Melilite-type blue chromophores based on Mn~(3+) in a trigonal-bipyramidal coordination induced by interstitial oxygen

摘要

A new, earth-abundant, environmentally benign, and stable inorganic blue chromophore series Sr2(Mg_(1-x)lvln_x)Ge2O_(7+δ) has been prepared and characterized by X-ray absorption spectroscopy, synchrotron X-ray diffraction, and ab initio total energy calculation. As the content of Mn in the compound was increased, the color changed from white (for x = 0.0) to sky blue, deep blue, and finally black body color (for x = 1.0). Sr2Mg2O7 has the melilite-type structure comprising Mg(2+)O4 and GeO4 tetrahedra. On the other hand, it was found that the Mn ion in Sr2(Mg_(1-x)lvln_x)Ge2O_(7+δ) is mainly trivalent and that the additional oxygen atom infiltrates into the lattice to compensate for the excess positive charge. The additional oxygen atom occupies an interstitial site, leading to the formation of Mn(3+)O5 trigonal bipyramid and Ge(4+)O5 square pyramid. As the driving force for the Mn(3+)05 formation, the tendency for improving the lattice coherency between BO4-BO4 and AO8 layers in the melilite A2BB'2O7 is suggested.