Many metal ions impair ultraviolet transparency when present in glass
owing to charge transfer absorption bands. Existing relevant spectrosc
opic data, although limited, do indicate that the principle of optical
electronegativity can be applied and that the onset of ultraviolet im
pairment is linked to the state of polarisation of the oxygen atoms. L
inking optical electronegativity with optical basicity allows a rough
estimation of frequency shift for changes in glass composition.