Synthesis and characterization of environmentally benign inorganic pigments with high NIR reflectance: Lanthanum-doped BiFeO3

- The near-infrared reflectance of Bi1-xLaxFeO3 (x = 0, 0.1, 0.2, 0.3, 0.4) particles was studied for the first time.
- Doping of La3+ for Bi3+ in BiFeO3 changed the color hue from black brown to reddish brown.
- The pigments exhibited higher NIR solar reflectance both in powdered form and in coating form than conventional pigment.
- The pigments possessed good thermal and chemical stability.
- The pigments demonstrated their potential serve as cool pigments.

A new environmentally benign near-infrared reflectance pigment based on BiFeO3 doped with La3+ was described. The pigments of the formula Bi1-xLaxFeO3 (x = 0, 0.1, 0.2, 0.3, 0.4) were characterized by XRD, FE-SEM, TG-DTA, UV-vis-NIR spectrophotometer and CIE L∗a∗b∗ color scales. The results reveal that the pigments crystallized at 600 °C with particle size less than 70 nm. The substitution of La3+ for Bi3+ in BiFeO3 shift the color from dark brown to reddish brown and the band gap decrease from 2.24 to 2.03 eV due to O2p-Fe3d charge transfer transitions. The near-infrared solar reflectance of the powdered pigments increased with the increase of progressive doping of La3+ for Bi3+. The pigment coated on concrete cement substrate exhibit higher near-infrared solar reflectance (R∗ ≥ 44.1%) than conventional coating of similar color. Moreover, the thermal and chemical stability of the pigments were also evaluated. In conclusion, the pigments have the potential to be applied as “cool pigments”.