Synthesis and optical properties of turquoise- and green-colored brownmillerite-type Ba2In2−x−y Mn x Al y O5+x codoped with manganese and aluminum

Brownmillerite-type oxides Ba 2 In 2− x − y Mn x Al y O 5+ x (0 ≤ x ≤ 0.6, 0 ≤ y ≤ 0.5) were prepared at 1300°C through solid-state reaction. X-ray diffraction (XRD) analysis showed that the structure symmetry evolved from orthorhombic to cubic with increasing Mn and Al contents. When y was greater than 0.3, peaks associated with small amounts of BaAl 2 O 4 and Ba 2 InAlO 5 impurities were observed in the XRD patterns. When substituted with a small amount of Mn ( x ≤ 0.3), the Ba 2 In 2− x − y Mn x Al y O 5+ x samples exhibited an intense turquoise color. The color changed to green and dark-green with increasing Mn concentration. UV–vis absorbance spectra revealed that the color changed only slightly upon Al doping. The valence state of Mn ions in Ba 2 In 2− x − y Mn x Al y O 5+ x was confirmed to be +5 on the basis of X-ray photoelectron spectroscopic analysis. According to this analysis, the intense turquoise color of the Ba 2 In 2− x − y Mn x Al y O 5+ x samples is rooted in the existence of Mn 5+ ; thus, the introduction of Al does not affect the optical properties of the compounds.