Highly Tenebrescent Hackmanites from Natural Nepheline

Abstract

Photochromic hackmanites (Na,K)8Al6Si6O24(Cl,S)2, were synthesized with a solid state reaction route using natural nepheline, (Na,K)AlSiO4, as a starting material together with NaCl, KCl and Na2SO4. Hackmanite was obtained using NaCl, whereas with KCl the nepheline reacted only partially. Especially materials synthesized with NaCl showed a deep photochromic color under UV irradiation as well as good sensitivity to even low solar UV index values. This suggests that the material is well suited for personal solar UV exposure monitoring.