New shades of photochromism - yellow sodalites for the detection of blue light

The absorption energy of the F-center in photochromic sodalite can be lowered by expanding the unit cell with larger ions, changing the color from pink to blue. Blue-shifting this absorption to produce other colors is not so straightforward. In this work, sodalites of the formula Na 2−2 x Ca x (Na,K) 6 (AlSiO 4 ) 6 (Cl,S) 2 displaying white-to-yellow photochromism have been prepared and thoroughly characterized. Combining spectroscopic experiments and quantum chemical calculations, the formation of a Na 2 Ca entity inside the sodalite cage surrounding the trapped electron responsible for the yellow color is postulated. Optimal yellow photochromism occurs for 0.13 ≤ x ≤ 0.18, while at x ≥ 0.27 the formation of the by-product davyne begins to affect the structure and optical properties. Finally, the sensitivity of these materials to blue light is shown to make them well-suited as sensors for blue light over-exposure e.g. from computer screens or smart phones. Sodalites showing white-to-yellow photochromism have been developed by partial substitution of sodium with calcium. The yellow colour is sensitive to fading under blue light, making these low-cost materials highly suitable for blue light detection.