共查询到20条相似文献,搜索用时 31 毫秒
1.
Shimin Liu Gaoling Zhao Wangle Ruan Zhiwang Yao Tingting Xie Ji Jin Hao Ying Jianxun Wang Gaorong Han 《Journal of the American Ceramic Society》2008,91(8):2740-2742
Eu2 O3 -doped aluminoborosilicate glasses were prepared in air at high temperature. Luminescence measurements were used to investigate a valence change from Eu3+ to Eu2+ ions in the aluminoborosilicate glasses. The results showed that the doped Eu3+ ions were partially reduced to Eu2+ in the Eu2 O3 :RO–Al2 O3 –B2 O3 –SiO2 (RO=CaO, SrO, BaO, Li2 O) glasses, but not in the Eu2 O3 :RO–Al2 O3 –B2 O3 –SiO2 (RO=Na2 O, K2 O) glasses. The changes of Eu reduction with different RO components were discussed with the variation of optical basicity of RO and with different valency of R cations. The effects of co-doping BaO and ZnO in aluminoborosilicate glasses on Eu reduction were also investigated and discussed. 相似文献
2.
Jie Fu 《Journal of the American Ceramic Society》2000,83(10):2613-2615
Transparent surface-crystallized glass-ceramics with molar compositions of 43SiO2 –2B2 O3 –30SrO–25MgO–0.05Eu2 O3 –0.8Dy2 O3 (sample GC-A) and 43SiO2 –2B2 O3 –24SrO–6CaO–25MgO–0.05Eu2 O3 –0.8Dy2 O3 (sample GC-B) were prepared by heat-treating the mother glasses at 850°C for 10 h. The precipitated phases in both glass-ceramics were (Sr1− x Ca x )2 MgSi2 O7 , in which Eu2+ and Dy3+ ions were incorporated. Phosphorescence with emission peaks at 470 and 480 nm that is due to the 4 f 6 5 d –4 f 7 transition of Eu2+ ions was observed from samples GC-A and GC-B, respectively. The phosphorescence lasted for >5 h at room temperature. 相似文献
3.
Anal Tarafder Kalyandurg Annapurna Reenamoni Saikia Chaliha Vidya Sagar Tiwari Pradeep Kumar Gupta Basudeb Karmakar 《Journal of the American Ceramic Society》2009,92(9):1934-1939
We report here the processing and properties of transparent glass and glass–ceramic nanocomposites in the Li2 O–Ta2 O5 –SiO2 –Al2 O3 system in the presence of Eu2 O3 as luminescent probe. The formation of the LiTaO3 crystal phase, the crystallite size, and the morphology with the progression of heat treatment have been examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transformed infrared reflectance spectroscopy measurements. The crystallite sizes obtained from XRD and TEM are found to increase with heat-treatment time and vary in the range of 2–20 nm. The measured photoluminescence spectra exhibit emission transitions of 5 D0,1 →7 F j ( j =0, 1, 2, 3, and 4) of Eu3+ ions. From the nature of the emission transitions, the site symmetry in the vicinity of Eu3+ ions has been found to be near C3v in the glass–ceramic nanocomposites. An inverse correlation has been observed between the asymmetric ratio ( I ED / I MD ) of Eu3+ ions and the dielectric constant (ɛr ), with an increase in the heat-treatment time of glass, which is caused by the dipole–dipole interaction. 相似文献
4.
