An intense purple chromophore based on Co2+ in distorted tetrahedral coordination

Abstract

An intense purple, cost-effective inorganic pigment LiZn1-xCoxPO4 (0.1 ≤ x ≤ 0.8) was synthesized by solid-state ceramic route and their structural, optical and chromatic properties were studied employing Powder X-ray Diffractometer and UV-Vis-NIR diffuse reflectance spectrophotometer techniques. Origin of an exotic intense purple colour of these pigments was investigated, by means of crystallographic as well as optical spectral studies. Structural refinement showed that chromophore of the pigment CoO4, formed with highly distorted geometry due to significantly shorter Co-O bonds. Structural changes attributed strongly on the spectral features leading to an excellent purple colour which is unusual for CoO4 tetrahedral coordination. The hue of the purple colour can be controlled by tuning the Co content. We accomplished an impressive NIR Solar reflectance (R* = 68%) and good chemical stability. The colour delivering performance of these purple pigments have also been evaluated by pigment incorporation in polymer matrix, where we were able to retain its excellent colour. Moreover, present work showed that these developed pigments can be a potential candidate for cool pigment by coating onto roofing materials like aluminum roofing sheets and concrete block.