The effect of various compositional substitutions on the colour of long-lived F-centres in the sodalite structure has been investigated by the synthesis and characterisation of several phases of the general composition A8[M′M″O4]6[X,S]2. The visible-region absorption spectrum of the excited state, formed by 256 nm irradiation of the as-synthesised materials, shows a broad absorption whose position correlates with the dimensions of the sodalite cage occupied by the excited electron.
Williams, E. R., Simmonds, A., Armstrong, J. A., & Weller, M. T. (2010). Compositional and structural control of tenebrescence. Journal of Materials Chemistry, 20(48), 10883-10887. https://doi.org/10.1039/c0jm02066d