that the incorporation of MMT into ATH added LDPE–EVA blends as improved the flame retardancy up to 26.5 LOI%. Besides, the application of electron beam irradiation were also improved the flame retardancy of the blends by increasing the LOI% for about 2% compared to non-irradiated samples. The application of irradiation dosage up to 250 kGy has rapidly improved the thermal stability of blends by delaying decomposition temperature and also promoting formation of char. The increasing of MMT loading level and irradiation dosage has effectively enhanced tensile strength and Young’s modulus by intercalating polymer matrix into interlayer galleries of MMT particles. Beside, the formation of crosslinking networks in polymer matrix also could further enhance the tensile strength and Young’s modulus. The intercalation effect of MMT particles and formation of crosslinking networks in polymer matrix could improve the thermal and mechanical properties. Consequently, this study has demonstrated that addition of MMT and electron beam irradiation into ATH added LDPE–EVA blends could produce better flammability, thermal and physical properties of ATH added LDPE–EVA blends.  相似文献   

14.
《Materials Research Bulletin》2006,41(10):1854-1860
The luminescent properties of Sr3Al2O6 doped and co-doped with the rare earths (Ln3+ = Eu3+, Dy3+, Eu3+ and Dy3+) have been studied. The material was synthesized by reflux method and fired up to 900 °C for 16 h. The X-ray diffraction pattern confirms that the synthesized material consists of Sr3Al2O6 as main phase. The photoluminescence study gives a clear evidence of europium stabilizing in trivalent form and surprisingly with no presence of europium in the divalent state. The addition of Dy3+ as co-dopant in the Sr3Al2O6:Eu3+ matrix shows the quenching effect in the photoluminescence (PL) spectra. The photoluminescence intensity of Eu3+ falls gradually on increasing the concentration of the co-dopant in the range from 0.1 mole% to 2.0 mole%. The significantly intense thermoluminescence (TL) glow peak was obtained for Sr3Al2O6:Eu3+, Dy3+ (1% and 0.1%) at around 194 °C when irradiated with 10 kGy dose from Sr-90 β source.  相似文献   

15.
Cr3+:Al2O3 nano-powders were prepared through low-temperature combustion synthesis (LCS) method by using glucose as a dispersion agent for the first time. The Cr3+:Al2O3 nano-powders samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and luminescence spectrometer. XRD results showed that pure α-Al2O3 phase was obtained for the sample fired at 1100 °C for 0.5 h. TEM results indicated that nano-powders were well dispersed. Luminescence spectrum analysis results indicated that the excitation spectrum of Cr3+:Al2O3 nano-powders consisted of two bands peaking at 462 nm and 579 nm, respectively, and the emission spectrum consisted of two bands peaking at 692 nm and 668 nm, respectively.  相似文献   

16.
《Materials Research Bulletin》2013,48(11):4743-4748
We investigate the persistent luminescence in europium-doped strontium pyrophosphate upon codoping with auxiliary rare earth ions. The persistent phosphors are synthesized via solid-state reaction method under flowing N2 + H2. Under UV irradiation, broadband emission persistent luminescence located at 420 nm is observed in all of these phosphors at room temperature. The effects of auxiliary rare earth ions on Sr2P2O7:Eu2+ are discussed according to the decay curves and thermoluminescence spectra. Sr2P2O7:Eu2+,Lu3+ shows the best performance, while and La3+ and Ce3+ codoped samples are the weakest. The influence of auxiliary codopants is discussed in terms of ionic potential and ionic radius. We derive an empirical formula based on the experimental results.  相似文献   

