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High near-infrared (NIR) reflective pigments have broad application prospects in alleviating urban heat island effect. But in fact, an easy and efficient method of preparing non-toxic and high near-infrared reflective pigments remains a desired choice for energy-saving coatings. In this research, several Mn doped YBO 3 pigments, possessing gray-blue and high near-infrared reflectance, were effectively prepared by solution combustion method. Relevant techniques were used to characterize the crystalline structure, morphology feature, optical properties, chemical tolerance, and heat insulation effect of the prepared pigments. The results presented that the color of powders varied from white to gray-blue due to the Mn doping. The band gap energy increased from 2.03 eV to 2.14 eV as the doping amount raised, and it could be assigned to the charge transfer transition between O 2p valence bands and Mn 3d conduction bands. The typical YB 0.97 Mn 0.03 O 3 pigment stated the excellent near-infrared reflectance of 66.18% and significant color properties (L* = 69.75, a* = −5.46, and b* = −6.36). Notably, the surface temperature of YB 0.97 Mn 0.03 O 3 coating is 39.5 °C lower than the gray-blue commercial pigmented coating. This work demonstrated that the prepared pigments with rather high reflectance possessed potential application in energy-saving materials for buildings. [ABSTRACT FROM AUTHOR]

Superfine CaLaAl 1-x Cr x O 4 (x = 0.02, 0.05, 0.08, 0.10) red ceramic pigments have been prepared by solution combustion reaction and subsequent high-temperature calcination. All of the pigments were characterized by X-ray diffraction (XRD), Field scanning electron microscopy (FESEM), UV–Vis spectrophotometry, Laser particle size analyzer and CIE L*a*b* spectrophotometry. Moreover, the effects of the doping amount of Cr3+ ion, calcination temperature, salt assistance and synthetic routes on chromatic performance and particle size distributions of the pigments were also investigated. The results showed that CaLaAl 1-x Cr x O 4 pigment particles prepared via solution combustion reaction and subsequent calcination were well-dispersed and uniform in size. With the increase of doping amount of Cr3+ ion, the brightness value L* of CaLaAl 1-x Cr x O 4 pigments decreased obviously and the redness value a* increased gradually. When x = 0.08, it showed the best chromatic performance (L* = 39.37, a* = 21.33, b* = 13.99). In addition, the synthetic pigments possess excellent high temperature stability which is conducive to the application of ceramic pigments. Most importantly, the synthetic method of CaLaAl 1-x Cr x O 4 red ceramic pigments is not only cheap in raw materials, but also easy to industrialize. [ABSTRACT FROM AUTHOR]

• Novel yellow-green Al-doped Y 3 Fe 5 O 12 nano-pigments are effectively synthesized via solution combustion method. • The Y 3 Fe 4 AlO 12 nano-pigments demonstrate the high NIR reflectance of 87.66% and great acid/alkali resistance. • Compared with the similar commercial pigment, 7.6 °C can be reduced by Y 3 Fe 4 AlO 12 pigment. • The synthetic pigments have potential to be used in cool coatings and to mitigate the urban heat island effect. The pigments with high near-infrared (NIR) reflectance hold great promise toward both fundamental types of researches and applications for the realization of comfortable indoor-temperature by mitigating urban heat island effect. However, the facile yet simple method for the NIR reflective pigments with bright color and non-toxic feature remains a huge challenge, limiting their practical application. Herein, we proposed a mild and universal method of solution combustion for constructing the non-toxic and NIR reflective yellow-green pigments of Al-doped Y 3 Fe 5 O 12. The Y 3 Fe 4 AlO 12 pigment presented a high NIR reflectance of 87.66%, and an outstanding acid/alkali resistance. Moreover, the pigment had an impressive color performance (L* = 78.72, a* = − 4.05, b* = 40.04). Besides, the practical near-infrared reflection performance revealed that the transient surface temperature of the Y 3 Fe 4 AlO 12 pigment was 7.6 °C lower than that of the pigment with similar color on the market. This research supplied high NIR reflecting pigments of Y 3 Fe 5−x Al x O 12 as promising coatings for roofs and exterior walls of buildings, acting as a favorable solution for urban heat island effect. [ABSTRACT FROM AUTHOR]