Role of Al Formers and Na Modifers in Al2O3–Sio2–Na2O–Mgo–Eu2O3 Glassess: Brillouin and Raman Spectroscopy Studies (original) (raw)
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Experimental and theoretical studies of Dy3+ doped alkaline earth aluminosilicate glasses
Journal of Luminescence, 2019
Several investigations on rare earth (Sm 3+ , Eu 3+ , Tb 3+) doped aluminosilicate glasses in the last few years showed strong changes in the luminescence properties in dependence on the type and concentration of the network modifier ions. In this article Dy 3+-doped alkaline earth aluminosilicate glasses of the molar composition 35 MO • 10 Al 2 O 3 • 55 SiO 2 (M=Ba, Sr, Ca and Mg) were prepared by using the melt quenching technique. Differential scanning calorimetry (DSC) measurements of these glasses were carried out. Direct and indirect optical band gaps were calculated based on the glasses UV absorption spectra. The Judd-Ofelt (J-O) theory was used to evaluate the three intensity parameters from the experimental oscillator strengths. Using the J-O intensity parameters, several radiative properties such as spontaneous transition probabilities (A R), radiative branching ratios (β R) and radiative lifetimes (τ R) were determined. The photoluminescence spectra obtained by the excitation wavelength of 349 nm show three emission bands at 482 (blue), 574 (yellow) and 660 nm (red) corresponding to the 4 F 9/2 → 6 H (15/2, 13/2, 11/2) transitions, respectively. From the visible emission spectra yellow to blue (Y/B) intensity ratios and chromaticity coordinates were calculated. In the investigated glasses the Y/B ratio is systematically increased with increasing size of the network modifier ions. The lifetimes of the 4 F 9/2 metastable state were also measured. All properties are discussed in relation to the effect of the different network modifier ions on the structure of the glasses and compared to literature data.
Raman, 27 Al and 29 Si NMR spectroscopies are used to investigate the structure of [0.15Na 2 O-0.12MgO-0.03Al 2 O 3-0.70SiO 2 ] ð100ÀxÞ : [Eu 2 O 3 ] x glasses with varying Eu 2 O 3 content (x ¼ 0, 0.73, 1.26, 3.90, 5.26 and 8.11 mol%). Spectral changes in the Raman envelope at (900-1240) cm À1 indicate that the number of silica tetrahedra with more than one non-bridging oxygen (NBO) per tetrahedron and the number of silica tetrahedra with one NBO associated with Eu increase with increasing rare-earth concentration. 29 Si MAS NMR spectra show a single broad peak with maxima at frequencies attributable to a predominance of Q 3 species. Quantitative 27 Al and 29 Si NMR spectroscopies show that aluminum and silicon species become less observable as Eu 2 O 3 content increases, presumably due to interactions with paramagnetic europium. The 27 Al NMR spectra reveal the presence of only tetrahedrally coordinated Al sites, with a gradual increase in the structural disorder associated with these sites as the concentration of Eu 2 O 3 increases. This is in agreement with the appearance of the broad Raman band at 790 cm À1 attributed to Al-O stretching vibrations with Al in fourfold coordination.
Optical and structural investigation on rare-earth-doped aluminophosphate glasses
Optical Materials, 2006
Aluminophosphate glasses belonging to the oxide system Li 2 O-BaO-Al 2 O 3 -La 2 O 3 -P 2 O 5, un-doped and doped with rare-earth metal ions (Ce 4+ , Nd 3+ , Sm 3+ ) were obtained by a wet non-conventional method. The influence of the doping ions on the optical properties of the phosphate glasses has been investigated in relation with structural features of the vitreous matrix. The optical behavior has been studied by ultra-violet-visible-near-infra-red (UV-VIS-NIR) spectroscopy, revealing electronic transitions specific for rare-earth ions. Structural information via optical phonons was provided by infrared (IR) absorption spectra in the range 400-4000 cm À1 . Raman and fluorescence spectroscopy measurements have been performed. A strong fluorescence was observed in the visible spectrum, using 514.5 nm and 633 nm laser excitation.
