Cathodochromism in Photochromic Materials

Photobleachable electron-beam-induced coloration has been observed in certain photochromic materials. This behavior is explained in the case of CaTi${\mathrm{O}}_3$: Fe-Mo by the trapping of electrons and holes at ${\mathrm{Mo}}^{6+}$ and ${\mathrm{Fe}}^{3+}$ ions, respectively, producing the colored state of the material. The material is restored to its uncolored state by the photo-induced transfer of an electron from ${\mathrm{Mo}}^{5+}$ to ${\mathrm{Fe}}^{4+}$.