Icosahedral order has been suggested as the prevalent atomic motif of supercooled liquids and metallic glasses for more than half a century, because the icosahedron is highly close-packed but is difficult to grow, owing to structure frustration and the lack of translational periodicity. By means of angstrom-beam electron diffraction of single icosahedra, we report experimental observation of local icosahedral order in metallic glasses. All the detected icosahedra were found to be distorted with partially face-centered cubic symmetry, presenting compelling evidence on geometric frustration of local icosahedral order in metallic glasses.

We measured the fluorescence quantum yield (Φf) of several aromatic hydrocarbon crystals: p-terphenyl, trans-stilbene, anthracene, pyrene, and α-perylene. The Φf is reduced by chemical impurities, structural defects, and reabsorption of fluorescence. To minimize the effect of chemical impurities and structural defects, we evaluated the Φf of highly purified single crystals. We also measured the Φf of powder samples prepared by the mechanical milling of single crystals to assess the effect of reabsorption and structural defects induced by milling. We estimated the lower limit values of the Φf to be 0.80 for p-terphenyl, >0.65 for trans-stilbene, >0.64 for anthracene, 0.68 for pyrene, and 0.31 for α-perylene.