Structure and luminescence of core-shell phosphor aluminate-boron oxide

Abstract Long-afterglow phosphor SrAl 2 O 4 : 0.01Eu 2+ , 0.01Dy 3+ (SAO) requires a high sintering temperature of 1400 °C even when boric acid is added as flux via a solid-state reaction. The aluminum source NaAlO 2 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 B 2 O 3 after annealing at 1100 °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 B 2 O 3 -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 B 2 O 3 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-B 2 O 3 structure, behaving as a diffusion-assistant medium and environmental protection layer against acid and humidity.