Daijitsu Harada Yukio Hinatsu Nobuyuki Masaki Akio Nakamura 《Journal of the American Ceramic Society》2002,85(3):647-652
Powder X-ray diffractometry (XRD) and 151 Eu Mössbauer spectroscopy were performed for samples prepared in the temperature range 1500–1500°C for the hafnia–europia (HfO2 –Eu2 O3 ) system Eu x Hf1− x O2− x /2 (0 ≤ x ≤ 1.0). The XRD results showed that two types of solid solution phases formed in the composition range 0.25 ≤ x ≤ 0.725: an ordered pyrochlore-type phase in the middle-composition range (0.45 < x < 0.575) and a disordered fluorite-type phase, enveloping the pyrochlore-type phase on both sides, in the composition ranges 0.25 ≤ x ≤ 0.40 and 0.60 ≤ x ≤ 0.725. 151 Eu Mössbauer spectroscopy sensitively probes local environmental changes around trivalent europium (Eu3+ ) caused by the formation of these solid solution phases. In addition to the broad, single Mössbauer spectra observed in this study for the Eu3+ , the values of isomer shift (IS) exhibited a pronounced minimum in the neighborhood of the stoichiometric pyrochlore phase ( x ≈ 0.5). Such IS behavior of Eu3+ was interpreted based on the XRD crystallographic information that the ordered pyrochlore phase has a longer (in fact, the longest) average Eu–O bond length than those of the disordered fluorite phases on both sides or the monoclinic (and C-type) Eu2 O3 at x = 1.0. 相似文献
5.
Koji Fujita Katsuhisa Tanaka Kazuyuki Hirao Naohiro Soga 《Journal of the American Ceramic Society》1998,81(7):1845-1851
Borate glasses containing 0.99–30.0 mol% EuO have been prepared under a reducing atmosphere and 151 Eu Mössbauer effect measurements have been carried out at room temperature in order to examine the chemical state of Eu2+ ions in these glasses. Mössbauer spectra indicate that most of the europium ions are present as the divalent oxidation state. In dilute Eu2+ -containing borate glasses, spectra are split due to paramagnetic hyperfine interactions in the glasses with low and high sodium contents. In concentrated Eu2+ -containing borate glasses, line broadening results from the contribution of quadrupole splitting due to asymmetrical oxygen coordination around Eu2+ and the contribution of inhomogeneous broadening due to site-to-site variation. The compositional dependence of isomer shift and quadrupole interaction parameter can be related to the structural changes in the borate glass. The variation of the isomer shift has a good correlation with the optical basicity of glass, and the trend can be explained in terms of the covalent admixture with 6 s character. The Eu-O bond in the borate glasses is more ionic than that in EuTiO3 and EuZrO3 , where the oxygen coordination number for Eu2+ is 12. The average coordination number for Eu2+ is found to be 12 in all of the present glasses. 相似文献
6.
A large glass-forming region was discovered in the system EUO–Al2 O3 –B2 O3 and chemically stable glasses of good optical quality were produced. The concentration range extends from about 3 to 43 mole % EuO. Room-temperature Verdet constants as large as –2.55 min/oe-cm were measured on a glass containing 30.5 mole % Eu2+ . This is somewhat higher than those reported for the trivalent rare-earth ions in similar glass matrices. The effective transition wavelength causing the rotation is 380 ± 20 mμ. Compared to Ce3+ , Tb3+ , and Pr3+ the large rotation of Eu2+ in the visible region is due primarily to a large J (total angular momentum) value as well as to a large effective transition wavelength. 相似文献
7.
Doo-Hee Cho Kazuyuki Hirao Koji Fujita Naohiro Soga 《Journal of the American Ceramic Society》1996,79(2):327-332
Photochemical hole burning (PHB) not only can be applied for data storage systems but also serves as a powerful method for studying the local structure around optical centers. The present work investigated the effects of aluminum, magnesium, and silicon ions on hole burning and the phonon sideband for borate glasses that exhibit PHB at room temperature. Hole burning was measured for the 5 D 0−7 F 0 transition of Sm2+ and the phonon sideband spectrum for the 5 D 0 -7 F 0 transition of Eu3+ . The hole width was closely related to local structural change, especially as it seemed to decrease with decreases in the number of nonbridging oxygens produced around the rare-earth ions. In the case of sodium aluminoborate glasses, the hole width decreased considerably with increasing alumina content. The ratio Γih /Γh for 85B2 O3·10Al2 O3 ·5Na2 O·1Sm2 O3 glass, then, was 80 at room temperature, the largest value ever reported. 相似文献
8.
