Investigation of photochromic films containing Na8Al6Si6O24(Br,S)2.

Hackmanite (Na8(Al6Si6O24)(Cl,S)2), a sulfur-doped sodalite mineral, exhibits reversible photochromism, meaning it changes color under UV irradiation and fades back to its initial color when exposed to visible light or heat. This unique property makes hackmanite a promising candidate for applications in photochromic eyewear, optical coatings, and UV sensors. However, to be used in these applications, as-synthesized hackmanite powders need to be converted into versatile matrices, e.g. dispersed into polymeric films. In this context, the primary goal of this work was to determine the optimal synthesis conditions for hackmanite, enhance its photochromic response, and evaluate its suitability for photochromic films. Bromide was substituted for chloride in the hackmanite structure, and various synthesis parameters, including annealing and reduction temperatures as well as grinding duration were optimized to enhance the material's photochromic properties. In addition, aggregation control methods were explored separately during the preparation of silicone-based tenebrescent films to improve the uniformity of these composites. Hackmanite materials with optimized composition and photochromic response were selected for film fabrication. The results showed that achieving a higher color intensity was limited by increasing opacity. However, while hackmanite may not be ideal for transparent applications like eyewear, it could be used in UV sensors and similar applications where transparency is not a critical requirement. One such application, metameric anti-forgery tagging, was investigated and found to be a highly potential approach.