Overview of the environment of Ni in oxide glasses in relation to the glass colouration.

Using two complementary methods: x-ray absorption and crystal field spectroscopies, the Ni sites and their distribution in glass have been determined, in order to rationalise the structural dependence of glass properties. In borate glasses, the structure of the glass related to its composition is responsible for the Ni environment and the glass colour. In borosilicate glasses, depending on its nature and alkali content, colours may show high variability as the Ni environment responds to the mixing of two interconnected (B and Si) sublattices. In silicate glasses, the short range order around Ni is mostly characterised by low and unusual coordination numbers (Ni-[4] and Ni-[5]), imparting to the glass specific brown and purple colourations. The proportion of such sites also depends on the composition