Fig. 3. Reversible photochromic mechanism.
a, c XPS spectra of W element in WPG-Sb1 before (a) and after (c) photochromism (PC) (151.26 W cm−2, 15 min). b, d XPS spectra of Sb element in WPG-Sb1 before (b) and after (d) photochromism (151.26 W cm−2, 15 min). e, f XPS spectra of W (e) and Sb (f) elements in the decolorated (DC) glass caused by heat-treatment at 300 °C for 10 min. g Proposed reversible photochromism mechanism of tungsten phosphate glass.