Synthesis and optical properties of Cr-doped Ba2In2O5 orange-brown oxides

Cr-doped Ba2In2-xCrxO5+y (0 ≤ x ≤ 0.5) orange-brown inorganic oxides have been successfully synthesized by solid-state reaction. X-ray diffraction (XRD) patterns show that their crystal structures transform from orthorhombic to cubic by increasing the Cr doping amount. Field emission scanning electron microscopy (FESEM) measurements show powder particles of irregular shape with average particle size of about 10 µm. The colors of the compounds are tuned from light yellow (x = 0) to orange (x = 0.1) and then to dark brown (x = 0.5). X-ray photoelectron spectroscopy and UV-Vis absorption spectroscopy demonstrate the oxidation state of Cr to be + 6 and the change in color to be due to the metal-ligand charge transfer of Cr6+-O2-.