A promising inorganic YFeO3 pigments with high near-infrared reflectance and infrared emission

The colored non-toxic near-infrared (NIR) reflective and infrared radiative pigments are desired in reducing the energy consumption of buildings. In this work, yttrium ferrite (YFeO3) pigments with controllable crystalline structure were successfully synthesized via the method of solid-state reaction at low-heating temperature. The effects of the crystalline structure and microstructure, especially charge state distribution, on the bandgap, chromatic properties, infrared reflection and radiation performance of YFeO3 pigments were investigated for the first time. With the calcining temperature increased, the structure of obtained pigments changed from hexagonal to orthorhombic, and the bandgap was obviously widened. The black hexagonal YFeO3 pigments possessed small particle size, and their intensive optical absorption in the NIR range was related to the noticeable multiple reflections induced by the grain boundary. While, the brown orthorhombic YFeO3 powdered pigments, as well as the corresponding pigmented coatings, possessed good NIR reflection characteristics, and the high solar reflectance values clearly highlight the potential of these pigments as cool pigments. In addition, the obtained YFeO3 pigmented coatings showed high emissivity in 8-14 mu m waveband (atmospheric window), indicating their potential applications in energy saving of buildings by combining NIR shielding and space cooling. The larger amount of Fe2+-Fe3+ ions pairs in the orthorhombic pigments led to the enhancement of free carrier absorption, which enhanced infrared emission and contributed to the slightly decreased NIR reflectance.