Incorporation of PbF₂ into Heavy Metal Oxide Borate Glasses. Structural Studies by Solid State NMR

Abstract

A series of heavy metal oxide (HMO) glasses with composition 26.66B 2 O 3 -16GeO 2 -4 Bi 2 O 3 -(53.33-x)PbO-xPbF 2 (0 ≤ x ≤ 40) were prepared and characterized with respect to their bulk (glass transition and crystallization temperatures, densities, molar volumes) and spectroscopic properties. Homogeneous glasses are formed up to x = 30, while crystallization of β-PbF 2 takes place at higher contents. Substitution of PbO by PbF 2 shifts the optical band gap toward higher energies, thereby extending the UV transmission window significantly toward higher frequencies. Raman and infrared absorption spectra can be interpreted in conjunction with published reference data. Using 11 B and 19 F high-resolution solid state NMR as well as 11 B/ 19 F double resonance methodologies, we develop a quantitative structural description of this material. The fraction of four-coordinate boron is found to be moderately higher compared to that in glasses with the same PbO/B 2 O 3 ratios, suggesting some participation of PbF 2 in the network transformation process. This suggestion is confirmed by the 19 F NMR spectra. While the majority of the fluoride ions is present as ionic fluoride, ∼20% of the fluorine inventory acts as a network modifier, resulting in the formation of four-coordinate BO 3/2 F − units. These units can be identified by 19 F{ 11 B} rotational echo double resonance and 11 B{ 19 F} cross-polarization magic angle spinning (CPMAS) data. These results provide the first unambiguous evidence of B−F bonding in a PbF 2 -modified glass system. The majority of the fluoride ions are found in a lead-dominated environment. 19 F− 19 F homonuclear dipolar second moments measured by spin echo decay spectroscopy are quantitatively consistent with a model in which these ions are randomly distributed within the network modifier subdomain consisting of PbO, Bi 2 O 3 , and PbF 2 . This model, which implies both the features of atomic scale mixing with the network former borate species and some degree of fluoride ion clustering, is consistent with all of the experimental data obtained on these glasses.

Fluorophosphate Upconversion-Luminescent Glass-Ceramics Containing Ba2LaF7:Er3+ Nanocrystals: An Advanced Solid-State Nuclear Magnetic Resonance Study

“…Static 19 F spin-echo experiments were conducted to measure the 19 F– 19 F homonuclear dipolar effect. The 90 and 180° pulse lengths are 2.1 and 4.2 μs, respectively.…”

“…The signals were deconvoluted into the Gaussian (for 31 P) and chemical shift anisotropy (CSA) (for 19 F) components employing the DMFIT software. 37 Static 19 F spin-echo experiments 38 were conducted to measure the 19 F− 19 F homonuclear dipolar effect. The 90 and 180°pulse lengths are 2.1 and 4.2 μs, respectively.…”

A comparable study of the EPR spectra and local structures for 3d1‐ and 3d9‐doped halo‐borate glasses

“…Especially in the field of oxide glasses, the thermodynamic model of Shakhmatkin and Vedishcheva has been successfully applied in previous years. [1][2][3][4][5][6][7][8][9] The SVTDM model considers glasses and melts to be an ideal solution formed by salt products of equilibrium chemical reactions of simple starting substances, e.g. oxides, halides, etc.…”

“…[1][2][3] xPbX 2 -PbO-B 2 O 3 glasses (X = F, Cl, and Br; x = 5, 10, 15, 20, and 25 mol%) as a typical representative are well known for their high density, high refractive index, excellent infrared transmission light, nonlinear optics, and superconductivity, which can afford the wide applications in infrared fiber, laser window, multifunctional nonlinear optical devices, and other fields. [4][5][6] These properties can be ascribed to the compositions and intrinsic structure. For example, due to the flexible composition in terms of the BO 3 triangles and BO 4 tetrahedra, of which the amount can be modified by importing PbO and PbX 2 (X = F, Cl, and Br) in the network and thus enhance the transparency in the IR region.…”

Composition–Structure–Property Correlations in Rare-Earth-Doped Heavy Metal Oxyfluoride Glasses

“…Therefore, they are considered to be a good choice as hosts for RE ions in optical materials. − In addition, glasses containing heavy metal oxides, such as Pb, Cd, and Bi oxides, attract special interest owing to their high refractive indexes, low glass-transition temperatures, high polarizabilities, and good dispersal of RE ions . Of particular interest are lead fluorogermanate glasses, which combine these features with high transparency in the range from near-UV to IR (0.35–6 μm) and which offer the prospect of preparing transparent glass ceramics, based on the crystallization of rare-earth doped cubic PbF 2 by controlled thermal annealing. − As substitution of expensive germanium oxide by another network former species would be highly desired for device applications, a large number of studies have been devoted to the preparation, characterization, and crystallization of lead fluoroborate glasses in the system B 2 O 3 –PbO–PbF 2 . − As it is further known that adding the intermediate oxide Al 2 O 3 to oxyfluoride glass formulations has a favorable influence on the thermal, mechanical and chemical stability, the effect of this additive has also been investigated, albeit to a lesser extent. , For further optimization of optical performance characteristics in these glasses, it will be important to establish structure–property correlations, based on suitable spectroscopic probes, such as vibrational spectroscopy, X-ray extended absorption fine structure (EXAFS), and solid-state nuclear magnetic resonance (NMR). In this endeavor, investigating the detailed effects of compositional variation on the spectroscopic signatures of specific structural units and correlating these results with functional performances represent a powerful approach toward these systems.…”