Synthesis of near-infrared absorbing materials based on copper phosphate compounds

This work presents the synthesis of near-infrared absorbing materials based on copper phosphate by wet chemical precipitation with calcined temperatures of 250–750°C. At lower temperatures, it resulted in libethenite. From 450°C, copper oxy bisphosphate was formed and then transformed to copper dioxide bis(phosphate) and copper orthophosphate at 550–650°C. Sequently, copper dioxide bis(phosphate) decomposition was at 750°C. These thermal products showed significant changes in crystalline phase, morphology, and vibration characteristics, as well as the optical properties of obtained samples. While the samples treated at 250, 350, and 450°C gave pale colours, the ones calcined at 550, 650, and 750°C exhibited darker colours but stronger near-infrared absorbing ability.