Novel near-infrared reflective black inorganic pigment based on cerium vanadate.

Gd-doped cerium vanadates, Ce Gd VO (0 ≤ ≤ 0.30), were synthesized as near-infrared (NIR) reflective black pigments by a conventional solid-state reaction method. Crystal structure, particle size, optical properties, and color of the samples were characterized. The Ce Gd VO (0 ≤ ≤ 0.30) samples were obtained in a single-phase form and the lattice volume decreased with increasing Gd concentration. Optical absorption below 630 nm was observed in all samples, which corresponded to the charge-transfer transition between Ce and V orbitals. The absorption spectrum of Ce Gd VO was shifted to the longer wavelength side as the Gd content increased, because of the increase in the crystal field around V due to the lattice shrinkage. As a result, the sample color gradually changed from dark brown to black with increasing Gd content. Among the samples synthesized in this study, CeGdVO absorbed visible light with wavelengths shorter than 650 nm and exhibited the darkest color. Furthermore, this black pigment showed a sufficient NIR reflectance value ( = 66.3%), which was higher than those of the commercially available products ( < 50%).