Control of Optical Reflection in Ca2MgWO6 by Co and Mo Doping

Abstract

To develop novel inorganic red pigments without harmful elements, we focused on the band structure of Ca2(Mg, Co)WO6 and attempted to narrow its bandgap by replacing the W6+ sites in the host structure of Mo6+. Ca2Mg1−xCoxW1−yMoyO6 (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 Ca2Mg1−xCoxW1−yMoyO6 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 Mo6+ content. This is because a new conduction band composed of a Co3d-W5d-Mo4d hybrid orbital was formed by Mo6+ 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 Ca2Mg1−xCoxW1−yMoyO6 system can be controlled to change the color by adjusting the bandgap energy.