Masayuki Nogami Naoya Hayakawa Naoya Sugioka Yoshihiro Abe 《Journal of the American Ceramic Society》1996,79(5):1257-1261
Samarium ions (Sm2+ ) incorporated into aluminosilicate glasses by a sol-gel process showed persistent spectral hole burning at room temperature. Gels of the system Na2 O-Al2 O3 SiO2 synthesized by the hydrolysis of Si(OC2 H5 )4 , Al(OC4 H9 )3 , CH3 COONa, and SmCl3 ·6H2 O were heated in air at 500°C, then reacted with H2 gas to form Sm2+ ions. Whereas Al3+ ions effectively dispersed the Sm3+ ions in the glass structure, Na+ ions were not effective. The Al2 O3 -SiO2 glasses proved appropriate for reacting the Sm3+ ions with H2 gas and exhibited the intense photoluminescence of Sm2+ ions. The reaction of Sm3+ ions with H2 in the Al2 O2 -SiO2 glasses was determined by first-order kinetics, and the activation energy equaled 95 kJ/mol. At 800°C, the maximum photoluminescence of the Sm2+ ions was achieved within 20 min. 相似文献
9.
EzzEldin Metwalli Richard K. Brow Frederick S. Stover 《Journal of the American Ceramic Society》2001,84(5):1025-1032
Alkali aluminophosphate glasses, including those in the system x Al2 O3 ·(1− x )CsPO3 (0 ≤ x ≤ 0.25), were examined by high-performance liquid chromatography (HPLC), infrared (IR), and 27 Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies. Phosphate anions become progressively shorter with the addition of alumina to a metaphosphate glass. Al3+ ions are initially incorporated into the structure in octahedral sites, but the average Al coordination number (CN) decreases with increasing alumina content and tetrahedral species are the preferred moiety when [O]/[P] > 3.5. Al[4] sites appear to be associated with monophosphate (Q0 ) anions. The role of modifier size on aluminophosphate structure is investigated. At low alumina content (<15 mol%), the disproportionation of pyrophosphate anions into triphosphate and orthophosphate anions is responsible for the lower average Al CN of cesium aluminophosphate glasses compared with sodium aluminophosphate glasses. 相似文献
10.
Elastic moduli and fracture toughness were determined for several glasses in the systems soda-alumina-silica, calcia-alumina-silica, and soda-boric oxide-silica. Results for the aluminosilicates are analyzed in terms of Al3+ :Na+ ratios. The mechanical properties do not show maxima or minima at the Al3+ :Na+ ratio of 1, in contrast to conductivity, helium permeability, and refractive index. The moduli and toughness increase with Al3+ :Na+ ratio, which is consistent with increased coherency of the glass network. Glasses which contain B2 O3 instead of Al2 O3 have slightly higher moduli but are considerably tougher. The moduli of calcium aluminosilicate glasses are ∼25% greater than sodium aluminosilicates, whereas the fracture toughnesses are similar. 相似文献
11.
Crystal Chemistry of Hydrous Calcium Silicates: I, Substitution of Aluminum in Lattice of Tobermorite 总被引:1,自引:0,他引:1
GEORGE L. KALOUSEK 《Journal of the American Ceramic Society》1957,40(3):74-80
Mixtures of 0.8 moles of CaO per mole of SiO2 plus Al2 O3 were prepared from lime, kaolin, and tripoli (microcrystalline quartz); the amounts of SiO2 to Al2 O3 were varied to give from 0.2 to 20.7% Al2 O3 by weight of dry solids. After hydrothermal treatment (170° to 175°C.), the products were examined by differential thermal analysis and by X-ray diffraction. A homogeneous solid identified as the mineral tobermorite (4CaO.5SiO2 .5H2 O) and containing up to 4 or 5% Al2 O3 was obtained. Increasing the amount of Al2 O3 in the raw mixture above about 5% resulted in the formation of the hydrogarnet 3CaO.Al2 O3 .SiO2 .4H2 O as a second phase. Allowing for the Al2 O3 combined in this solid, it was indicated that slightly more Al2 O3 was substituted in the tobermorite as the amount was increased in the raw mixture. It is suggested that the Al3+ ions probably assume tetrahedral coordination when substituting for the Si4+ ions. 相似文献
12.
