The average electronic polarizability of the oxide ion αO2−(no) of numerous binary oxide glasses (phosphate, borate, silicate, germanate, tellurite and titanate) has been estimated on the basis of the refractive index reported in literature. An optical basicity scale has been proposed on the basis of a good agreement between calculated theoretical optical basicity Λth and refractive index based optical basicity Λ(no) of the glasses. It was established that third-order non-linear optical susceptibility χ(3) of the glasses, also found in the literature, increases with increasing optical basicity and tendency for metallization of the glasses. This is associated with the high electron donor ability of the oxide ions and the small optical band gap. Conventional oxide glasses with low refractive index possess low polarizability, low optical basicity, large metallization criterion and small χ(3). Tellurite and titanate glasses as well as borate glasses containing a large amount of Sb2O3 and Bi2O3 with high refractive index above 2.0 show large polarizability, high optical basicity, small metallization criterion and large χ(3).

Electronic polarizability, optical basicity and non-linear optical properties of oxide glasses

Research in borate glasses has started as a scientific curiosity and as an aid to explain the structure of oxide glasses in general. This effort led to a better understanding of the structure and unique properties of borate glasses. Although silicate and borosilicate glasses satisfy the vast majority of scientific and industrial needs, there are certain circumstances where they are not satisfactory. Furthermore, borate glasses offer certain advantages over silicate glasses which are not well known, neither well explored. However, certain characteristics of borate glasses such as their affinity to water requires that they are well selected, designed, or developed to satisfy the specifications of a given application. This review aims to explore and report some of the key properties of binary borate glasses. It also provides certain guidelines for several applications where the scientific literature is discussed in connection with industrial experience and technological needs.

Borate glasses for scientific and industrial applications: a review

Raman spectroscopy was applied to complex sodium alumino-borosilicate glasses that precipitate nepheline as their primary phase. The main focus was on the Raman band at 850 cm−1 (wavenumber) observed in quenched glasses. Based on the literature, the 850 cm−1 band was assigned to AlIV–O–Si units in which tetrahedral AlIV are substituted for Si in the network, creating [AlO4/2]− anions that are charge-balanced by Na+ cations. The same glasses with various temperature histories were examined with optical microscopy, scanning electron microcopy and transmission electronic microscopy. The results indicated that the 850 cm−1 Raman band was associated with nanocrystals that formed in the melts and were preserved in the quenched samples. The chemistry of these nanocrystals resembled nepheline. Models relating the intensity of the Raman band at 850 cm−1 and the liquidus temperature (TL) to glass composition revealed that a relationship exists between these two properties. An increase in B2O3 and SiO2 decreased the Raman band intensity and the TL, whereas an increase in Al2O3 and Na2O increased both properties. These effects were attributed to the influence of various oxides on the Na+–[AlO4/2]− activity in the melt.

Effects of Al2O3, B2O3, Na2O, and SiO2 on nepheline formation in borosilicate glasses: chemical and physical correlations

The electronic polarizability and optical basicity of La2O3 and related glasses have been determined from ultraviolet absorption spectra and calculations based on the Lorentz–Lorenz equation The optical basicity for La2O3 oxide is found to be 107, being much larger compared with typical glass-forming oxides such as B2O3 (042) and SiO2 (048) but being similar to heavy element oxides such as TeO2 (093) The Yamashita and Kurosawa’s interaction parameter of La2O3 is 003 A−3, indicating that La2O3 is classified as a normal ionic (basic) oxide, ie, an ionic bonding character in the La3+–O bond is proposed Close correlations are confirmed among optical basicity, interaction parameter, and oxygen 1s binding energy in x-ray photoelectron (XPS) spectra for La2O3–P2O5 and other La2O3-containing glasses It is found from XPS and Raman spectra that La3+ ions in La2O3–P2O5 glasses act as network modifiers, supporting an ionic bonding character in the La3+–O bond The parameters related to electronic polarizability in La2O3 determined in the present study would be useful for the design of rare-earth containing optical functional glasses

Electronic polarizability, optical basicity, and interaction parameter of La2O3 and related glasses

A Raman spectroscopy study was performed on a series of sodium-aluminoborosilicate glasses with Gd2O3 from 0 mass% up to its solubility (47 mass% or 13.58 mol%). Experimentally measured spectra were fitted with a Gaussian function for each individual band without any restriction on the band position, width, and intensity. The evolution of the spectroscopic bands appears to result from partitioning of the rare earth cation, as its dissolution mechanism, in these borosilicate glasses. Specifically, the evolution of the Raman bands was correlated well with Gd cations partitioning in the borate-rich environment at low Gd2O3 concentration, Gd2O3/[1/3B2O3] 1. Raman bands near 1420 and 710 cm −1 suggest the presence of a local Gd-metaborate environment, which appeared to occur at all Gd2O3 concentrations. The bands near 300 and 910 cm −1 further suggest the formation of Gd–O–Gd clusters in the silicate-rich environment at high Gd2O3 concentrations.

Raman spectroscopic study of gadolinium(III) in sodium-aluminoborosilicate glasses

The third–order nonlinear optical susceptibility, χ(3), of lanthanide (lanthanum, praseodymium, neodymium, and samarium) borate glasses has been measured by the third harmonic generation method. The structure of the present glass system has been studied by infrared and Raman spectroscopic methods. The network structures of the present Ln2O3–B2O3 glasses have been confirmed to be basically similar to each other. Praseodymium, neodymium, and samarium borate glasses exhibit χ(3) values that are larger than lanthanum borate glasses, because of the optical resonance effect, in accordance with the f–f transition. Especially, the χ(3) value for 30Pr2O3·70B2O3 glass is 1.8 × 10−12 esu, which is a factor of ∼60 larger than that of SiO2 glass. This striking enhancement of χ(3) is mainly attributed to the large transition moment to the first excitation state.

Sea-Hoon Kim

Papers

Structure and Nonlinear Optical Properties of Lanthanide Borate Glasses