Cr and Mg co-doped YAlO3 red cool pigments with high NIR reflectance and infrared emissivity for sustainable energy-saving applications

Inorganic cool pigments with colors having high near-infrared (NIR) reflectance and infrared emission exhibit excellent application potential in reducing the energy consumption of buildings. In this work, a series of Cr and Mg co-doped YAlO3 red pigments were obtained by the co-precipitation method. The color properties and solar reflectance of the red pigments were regulated by tuning the amounts of Cr and Mg. The incorporation of Mg2+ can promote the generation of high-valent Cr ions and restrain absorption tail caused by oxygen vacancy. The pigment 3Cr–2Mg showed a good redness with L* = 54.55, a* = 34.05, and b* = 26.16, along with a high NIR reflectance of 71.5%. The NIR reflectance was further enhanced to 89.9% by tuning the contents of Cr and Mg. In outdoor experiments, the 1Cr-0.5 Mg coating maintained a temperature that was 10.5 °C and 7.9 °C lower than the blank cement coating and the commercial Fe2O3 coating temperatures, respectively, at noon solar radiation of up to 998 Wm-2. All pigments had high infrared emissivity (8–14 μm). A temperature of 2.1 °C lower than the ambient temperature could be obtained with the coatings at night.