A molecular dynamic simulation was performed for sodium borate glasses containing a small amount of Eu2 O3 to investigate the local structures of cations in glass. A new potential VB-B in the form -A exp[-C(r - 0.239)2 ] was added to the regular modified Born-Mayer-Huggins-type potentials, ΦB-B , ΦB-O , and ΦO-O, to account for the directional tendency of the borate network structure. With this potential added, both the radial distribution of sodium borate glasses observed by small-angle X-ray diffraction and the change in coordination number of boron with sodium content obtained by NMR agreed well with the simulation. The average coordination number of Ed3+ ions in the simulated glasses varied from 7.5 to 8.6, depending on the composition of the host sodium borate glasses. The inhomogeneous line width of the 5 D0 -7 Fz emission peak also changed, depending on the sodium content, with a maximum at 18 mol% Naz O content; this result agrees well with experimental data obtained from laser-induced fluorescence spectra. 相似文献
13.
The coordination of aluminum ions in tricalcium aluminate (3CaO·Al2 O3 ) was examined using infrared absorption, X-ray emission spectroscopy, and molar refraction techniques. Each of these methods indicated the presence of aluminum in fourfold coordination. No evidence was found for aluminum in sixfold coordination. The isomorphous substitution of Sr2+ for Ca2+ and Ga3+ for Al3+ and a comparison between the absorption frequencies for an SiO4 group and an AlO4 group were used to identify the infrared absorption bands in tricalcium aluminate. 相似文献
14.
Spectroscopic properties and local structure of Eu3+ in Ge–Ga–S–CsBr (or CsCl) glasses were investigated using fluorescence measurements and several spectroscopic methods. Fluorescence from Eu3+ :5 D0 →7 F2 was observed only from glasses with CsBr/Ga ratios greater than unity and disappeared at temperatures above 140 K. Phonon sideband (PSB) spectra revealed that Eu3+ ions are located next to halogen ions, which form part of well-structured complexes such as EuCl3 , tetrahedral [GaS3/2 Cl]− , subunits and/or Ga2 Cl6 . These new bonds showed reduced coupling strength compared with Eu3+ –S bonds in Ge–Ga–S glass. Fluorescence line narrowing experiments showed little site-to-site variation of Eu3+ ions. 相似文献
15.
Eun Jin Kim Sung-Woo Choi Seong-Hyeon Hong 《Journal of the American Ceramic Society》2007,90(9):2795-2798
Eu3+ -doped (1–12 mol%) calcium hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) powders were synthesized by a precipitation method and their photoluminescence (PL) properties were investigated. Eu has a limited solubility in HA and Eu2 O3 was detected by X-ray diffraction above 3% doping, whereas a nearly single β-phase was obtained up to 6% doping in TCP but EuPO4 appeared in the 12% Eu-doped specimen. Electron spin resonance measurement confirmed that europium ions exist as Eu3+ in both samples. Eu3+ -doped HA exhibited a strong emission at 575 nm with several minor peaks at 610–640 nm and Eu3+ -doped TCP had an intense emission at 613 nm with secondary peaks at 590–600 nm, which were consistent with the earlier reports determined at low temperatures. In Eu-doped TCP, the PL intensity increased with increasing calcination temperature without phase transformation. The more the Eu added, the higher the PL intensity obtained in both cases. 相似文献
16.
HOWARD V. LAUER Jr. RICHARD V. MORRIS 《Journal of the American Ceramic Society》1977,60(9-10):443-451
Experimental studies were made on the compositional dependence of the redox equilibrium of Eu in synthetic silicate liquids, together with an empirical model describing the observed compositional dependence. Electron paramagnetic resonance (EPR) was used to measure the concentration ratio of Eu2+ to Eu3+ in various glasses formed by rapidly quenching silicate liquids. The compositional field studied comprised mixtures of SiO2 , TiO2 , Al2 O3 , CaO, MgO, and Na2 O. The proposed model describes the Eu2+ /Eu3+ ratio over the entire compositional field in terms of parameters easily related to each glass composition. The general applicability and utility of the model is further demonstrated by its application to the Fe2+ -Fe3+ , Ce3+ -Ce4+ , and Cr3+ -Cr6+ redox reactions in binary alkali oxide silicate glasses of Li, Na, and K. 相似文献
17.
