Buildup of afterglow in photochromic sodalite
Photochromic sodalite, Koksha valley, Badakhsha, Afghanistan, 310 nm LED. The white fluorescence is due to Ti3+. At the same time there is a slow buildup of afterglow (PeL) from the same Ti-defect. Initially you still see a remainder of the orange fluorescence from the S2- defect, but slowly it gets dominated by the white. At the same time the purple colouring increase due to a Cl-vacancy that traps an electron from the S2- . The spectrum shows the build-up in the blue at increasing time. The presence of Fe3+ destroys the white fluorescence and afterglow.