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Synthesis by solution combustion of inorganic blue pigments MFe2(P2O7)2: Influence of the cation M (Zn2+, Co2+, Cu2+, and Mg2+) on their optical properties

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Abstract The aim of this work is to find the effect of the cation M (Zn2+, Co2+, Cu2+, and Mg2+) on the optical properties of MFe2(P2O7)2 synthesized by solution combustion. The crystal structure of the powders was determined by X-ray diffraction (XRD), Infrared spectroscopy (IR), and Raman spectroscopy. The presence of Fe2+ and Fe3+ ions in the pigments was studied using Mossbauer spectroscopy (MS), these spectra showed at 298 K three well-defined Mossbauer doublets belonging to octahedral S1 site and S3 site of Fe3+ and trigonal prismatic S2 site of Fe2+, confirming the formation of ZnFe2(P2O7)2, CoFe2(P2O7)2 and MgFe2(P2O7)2 structures, while in CuFe2(P2O7)2 there is no presence of trigonal prismatic S2 site of Fe2+ ion. Therefore, the mechanism of color on the ZnFe2(P2O7)2, CoFe2(P2O7)2, and MgFe2(P2O7)2 structures are due to intervalence charge transfer between Fe2+ and Fe3+ ions. In contrast, on the CuFe2(P2O7)2 structure is due to d-d electronic transitions of the Cu2+ ion, these evidences can also be observed in their UV–Vis diffuse reflectance spectra. Moreover, the inorganic blue pigment MgFe2(P2O7)2, which is free of cobalt, copper, and zinc could be used as a pigment in applications of low temperatures.