Shankar Krishnan J. Richard K. Weber Stuart Ansell April D. Hixson Paul C. Nordine 《Journal of the American Ceramic Society》2000,83(11):2777-2780
We report the first measurements of the structure factor, S ( Q ), and the pair distribution function, G ( r ), of Al6 Si2 O13 (3:2 mullite) in the normal and supercooled liquid states in the temperature range 1776–2203 K. Measurements are obtained by synchrotron X-ray scattering on levitated, laser-heated liquid specimens. The S ( Q ) shows a prepeak at 2.0 Å−1 followed by a main peak at 4.5 Å−1 and a weak feature at 8 Å−1 . The G ( r ) shows a strong (Si,Al)–O correlation at 1.80 Å at high temperature that moves to 1.72 Å as the liquid is supercooled. The second and third nearest neighbor peaks at 3.0 and 4.25 Å sharpen with supercooling. The short-range structure of the high-temperature liquid is similar to the corresponding glasses produced by rapid quenching. Supercooling causes an increase in the concentration of tetrahedral Si4+ ions, which is manifested by the large shift in the first peak to lower ionic distance, r , values in G ( r ). The increase in tetrahedrally coordinated Si4+ ions is offset by an increase in octahedral Al3+ ions. The clustering of the SiO4 4− tetrahedral units results in increased viscosity of the liquid at temperatures below the melting point, which is consistent with Al6 Si2 O13 being a fragile liquid. 相似文献
18.
The rate of formation of NiAl2 O4 by reaction between single crystals of NiO and Al2 O3 can be described by k = 1.1 × 104 exp (−108,000 ± 5,000/ RT ) cm2 /s. In NiO the behavior of D as a function of concentration supports the Lidiard theory of diffusion by impurity-vacancy pairs. A good fit of the theory to the experimental results was obtained by assuming that Al3+ ions diffuse as [AlNi · VNi ]'pairs. The diffusion coefficient of pairs, Dp , obeys the equation 6.6 × 10−2 exp (−54,000 ± 3,000/ RT ) cm2 /s. The free energy of association for pairs was calculated to range from 6.5 kcal/mol at 1789°C to 9.0 kcal/mol at 1540°C. The interdiffusion coefficients in the spinel showed a constant small increase with increasing concentration of Al3+ dissolved in the spinel. 相似文献
19.
Interdiffusion coefficients in single-crystal MgO were determined using an MgO-MgAl2 O4 diffusion couple. For a concentration of 1 mol% Al2 O3 in MgO, the interdiffusion coefficient can be expressed as D =2.0±0.2 exp (−76,000±3,000/ RT ) for the MgO-MgAl2 O4 couple. This relation compares well with previous measurements in the MgO-Al2 O3 system. The interdiffusion coefficients, which increased with the mol fraction of cation vacancies, were in the range of 10−8 to 10−10 cm2 s−1 for the concentrations and temperatures studied. Diffusion was enhanced below 1640°C if powdered MgAl2 O4 was used. Self-diffusion coefficients for Al3+ ions in MgO were calculated; Al3+ diffuses faster than Cr3+ in MgO. 相似文献
20.
Emission properties and energy transfer of PbO–Bi2 O3 –Ga2 O3 –GeO2 glasses codoped with Tm3+ and Tb3+ ions were investigated. The 1.48-μm emission due to the Tm3+ :3 H4 →3 F4 transition can be used to amplify the S-band (1460–1530-nm) signal light. With Tb3+ addition, the lifetime and emission intensity of the Tm3+ :3 F4 level decreased sharply via the Tm3+ :3 F4 →Tb3+ :7 F0,1,2 energy transfer. Population densities of the 3 F4 and 3 H4 levels in Tm3+ calculated from rate equations clearly verified that population inversion in Tm3+ ions became possible with as little as 0.1 mol% of Tb3+ addition. 相似文献