Glass - Back to the Future!

Presenting Author:
Quyen Le

article posted 7 April 2016

Quyen Le in 2006 got her BSc, Chemical Engineering, CanTho University, Viet Nam. In 2009 a Master of Engineering Advanced Manufacturing Technology, University of South Australia, Australia. Then in 2015 started a PhD at Otto Schott Institute of Materials Research, Friedrich Schiller University of Jena, Germany.

Cu2+ as probe ions in covalent and ionic glass systems with varying optical basicity [Lambda]th from 0·3 to 0·8

Q.H. Lea, F. Linda, D. Mönckea, W. Plassb & L. Wondraczeka
a Otto-Schott-Institut of Materials Research, Friedrich- Schiller-Universität, Fraunhoferstraße 6, 07743 Jena, Germany
b Institut für Anorganische und Analytische Chemie, Friedrich- Schiller-Universität, Humboldtstr. 8, 07743 Jena, Germany

When comparing the site environment and bonding characteristics of dopants, such as d transition metal ions in glasses, the concept of optical basicity is an effective tool for the quantification of the ligand strength of otherwise totally different glass systems.
Duffy & Ingram quantified the parameter of basicity in terms of the optical basicity [Lambda], according to which an electron donor power of a glass matrix is assigned in relation to that of a pure CaO matrix for which the optical basicity was set at unity. The concept of optical basicity has been applied extensively to a wide range of oxide glasses but also to fluoride containing glasses. [Lambda]th, can be calculated from the glass composition using an increment system from basicity data of the oxide and fluoride components [1–5]. [Lambda], can be determined experimentally from the shift of an optical band maximum of a probe ion such as Pb2+ or Mn2+ [1–6].
The absorption spectra of Cu2+ are compared in a wide range of different glass systems ranging from covalent soda–lime–silica (NCS), borate and phosphate glasses, to ionic fluoride phosphate, to sulfophosphate glasses. Other glasses, such as telluride or antimonite glasses are also included in this study. The presence of the d9 ion Cu2+ results in a broad optical absorption band with a maximum at 740 to 850 nm, typical for Cu2+ ions in a Jahn–Teller distorted octahedral site. Electron spin resonance (ESR) measurements complement the UV-Vis studies for the characterization of the site geometry and bonding character of Cu2+. Therefore, g||, g|, A|| and A| values are determined from the hyperfine splitting of the Cu2+ resonance.
As polarizability of the ligands changes, or the electron donor power or basicity of the glass matrix, the ligand field surrounding Cu2+ will adjust and this is reflected in variations of the optical and magnetic parameter. This is shown in Figure 1 by the shift of the position of the Cu2+ absorption band with increasing optical basicity. Only the pure fluoride glass does not follow the trend, and other influents like a change in coordination might need to be considered for this glass.
For many glasses a linear shift of the absorption maximum can be observed as ligands are substitutes in a “nephelauxetic” like series such as BO4-, SiO42-, PO43-, SO42- (it should be noted that the number of non-bridging oxygen ions is critical in this series).

Figure 1: Correlation between position of the Cu2+ absorption band and optical basicity

For other glasses such as the fluoride phosphate glass series FPx, (100-x)(AlF3, (Mg/Ca/Sr)F2)-xSr(PO3)2 with x=0 to 40 and 70 to 100, preferential bonding of Cu2+ to phosphate ligands is observed in agreement with earlier findings for Pb2+ ions in FPx glasses [7]. Only for the phosphate-free fluoride glass the band maximum varies significantly compared from all phosphate containing glasses.

[1] J.A. Duffy, M.D. Ingram, Establishment of an optical scale for Lewis basicity in inorganic oxyacids, molten salts, and glasses, J. Am. Chem. Soc., 93 (1971) 6448-6454.
[2] J.A. Duffy, A common optical basicity scale for oxide and fluoride glasses, J. Non-Cryst. Solids, 109 (1989) 35-39.
[3] J.A. Duffy, Bonding, Energy Levels & Bands in Inorganic Solids, Longman Group UK Ltd, 1990.
[4] J.A. Duffy, A review of optical basicity and its applications to oxidic systems, Geochim. Cosmochim. Acta, 57 (1993) 3961-3970.
[5] J.A. Duffy, Optical Basicity: A Practical Acid-Base Theory for Oxides and Oxyanions, J. Chem. Educ., 73 (1996) 1138-1142.
[6] J.A. Duffy, M.D. Ingram, S. Fong, Effect of basicity on chemical bonding of metal ions in glass and its relevance to their stability, PCCP, 2 (2000) 1829-1833.
[7] L.L. Velli, C.P.E. Varsamis, E.I. Kamitsos, D. Möncke, and D. Ehrt, Optical basicity and refractivity in mixed oxyfluoride glasses, Phys. Chem. Glasses: Eur. J. Glass Sci. Technol. B 49 (2008) 182-187.