Photochromic materials are deeply investigated experimentally and theoretically because of their numerous possible high-tech applications going from adaptive glasses to optical memory. Geologists have known for almost one century the existence of natural photochromic minerals of the sodalite family. Although the community is trying to develop new type of photochromic materials, almost no efforts were devoted to understand and develop these photochromic minerals known in geology for a long time.
In this presentation, we will start from the natural sulphur-doped sodalite mineral formula to understand its spectroscopic properties. By combining periodic boundary conditions and embedded cluster-type approaches, we bring a theoretical overview of the photochromism mechanism. Our TD-DFT calculations of sodalite systems containing electrons trapped into chlorine vacancies (called F-center) showed absorption spectrum and a simulated color in agreement with experiment. TD-DFT and post-Hartree-Fock calculations were also operated on S22- containing systems in order to determine the exact mechanism of coloration and discoloration, supporting that the key step is a direct through space charge-transfer between S22- ion and a chlorine vacancy. The bleaching activation energy of 0.3 eV obtained from the quantum chemical calculations is now confirmed experimentally based on a new experimental protocol designed to measure this activation energy .
Based on these results, we successfully proposed a way to tune the wavelength of coloration of the artificial sodalites proving that these materials can be easily synthetized and designed for specific applications.
 Inorg. Chem. 56, 414 (2017).
 Mater. Horizons 5, 569 (2018).