Potential NIR reflecting yellow pigments powder in monoclinic scheelite type solid solutions: BiVO4-GdPO4 for cool roof applications

A new series of reddish yellow pigments powder are developed in monoclinic scheelite (s-m) type structure of (BiV)1-x(GdP)xO4. The morphology of the pigment powder particles exhibits a decreasing trend in the particle size on GdPO4 substitution that allows uniform dispersion in the matrix. The UV–vis NIR spectra shows intense absorption in ultraviolet and blue regions with increased reflectance in the NIR wavelength region. The substitution shifts the absorption edge towards the blue side allowing to tune the band gap from 2.29 to 2.35 eV resulting in different shades of intense yellow hues with typical color coordinates of L* = 73.38, a* = 8.22, b* = 65.42 for x = 0.06. The color imparting of the pigment in a poly methyl methacrylate matrix shows intense yellow coloration without any loss of color strength. The above results demonstrate that the solid solutions of BiVO4 and GdPO4 make them eco-friendly yellow cool colorants for surface coating applications to reduce the heat buildup and mitigate the energy cost for the cooling.