Novel Bi3+ doped and Bi3+/Tb3+ co-doped LaYO3 pigments with high near-infrared reflectances

Abstract

A series of environmentally benign and high NIR reflective pigments based on Bi3+ doped and Bi3+/Tb3+ co-doped LaYO3 are synthesized via the sol-gel method. The resulting powders were characterized by X-ray diffraction, UV–vis–NIR spectrophotometer and CIE L*a*b* (1976) color space. The doping of Bi3+ for La3+ in LaYO3 results in the color changes from light yellow to dark yellow and Bi3+/Tb3+ for La3+ in LaYO3 varies from soft orange to dark orange. Meanwhile, the band gaps of pigments decrease from 4.52 eV to 2.95 (Bi-doped) and 2.15 eV (Bi/Tb co-doped). Interestingly, the Bi-doped pigments possess high NIR solar reflectance (>95%) in the range of 700–2500 nm. In contrast, the Bi/Tb co-doped pigments decrease the NIR solar reflectance from 98.28% to 78.77%. The applicability studies of La0.5Bi0.5YO3 and La0.5Bi0.25Tb0.25YO3 pigments with TiO2 base coat on galvanized sheet reveal good coloring performance with high NIR reflectance. Acid/alkaline tests indicates good chemical stabilities of the pigments under the extreme weather conditions. The superior performances of developed pigments have revealed potentials to be employed in cool coatings.