High-performance NIR reflective yellow pigment for sustainable cool surface coatings to address urban heat island mitigation

Abstract

A novel, environmentally friendly, near-infrared (NIR) solar reflective yellow pigment has been successfully developed by incorporating bismuth (Bi3+) and vanadium (V5+) into the yttrium phosphate (YPO4) host lattice. Y(1􀀀 x)BixP(1􀀀 y)VyO4 (x = y = 0–1) materials with different composition were synthesized using two distinct approaches: the flux-assisted solid-state method (SSM) and the co-precipitation technique (CPS), and the results were compared. A drastic shift in the absorption curve towards higher wavelengths is observed for the materials synthesized by the solid-state reaction method and co-precipitation at 900 ◦C. Secondary phases were noticed in both methods of preparation due to the high ionic radii of the dopant ions. Notably, the simultaneous incorporation of Bi3+ and V5+ significantly enhanced both the NIR solar reflectance and the intensity of the yellow color in the synthesized materials. The co-doping effect induced a well-defined morphology, improving the lightscattering efficiency and boosting the NIR solar reflectance. The optimized composition, Y0.4Bi0.6P0.4V0.6O4, achieved a high reflectance value of 54.64%, compared to just 38% for the undoped host. With a vivid yellow body color, high solar reflectance (54.64 %), and excellent stability, Y0.4Bi0.6P0.4V0.6O4 emerges as a promising, sustainable alternative for cool yellow pigments in energy-efficient coatings and architectural applications.