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New red phosphor materials of general formula Gd3-xMO7:xEu(3+) (M = Nb, Sb, and Ta) were prepared using a high temperature solid state reaction route. Detailed structural studies using XRD, FT-IR and Raman spectroscopic techniques showed that niobate and tantalate samples crystallized in the weberite type structure whereas the antimonate sample in the fluorite structure. Photoluminescence properties of the three compositions are correlated with their crystal structures. It was observed that more ordering occurs in the lattice when an M site is doped from Sb to Nb to Ta. Although niobate and tantalate samples possess similar structures more distortions were noticed in the tantalate sample increasing the radiative transition probabilities. Due to the more ordered structure of the Gd3TaO7 host lattice resulting in a more uniform distribution of Eu(3+) ions, the tantalate system showed better luminescence properties. The variation in the luminescence intensity with various Eu(3+) concentrations in the Gd3TaO7 host lattice was also studied to calculate the optimum doping concentration.

A new family of red phosphors, CeREO:0.1Eu (RE = Y and La; x = 0, 0.20, 0.40, 0.60, 0.80, and 0.90), was synthesized by a conventional solid-state route. The influence of contrasting rare earth substitutions (Y and La) in the system was investigated on the local structure and associated photoluminescence properties by various characterization techniques. Both trivalent ion substitutions lead to the same kind of variation during phase transformation from fluorite to the respective parent oxide structure (x ≥ 0.6). On the other hand, the substitutions have a distinct effect on local structure, absorption, luminescence and lifetimes. The smaller Y ion substitution enables the ordering of oxygen vacancies in a lattice, inhibiting the defect formation of Ce oxidation states. In contrast, the larger La ion substitution liberates oxygen vacancies, allowing defect formation. Consequently, the concentration of Ce is dependent on the ionic radius of the metal ions and it has a bearing on the band gap and luminescence properties of the system. CeYO:0.1Eu phosphor exhibited maximum red emission intensity at 612 nm, which is 8 times higher than that of CeO:0.1Eu and better than that of commercial Philips red phosphor, whereas La substitution yielded poor emission intensities with higher concentrations. The co-substitution of contrasting rare earth metals with Eu allow the understanding of local structure and a smaller ion like Y greatly functionalizes CeO:Eu phosphor.

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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.