Environmentally Friendly Inorganic Red Pigments Based on Bismuth Oxide

Abstract

Novel inorganic red pigments based on bismuth oxide, [(Bi1−xErx)1−yFey]2O3 (0 < x ≤ 0.50, 0 < y ≤ 0.30), were synthesized by a conventional solid-state reaction method, and their color properties were characterized. The color of the sample depended on its composition, with the [(Bi0.72Er0.28)0.80Fe0.20]2O3 pigment having the most vivid red hue. The a* value corresponding to red chromaticity of the [(Bi0.72Er0.28)0.80Fe0.20]2O3 pigment was +30.9, which was greater than that of a commercial Fe2O3 pigment (a* = +28.9). Since these pigments are composed of nontoxic and safe elements, they can be effective alternatives to the conventional Fe2O3 pigment.

Photonic glass for high contrast structural color

“…It can be derived as the effective power scattered per single particle divided by the incident light intensity using equations (1) and (5). Figure 5 shows the scattering cross section per particle normalized by the particle geometrical cross section which represents the particle scattering efficiency compared for two PhGs: the homogenous solid silica particle PhG (with the FT shown by Figure 2b) is shown by Figure 5a and the core-shell particle PhG (with the FT shown by Figure 4c) is shown by Figure 5b, respectively.…”

“…The commercial pigment based color derives from light absorption by electron transitions and is dependent on the presence of a defined chemical structure, which can be altered by UV radiation during later use or high temperature processing during manufacturing [2,4]. Also, some of the pigments contain toxic materials that can be harmful in production or disposal, initiating the need for alternatives [2,5,6]. At the same time, structural colors depend on the refractive index distribution, only and thus can be produced from environmentally friendly materials such as silica, alumina, zirconia etc.…”

Novel environment-friendly inorganic red pigments based on (Bi, Er, Y, Fe)2O3solid solutions

“…However, the band gap energy of the ((Bi 0.72 Er 0.28 ) 0.80 Fe 0.20 ) 2 O 3 pigment became too low because of significant lattice shrinkage, and the optical absorption extended into the red region. As a result, the red color was not so vivid, although it was higher than that of the commercial Fe 2 O 3 pigment (a* = +28.9) [13]. In this study, therefore, a part of the Er 3+ (0.103 nm) [14] site was substituted with larger Y 3+ ions (0.104 nm) [14] to relax the excessive lattice shrinkage.…”

“…The ((Bi 0.72 Er 0.28−x Y x ) 1−y Fe y ) 2 O 3 (0 < x ≤ 0.28, y = 0.20) pigments were synthesized using a conventional solid-state reaction method. As is the case with the ((Bi 0.72 Er 0.28 ) 0.80 Fe 0.20 ) 2 O 3 pigment [13], double calcination was adopted in the synthesis process to obtain the ((Bi 0.72 Er 0.28−x Y x ) 1−y Fe y ) 2 O 3 solid solutions certainly. In the first process, (Bi 0.72 Er 0.28−x Y x ) 2 O 3 solid solutions were prepared in a single-phase form of the cubic ␦-Bi 2 O 3 structure, and in the second one, Fe 3+ ions were introduced into the (Bi 0.72 Er 0.28−x Y x ) 2 O 3 lattice maintaining the single-phase ␦-Bi 2 O 3 structure.…”

“…In our previous study, we elucidate that the high-temperature ␦-Bi 2 O 3 phase was stabilized at room temperature by introducing Er 3+ ions into the Bi 3+ site, and that the red chromaticity was significantly increased by further dissolution of Fe 3+ into the lattice to insert the Fe3d level as a new energy level below the Bi6P conduction band. In particular, it was found that a ((Bi 0.72 Er 0.28 ) 0.80 Fe 0.20 ) 2 O 3 pigment showed the highest redness value (a* = +30.9 in the CIE L*a*b* system) [13]. However, the band gap energy of the ((Bi 0.72 Er 0.28 ) 0.80 Fe 0.20 ) 2 O 3 pigment became too low because of significant lattice shrinkage, and the optical absorption extended into the red region.…”