Synthesis and characterization of Fe/Mn co-doped CuCr2O4 black pigment with high near-infrared reflectance

Abstract

A deep black near-infrared reflectance pigment based on CuCr2O4 doped with Fe and Mn ions was described. The formula of the pigment was CuCr2-x-yFexMnyO4. The band gap of pigments decreased from 1.25 eV to 1.00 eV along with the substitution of Fe3+ and Mn3+ for Cr3+ in CuCr2O4. This change originated from the charge transfer of O2p to Fe3d and Mn3d, and d-d intra-atomic transitions of Fe and Mn ions, which resulted in the decrement of L* from 21.21 to 17.72. For doped CuCr2O4, the higher NIR reflectance could be attributed to the decrease of free carries. For the depressions of reflective spectra at around λ = 1240 nm(1 eV) for doped CuCr2O4, the electronic transition between defect levels and conduction band could be the main reason. The optimal R* was 27.7%, which was higher than 19% of CuCr2O4. CuCr1.93Fe0.07O4 and CuCr2O4 were selected for building roof coating to determine the thermal insulation effect, and CuCr1.93Fe0.07O4 was better than CuCr2O4. Therefore, CuCr2-x-yFexMnyO4 pigments could be used as cool coatings for building roofs.