COMMENTS ON THE APPLICATION OF OPTICAL BASICITY TO GLASS

The optical basicity of a glass can be calculated from parameters assigned to constituent oxides and the stoichiometry. Such calculations, when applied to a series of compositions in a glass system, indicate the trend in basicity and this is usually close to that obtained experimentally using probe ions such as Pb2+. Deviations between predicted and experimental optical basicity can be useful for detecting critical phenomena as, for example, in the Na2O-P2O5 glass system where Pb2+ indicates an optical basicity step at the 1:1 composition. The determination of optical basicity for UV opaque materials (where spectra of ions such as Pb2+ cannot be measured) using electronegativity relationships is critically assessed, and results are compared with those obtained from refractivity measurements. Assigned optical basicity values are given for 14 oxides including MnO and FeO (both of which have the value of 1.0).