Characterization of structural orientation and optical properties of Al and Cr in rubies

We study the correlation between the structural orientation and the chromatic characteristics in rubies by combining X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and density functional theory (DFT) calculations. The chemical compositions were investigated by X-ray fluorescence (XRF). XRD result shows the preferred orientation of Al2O3 crystals as the (113), (110), and (223) plans. The local site and structural orientation of Cr impurities were investigated by the XAS technique, which prefers [141] and [411] polarizations. The optical absorption energy was estimated according to UV–visible spectroscopy. The results show the impurity state that relates to the optical absorption and emission energies. More importantly, the results show that the information on the locally determined structures and their effect on energy levels in rubies were obtained and discussed.