Control of Optical Reflection in Ca 2 MgWO 6 by Co and Mo Doping.

To develop novel inorganic red pigments without harmful elements, we focused on the band structure of Ca 2 (Mg, Co)WO 6 and attempted to narrow its bandgap by replacing the W 6+ sites in the host structure of Mo 6+ . Ca 2 Mg 1- x Co x W 1- y Mo y O 6 (0.10 ≤ x ≤ 0.30; 0.45 ≤ y ≤ 0.60) samples were synthesized by a sol-gel method using citric acids, and the crystal structure, optical properties, and color of the samples were characterized. The Ca 2 Mg 1- x Co x W 1- y Mo y O 6 solid solution was successfully formed, which absorbed visible light at wavelengths below 600 nm. In addition, the absorption wavelength shifted to longer wavelengths with increasing Mo 6+ content. This is because a new conduction band composed of a Co 3d -W 5d -Mo 4d hybrid orbital was formed by Mo 6+ doping to reduce the bandgap energy. Thus, the color of the samples gradually changed from pale orange to dark red, with a hue angle ( h °) of less than 35°. Based on the above results, the optical absorption wavelength of the Ca 2 Mg 1- x Co x W 1- y Mo y O 6 system can be controlled to change the color by adjusting the bandgap energy.