Long-afterglow phosphor SrAl2O4: 0.01Eu(2+), 0.01Dy(3+) (SAO) requires a high sintering temperature of 1400 degrees C even when boric acid is added as flux via a solid-state reaction. The aluminum source NaAlO2 behaved as a good mineralizer in the designed hydrothermal process to achieve a large surface-to-thickness ratio of SAO. The flower-like shape of hydrothermally prepared hSAO without B2O3 after annealing at 1100 degrees C/4 h transformed into a rod-like plate phosphor with nano-thickness. Such a small rod-like plate exhibited higher photoluminescence (PL) intensity than large-grained B2O3-added bSAO prepared via a solid-state reaction. The annealed hSAOs inherited the morphology of the as-hydrothermally prepared aluminates. A nano-thick sheet of annealed aSAO containing B2O3 further enhanced the PL significantly and indicated a blue shift independent of the grain size. Furthermore, the nano-thick sheet of phosphors exhibited the same afterglow as the conventional tens-of-micrometers-sized phosphors. Fourier-transform infrared spectroscopy and X-ray diffraction results showed that the B-O-4 bond may substitute Al-O-4 in the structure and the B-O-3 bond is in a flux outside the annealed aSAO and bSAO grains. The molten flux formed a thin layer on the surface of the SAO particles to be a core-shell of the SAO-B2O3 structure, behaving as a diffusion-assistant medium and environmental protection layer against acid and humidity. (c) 2018 Elsevier B.V. All rights reserved.