Characterization of rare earth aluminosilicate glasses
Journal of Non-Crystalline Solids, 2005
Rare earth glasses are commonly used in lasers, sensors and radiation shield glasses. Rare earth aluminosilicate-based glasses have been successfully used as in vivo radiation delivery vehicles, in treatment of primary hepatocellular carcinoma, irradiation of diseased synovial membrane for the treatment of rheumatoid arthritis, and treatment of prostate tumors. These glasses have also been found useful to promote liquid-phase sintering of covalent ceramics and, specifically, silicon carbide-based ceramics. Usually, the SiO 2 -Al 2 O 3 -RE 2 O 3 system is used as sintering additives. In this work, several rare earth silicate glasses (RE = Y, La, Nd, Dy and Yb) were prepared based on 60%SiO 2 -20%Al 2 O 3 -20%RE 2 O 3 (mol%) compositions. These glasses were characterized by infrared spectroscopy and nuclear magnetic resonance. Moreover, the liquid phase sintering of silicon carbide ceramics was studied using dilatometric experiments with 10 vol.% additives of the 60%SiO 2 -20%Al 2 O 3 -20%RE 2 O 3 system.
2011
systems. The density, molar volume, compactness, Vickers hardness, refractive index, as well as the glass transition (T g ) and crystallization temperature are compared for two series of RE-Al-Si-O (RE 5 La, Y, Lu, Sc) glasses that display a constant molar ratio n Al /n Si 5 1.00, whereas n RE /n Si is equal to either 0.62 or 0.94. Several glass properties scale roughly linearly with the cation field strength (CFS) of the rare-earth (RE 31 ) ion, except for the T g values of the Sc-bearing glasses that are significantly lower than expected. Magic-angle spinning 29 Si and 27 Al nuclear magnetic resonance (NMR) reveal enhanced network disorder and increased relative populations of AlO 5 and AlO 6 polyhedra in the aluminosilicate glasses for increasing RE 31 CFS, but overall similar Si and Al local environments (chemical shifts and quadrupolar couplings) in all samples associated with a constant n RE /n Si ratio, except for unexpectedly shielded 29 Si NMR signals observed from the Sc-Al-Si-O glasses.
The Journal of Physical Chemistry C, 2012
By combining molecular dynamics (MD) simulations with 29 Si and 27 Al magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy, we present a comprehensive structural report on rare-earth (RE) aluminosilicate (AS) glasses of the RE 2 O 3 −Al 2 O 3 −SiO 2 (RE = Y, Lu) systems, where the latter is studied for the first time. The structural variations stemming from changes in the glass composition within each RE systemas well as the effects of the increased cation field-strength (CFS) of Lu 3+ relative to Y 3+ are explored and correlated to measured physical properties, such as density, molar volume, glass transition temperature, and Vickers hardness (H V). 29 Si NMR reveals a pronounced network ordering for an increase in either the RE or Al content of the glass. Al mainly assumes tetrahedral coordination, but significant AlO 5 and AlO 6 populations are present in all structures, with elevated amounts in the Lu-bearing glasses compared to their Y analogues. The MD-derived oxygen speciation comprises up to 3% of free O 2− ions, as well as non-negligible amounts (4−19%) of O [3] coordinations ("oxygen triclusters"). While the SiO 4 groups mainly accommodate the nonbridging oxygen ions, a significant fraction thereof is located at the AlO 4 tetrahedra, in contrast to the scenario of analogous alkali-and alkaline-earth metal-based AS glasses. The average coordination numbers (CNs) of Al and RE progressively increase for decreasing Si content of the glass, with the average CN of the RE 3+ ions depending linearly on both the amount of Si and the fraction of AlO 5 groups in the structure. The Vickers hardness correlates strongly with the average CN of Al, in turn dictated by the CFS and content of the RE 3+ ions. This is to our knowledge the first structural rationalization of the well-known compositional dependence of H V in RE bearing AS glasses.
