Photochromic sodalite, Na8(AlSiO4)6(Cl,S)2, has been a topic of research for almost 100 years, though only recently has a deep understanding of its remarkably fatigueresistant colour change been obtained. Aside from the cathodochromic displays proposed in the 1970s, photochromic sodalites have only been seriously considered for everyday and industrial applications in the last decade, and for some of these significant development was needed before potential commercialisation.

Following on from prior investigations into the colour and excitation threshold of photochromism, this thesis studies how the colour change of photochromic sodalite can be tuned to switch from white to any desired colour, presenting a range of possible absorption maxima from 420-680 nm: almost the entire visible spectrum. Particularly interesting was the effect of sodium substitution with calcium, which produced sodalites showing a remarkable white-to-yellow colour change. The relative efficiency of four different synthesis methods was considered for producing the best photochromic sodalites, including a thorough characterisation of the bluewhite luminescence of photochromic sodalite produced without zeolite A. Postsynthesis treatment such as sintering of hydrothermal samples and nitrate-melt ion exchange is also discussed in the context of redshifting the F-centre’s absorption maximum as much as possible. The suitability of a diverse range of photochromism colours from a single or mix of low-cost sodalite materials for several industrial applications, including X-ray imaging and blue light detection, is discussed.

The effect of selenium on the photochromism was also studied: selenium was gradually introduced into the sodalite structure to replace the usual sulfur activator. Selenium was found to lower the activation threshold of photochromism without affecting the energy levels of the F-centre’s absorption, unlike potassium and rubidium. Selenium sodalites were then mixed with selenium-free materials of a complementary colour, and with the aid of a mathematical model, such mixtures were shown to be suitable for simultaneous passive dosimetry of two types of UV radiation.

The deeper scientific understanding of the photochromism mechanisms and the tuning methods presented in this work thus serve to improve these materials’ suitability for further research and commercialisation.