Enhanced pigmentary properties of rare earth germanates of the type La2CuGe2O8 through CuO6 octahedron distortion

- New Cu2+ based pigments La2Cu1-xLixGe2-xPxO8 were developed.
- The chromatic properties are enhanced by Li+ doping in the Cu2+ site.
- d-d transition of Cu2+ in the distorted octahedra causes the blue - green color.
- They impart good color characteristics on PMMA, concrete block and metal Plate.
- The synthesized pigments are environmentally friendly.

Copper based blue-green inorganic pigments, La2Cu1-xLixGe2-xPxO8 (x = 0, 0.1, 0.2 & 0.3) were synthesized by a conventional solid state method. Absorption spectra measurement reveals that the origin of the color is due to the crystal field splitting of Cu2+ ions in the distorted octahedral field. Optical properties of the synthesized samples are enhanced with the doping of monovalent (Li+) in the Cu2+ site. We suggest that the polarizability of the oxygen ion of Cu-O/Li-O bonds in the solid solutions tunes the crystal field strength around Cu2+ ion such that a intense blue-green color results for materials with small values of x. Among the samples the most vivid hue was obtained for La2Cu0.8Li0.2Ge1.8P0.2O8 with a CIE greenness value of (a* = −38.71). Studies on the coloring applications of the prepared pigments in poly(methyl methacrylate), concrete cement block and metal plate demonstrate their ability to transfer color and NIR reflectance.

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