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Enhanced near infrared (NIR) solar reflectance with interesting yellow hues in a new series of scheelite type solid solutions, [(LiLaZn) x/3Bi1–x ]­[Mo x V1–x ]­O4 (x = 0, 0.1, 0.2, 0.3, 0.4) were synthesized via conventional solid state reaction (SSR) method and planetary ball milling assisted solid state reaction (PBM) method. The structural, morphology, and reflectance (absorption) properties and coloring performance of the prepared compositions were analyzed by various advanced techniques. The solid solutions undergo a phase transformation from a monoclinic to a tetragonal phase. The compounds exhibit strong absorption in the UV and blue regions of the visible spectrum displaying high NIR reflecting intense yellow shades ranging from reddish to greenish. The yellow hue and NIR reflectance is enhanced by the morphological modifications through PBM method. Typically, the pigment [(LiLaZn)0.099Bi0.7]­[Mo0.3V0.7]­O4 displayed intense yellow color (b* = 86.63) with NIR reflectance of 95% much better values than the commercial sicopal yellow. The applicability studies of these pigments on concrete cement block and metal sheet imparts good coloring performance with high NIR solar reflectance. Chemical and light resistance tests indicate their durability in the extreme weathering conditions. Thus, the prepared compositions consisting of less toxic elements demonstrate sustainable use of the present pigments in exterior surface coating applications as energy saving products.

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Brilliant IR reflecting yellow colorants are developed in rare earth double molybdate substituted BiVO 4 solid solutions. Li 0.10 RE 0.10 Bi 0.8 Mo 0.2 V 0.8 O 4 (RE = La, Pr, Sm, Gd, Tb, Dy, Y, Yb and Lu) pigments are prepared by a conventional solid-state reaction route and their optical, structural and morphological properties are analyzed. X-ray diffraction analysis confirms the tetragonal scheelite phase formation in the series. These pigments have a strong optical absorption in the UV-blue light wavelength region. CIE LAB color analysis shows that different hues of yellow shades are obtained in these solid solutions. The color characteristics are comparable to commercial BiVO 4 pigment. Incorporation of double rare earth molybdates of La, Gd, Tb, Y and Lu into BiVO 4 results in nontoxic IR reflecting cool pigments. The applicability of the developed pigment was tested on a concrete cement surface as well as on a metal panel. These pigments are composed of less toxic elements that make them favorable for energy saving surface coating formulations for buildings and automotives.The urban heat island effect emerging in metropolitan cities produces elevated urban air temperatures. Solar radiation consists of about 5% ultraviolet radiation, 46% visible radiation and 49% infrared radiation. A major contribution of heat comes from the IR radiation, which transfers heat to the underlying structure in buildings and automotives causing thermal discomfort and health problems. A substantial amount of energy is consumed to cool buildings, thus increasing energy demand. 1 Cool paints absorb less solar energy, which keeps the surface at a lower temperature and decreases energy transfer by radiation. Passive cooling of buildings helps reduction in air pollution due to low energy usage and power plant emissions. Therefore, current interest in the pigment industry is focused on developing nontoxic cool pigments that aid in energy savings. 2 Bright yellow shades are particularly challenging, with preferential reformulation away from cadmium pigments and lead chromates within the plastics and surface coating markets. 3 There is an urgent need for developing IR reflecting nontoxic yellows, which are limited in the current market.Recently, BiVO 4 has attracted wide attention for its photocatalytic, 4 ferroelastic, 5 dielectric, 6 ionic and electronic conductive properties, 7 which makes it attractive for use in gas sensors, 8 microwave resonator devices, 6 wastewater treatment 9 and water splitting. 9 BiVO 4 has been identified as an ideal candidate for pigmentary applications. 10 Recently, many researchers, including our group, have reported BiVO 4 based pigments such as (Bi, La)VO 4, 11 (Bi, Ca, Zn)VO 4, 12 (Bi, Ca, Zn, La)VO 4, , 13 Y and Nb doped BiVO 4 14 and SiO 2 coated BiVO 4. 15 So, development of nontoxic IR reflecting BiVO 4 based pigments can lead to cool surface coating formulations for buildings and automobile shells.Double alkali rare earth molybdates and tungstates of the type ARE(XO 4 ) 2 ; X = Mo, W 16 have a va...

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A new series of red phosphors based on Eu(3+)-doped yttrium cerate [Y1.9Ce2O7:0.1Eu(3+), Y2Ce1.9O7:0.1Eu(3+) and Y2Ce2-xO7:xEu(3+) (x = 0.05, 0.10, 0.15, 0.20, 0.25 and 0.50)] was prepared via a conventional solid-state method. The influence of the substitution of Eu(3+) at the aliovalent site on the photoluminescent properties was determined by powder X-ray diffraction, FT Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy with energy-dispersive spectroscopy, UV-visible absorption spectroscopy, photoluminescence spectroscopy and lifetime measurements. The substitution of Eu(3+) at the Ce(4+) site induces a structural transition from a defect fluorite to a C-type structure, which increases the oxygen vacancy ordering and the distortion of the Eu(3+) environment, and decreases the formation of Ce(3+) states. In contrast, phosphors with isovalent substitution at the Y(3+) site exhibit the biphasic nature of defect fluorite and a C-type structure, thereby increasing the number of Ce(3+) oxidation states. These modifications resulted in remarkable changes in the photoluminescent properties of Y2Ce1.9O7:0.1Eu(3+) red phosphors, with emission intensities 3.8 times greater than those of the Ce0.9O2:0.1Eu(3+) and Y1.9Ce2O7:0.1Eu(3+). The photoluminescent properties of Y2Ce2-xO7:xEu(3+) were studied at different Eu(3+) concentrations under excitation with blue light. These phosphors emit intense red light due to the (5)D0-(7)F2 transition under excitation at 466 nm and no concentration quenching is observed with up to 50 mol% Eu(3+). They show increased lifetimes in the range 0.62-0.72 ms at Eu(3+) concentrations. The cation ordering linked to the oxygen vacancy ordering led to the uniform distribution of Eu(3+) ions in the lattice, thus allowing higher doping concentrations without quenching and consequently increasing the lifetime of the (5)D0 states. Our results demonstrate that significant improvements in the photoluminescence properties can be achieved by the structural alteration of a fluorite CeO2 to a C-type lattice.