Synthesis and Characterisation of Mg2+ and Al3+ Co-Doped CoCr2O4 Inorganic Pigments With High Near-Infrared Reflectance

A new class of near-infrared (NIR) reflectance pigments based on Co 1?x Mg x Cr 2?y Al y O 4 (x = 0–1 and 0–2) was synthesised using the Pechini-type sol-gel process. The developed powders were characterised by thermogravimetry differential scanning calorimetry, X-ray diffraction (XRD), ultraviolet–visible diffuse spectroscopy, colour Commission Internationale del'Eclairage (CIE) 1976 (L * a b ) scales. XRD patterns revealed characteristic peaks spinel structure with good crystallinity. Substituting 2+ for ions in tetrahedral positions 3+ octahedral CoCr 2 reduces cost changes pigment (green to yellow then blue). Moreover, exhibited high NIR solar 780–2,500 nm wavelength range. thermal chemical stability also studied. Our findings demonstrate potential applying these cool colourants.