Environment-friendly pigments based on praseodymium and terbium doped La2Ce2O7 with high near-infrared reflectance: Synthesis and characterization

The environmentally friendly pigments based on Pr4+ and Tb4+ doped La2Ce2O7 have been synthesized via the Sol-Gel method and characterized using several analytic techniques, such as XRD, UV-vis-NIR spectrophotometer and CIE L*a*b* (1976) color space. The investigation has demonstrated that the doping of Pr4+ or Tb4+ for Ce4+ in La2Ce2O7 resulted in the color changes from light yellow, soft orange to dark orange. Moreover, the band gaps of pigments decreased from 3.34 to 2.37 (Pr-doped) and 2.24 (Tb-doped). The synthesized pigments of La2Ce2-xPrxO7 and La2Ce2-xTbxO7 (x = 0, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5) were disordered defect fluorite-type structure and showed good chemical stabilities in acid/alkaline tests. Interestingly, the Pr4+ doped pigment possessed high NIR solar reflectance (>72.47%) in the range 700-2500 nm with the color of dark orange (L* = 46.87 a* = 13.5 b* = 13.4). The substitution of Tb4+ for Ce4+ changed the color to dark orange (L* = 51.35 a* = 15.94 b* = 17.57), and decreased the NIR solar reflectance slightly from 99.11% to 87.41%. The applied studies of two kinds of pigments coating on the galvanized sheets exhibited nice colors with high NIR solar reflectance. The superior performances of pigments have rendered them competent as qualified exterior coating materials.