Influence of Small Additions of Al2O3 on the Properties of the Na2O⊙ 3SiO2 Glass
Changes in the structural properties of sodium alumino-silicate glasses of general formula Na 2 O‚xAl 2 O 3 ‚(3x)SiO 2 were investigated as a function of Al 2 O 3 concentration. The experimental evidences provided by density, elastic modulus, glass chemical resistance measures, 29 Si and 27 Al MAS NMR investigations were complemented by molecular dynamics simulations. While neither of the experimental techniques or computational investigation utilized in this study were able to furnish unequivocable responses for the rationalization of the measured properties of sodium alumino-silicate glasses, the synergistic application of experimental and computational techniques showed that the anomalies observed in bulk properties like density and elastic modulus find their origin in medium-range structural features.
2011
A rare-earth rich aluminoborosilicate glass of composition (given in wt.%): 50.68 SiO 2 -4.25 (where M and M' are respectively an alkali and alkaline earth cation) is currently under study as potential nuclear waste form. In this work, we were interested in the structure of this glass in relation with the modifier cation type. Two different glass series were elaborated by changing separately the nature of the alkaline (M=Li, Na, K, Rb, Cs) and the alkaline-earth (M'=Mg, Ca, Sr, Ba) ions and different structural studies were intended to elucidate the local environment of the rare-earth and the network arrangement. Only slight effect was put in evidence on the covalency degree and the length of Nd-O linkage with a change of M or M', by optical spectroscopy and EXAFS measurements. Raman and MAS NMR ( 29 Si, 27 Al, 11 B) spectroscopies showed a variation of the polymerization degree of the network with the size of the modifier cation. Finally, the most important feature of this glass composition is related to the AlO 4 charge compensation which was proved to be uniquely assured by alkali cations.
Materials, 2018
The medium-range atomic structure of magnesium and barium aluminosilicate glasses doped with Gd2O3 as a model rare earth oxide is elucidated using molecular dynamics simulations. Our structure models rationalize the strong dependence of the luminescence properties of the glasses on their chemical composition. The simulation procedure used samples’ atomic configurations, the so-called inherent structures, characterizing configurations of the liquid state slightly above the glass transition temperature. This yields medium-range atomic structures of network former and modifier ions in good agreement with structure predictions using standard simulated annealing procedures. However, the generation of a large set of inherent structures allows a statistical sampling of the medium-range order of Gd3+ ions with less computational effort compared to the simulated annealing approach. It is found that the number of Si-bound non-bridging oxygen in the vicinity of Gd3+ considerably increases with...
NMR Study of a Rare-Earth Aluminoborosilicate Glass with Varying CaO-to-Na2O Ratio
Applied Magnetic Resonance, 2007
The effect of substituting two Na ! by one Ca 2! in a rare-earth aluminoborosilicate glass is investigated by multinuclear magic-angle spinning (MAS) and multiple-quantum (MQ)MAS nuclear magnetic resonance (NMR) spectroscopy. Quantitative analysis of the 23 Na and 27 Al MAS/MQMAS data along with the 11 B MAS NMR data provides complementary information enabling to cast light on different structural key points. A strong decrease of the N 4 " BO 4 /(BO 3 ! BO 4 ) ratio is observed consecutively to this substitution, indicating that sodium is more favorable than calcium to the formation of BO 4 units. The experimental N 4 ratio is compared to the Dell and Bray model prediction and it is shown that several adjustments, due to the presence in our glass of Nd and Zr, are necessary to obtain acceptable agreement with experimental data. 29 Si MAS NMR data also put in evidence an effect of the substitution on the polymerization degree. Glass in glass phase separation is clearly detected when the ratio of CaO to Na 2 O is greater than 1 and a different evolution of NMR parameters is observed for the ratio of CaO to Na 2 O being less than or equal to 1. Concerning aluminum charge compensation, it is demonstrated that, as long as no phase separation is detected, the negative charge of AlO 4 # entities is almost exclusively balanced by sodium cations. Finally, changes of the sodium ions organization within the glass network are also evidenced by spinlattice relaxation and spin echo decay measurements.