17.
Hybrid nanocomposites fabricated based on an optimized physical and chemical properties modified polypropylene (PP)/polypropylene grafted maleic anhydride (PP-g-MA) with varied concentrations (1–7 wt% at a step of 2 wt%) of organoclay, montmorillonite (MMT). The morphology of the nanocomposites was studied by scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). It was found that partly intercalated and partly exfoliated structure (intercalated–exfoliated structures) existed in the system. The degree of exfoliation is a key factor to determine the reinforcement efficiency. The ratio of exfoliation to intercalation plays an important role in determining the properties of PP nanocomposites and only completely exfoliated silicate layers can significantly improve the properties. PP hybrid nanocomposites showed good thermal stability in the thermogravimetric analysis (TGA). Introduction of ∼3% MMT in the nanocomposites increased the onset temperature of degradation by 27.5 °C compared to that of pure PP, while the 5 wt% MMT resulted the maximum hardness in these nanocomposites. The solvent resistance of PP hybrid nanocomposites slightly increased with increasing the clay content.  相似文献   

18.
Using the coal fly ash (FA), pure-form Na-A and -X zeolites were synthesized by two-step process. The FA was pretreated in aqueous NaOH solution under stirring condition at 85 °C for 18 h. The amorphous aluminosilicate of FA was dissolved during pretreatment. Increasing the stirring speed accelerated the dissolution of FA and increased Si4+ and Al3+ concentrations in the solution. This fact indicated that the stirring during pretreatment significantly affected on the dissolution of FA. After pretreatment, remaining FA was removed and aqueous NaAlO2 solution was added to the residual solution to control the molar ratio SiO2/Al2O3 of 0.5–4.5. After aging the resultant at 85 °C for 24 h, white precipitates were generated over the whole SiO2/Al2O3 range. Increment of Si4+ concentration by stirring during pretreatment increases the yield of the product. At SiO2/Al2O3 = 0.5, the material was identified as Na-A zeolite with a trace amount of hydroxysodalite. A single phase Na-A zeolite was obtained at SiO2/Al2O3 = 1.0. The Na-X zeolite was emerged at SiO2/Al2O3 ? 2.0. At SiO2/Al2O3 = 4.5, a single phase Na-X zeolite was formed. The cation exchange capacity of synthetic single phase Na-A and -X zeolites was respectively 4.78 and 3.88 meq./g.  相似文献   

19.
《Optical Materials》2014,36(12):2053-2055
The comparative study of the luminescent properties of Al2O3:Ti crystal in comparison with those for undoped Al2O3 crystal counterpart is performed under synchrotron radiation excitation with an energy of 3.7–25 eV. Apart from the main emission band peaked at 725 nm related to the 2E  2T2 radiative transitions of Ti3+ ions, the luminescence of excitons localized around Ti ions in the band peaked at 290 nm and the luminescence of F+–Ti and F–Ti centers in the bands peaked at 325 and 434 nm are also found in the emission spectra of Al2O3:Ti crystal. We show also that the luminescence of Ti3+ ions in Al2O3:Ti crystal can be effectively excited by the luminescence of excitons localized around Ti dopant as well as by the luminescence of F–Ti centers.  相似文献   

20.
The effect of titanium additions on the interface and mechanical properties of infiltrated Cu8 wt%Al–Al2O3 composites containing 57 ± 2 vol% ceramic are investigated, exploring two different Al2O3 particle types and four different Ti concentrations (0, 0.2, 1, 2 wt%Ti). Addition of 0.2 wt%Ti leads to the development of a thin (5–10 nm) layer enriched in Ti at the interface between Cu alloy and Al2O3 particles; this Ti concentration produces the best mechanical properties. With higher Ti-contents Ti3(Cu, Al)3O appears; this decreases both the interface and composite strength. Composites reinforced with vapor-grown polygonal alumina particles show superior mechanical properties compared to those reinforced by angular comminuted alumina particles, as has been previously documented for aluminum-based matrices. Micromechanical analysis shows that damage accumulation is more extensive, as is matrix hardening by dislocation emission during composite cooldown, in the present Cu8 wt%Al matrix composites compared with similarly reinforced and processed Al-matrix composites.  相似文献   

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