Optical Basicity

The concept of optical basicity (Λ) is particularly suited to binary oxides and oxidic network materials such as silicates to characterize the acid–base nature of glasses and melts and to account for the complexation of metal cations by a variety of anionic frameworks. It originates from chemical bonding studies on the interaction between donor oxygen atoms and probe ions, such as Pb2+ and Tl+, and enables the establishment of the optical basicity scale, from shifts in the ultraviolet (UV) frequencies of these probes. Correlation of Λ with chemical and physical properties allows trends to be related to chemical constitution. As a consequence, optical basicity finds application in such areas as glass science and technology and the refining properties of metallurgical slags. The development of noninvasive methods for obtaining Λ, coupled with probe-ion data, allows for a chemical bonding description of glass and of sites that are available for metal ions, whether field driven or static. It also apparently explains abnormal variations with composition, for example, in borate glasses, and emphasizes the importance of π-bonding in oxide systems. Optical basicity extends to other media, for example, fluoride–oxide glasses, chloride melts, and sulfides.