Color Controllable Inorganic Pigments with Ce3+ as a Color Source

Kazuki Yamaguchi; Yusuke Shobu; Ryohei Oka; Toshiyuki Masui

doi:10.1021/acs.inorgchem.3c01292

Color Controllable Inorganic Pigments with Ce³⁺ as a Color Source

Inorg Chem. 2023 Sep 25;62(38):15392-15402. doi: 10.1021/acs.inorgchem.3c01292. Epub 2023 Sep 13.

Authors

Kazuki Yamaguchi¹, Yusuke Shobu², Ryohei Oka³, Toshiyuki Masui¹

Affiliations

¹ Department of Chemistry and Biotechnology, Faculty of Engineering, and Center for Research on Green Sustainable Chemistry, Tottori University, 4-101, Koyama-cho Minami, Tottori 680-8552, Japan.
² Department of Engineering, Graduate School of Sustainability Science, Tottori University, 4-101, Koyama-cho Minami, Tottori 680-8552, Japan.
³ Field of Advanced Ceramics, Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Gokiso, Showa 466-8555, Nagoya, Japan.

PMID: 37702656
DOI: 10.1021/acs.inorgchem.3c01292

Abstract

The Ba₂RE_1-xCe_xTaO₆ (RE = La, Gd, Y; 0 ≤ x ≤ 1) pigments were synthesized by a conventional solid-state reaction method to develop environmentally friendly reddish inorganic pigments. The host was the double-perovskite-type Ba₂RETaO₆ (RE: rare-earth elements), and the color source was Ce³⁺. All Ba₂RE_1-xCe_xTaO₆ samples were obtained in a single-phase form as solid solutions. Rietveld refinement analysis of the Ba₂RETaO₆ (RE = La, Ce, Gd, and Y) samples revealed that the average bond length between RE³⁺ and O depends on the ionic radius of RE³⁺, and the shorter the RE-O length, the stronger the crystal field surrounding Ce³⁺. A photon energy at the maximum 4f-5d absorption of Ce³⁺ depended on the weighted average ionic radius (r_RE) at the RE³⁺ site (i.e., the crystal field energy around the Ce³⁺ ions). In response to this phenomenon, the sample color was changed in order to orange, red, pink, and violet with a decrease in the r_RE value, and a hue angle (h°) was roughly linearly related to that. For validation of the tendency, we demonstrated the synthesis and characterization of Ba₂La_0.5-yY_yCe_0.5TaO₆ to obtain a more reddish color. As we exactly expected, a more reddish color was obtained while maintaining a high C value. Furthermore, the h° values for y = 0.1 and 0.2 were in good agreement with our estimation. In light of the above results, by controlling the intensity of the crystal field surrounding Ce³⁺ and/or the concentration of Ce³⁺, the optical absorption wavelength and absorption intensity of the Ba₂RE_1-xCe_xTaO₆ system can be changed to adjust the color.