Photochromism of vacancy-related defects in thermochemically reduced α‐Al2O3:Mg single crystals

Oxygen vacancies and their aggregates are produced much more readily in Mg-doped α‐Al2O3 than in undoped α‐Al2O3 single crystals during thermochemical reduction at high temperatures. A reversible photochromic effect was discovered in Mg-doped Al2O3 crystals containing large concentrations of oxygen divacancies. Alternate excitation with 5.0 and 3.69 eV light results in brown or yellowish–green coloration, respectively. The yellowish–green coloration can also be restored by thermal anneals at temperatures of about 750 K.